AAMC CBT9 and 9R OFFICIAL Q&A

[Vihsadas]

This is the official Q&A thread for AAMC CBT9 and 9R.

Please post ONLY questions pertaining to AAMC CBT9 and 9R.
Out of respect for people who may not have completed the other exams, do not post questions or material from any other AAMC exam.

Please see this thread for the rules of order before you post.

Good luck on your MCAT!

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[Marjan Islam]

Also, momentum isn't conserved in SHM because there is a change in direction. Momentum is a vector, mv where velocity has a + and a - depending on which direction you choose. Since the wave moves right, then stops and moves left, direction changes and momentum isn't conserved.

 

[loveoforganic]

Would you say a ball bouncing off of a rigid wall doesn't exhibit conservation of momentum?

 

[neil100]

For those that have taken the AAMC practice test #9, this is the question about water sloshing back and forth (seiches and "dry water"). Dry water here just means a model of water that doesn't take into account viscosity.

"Assume that a pan of “dry water” is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time?"
A) Energy conservation
B) Momentum conservation
C) Newton's 3rd law
D) Archimedes' principle

I was eyeballing A and B, and put B. The answer was A. The rationale given is:

"Although some friction (energy loss) will take place, energy will be very nearly conserved over each oscillation period. As a result, the amplitude of the seiches will decay very slowly as mechanical energy is turned into heat. The other options do not pertain to the sloshing oscillations. Thus, A is the best answer."

Can someone give me a more detailed analysis for why momentum conservation doesn't apply here? I accept that energy conservation is going on, but isn't momentum conservation also going on?

Thanks!

The concept of Energy conservation best applies here. They are testing the continuous conversion of energy between oscillations as the explanation nicely states. B is a little reach answer because we aren't talking about collisions with objects/particles.

To me in these types of questions you have to figure out what they are really after. AAMC is pretty straightforward with what they want. Here they wanted conversation of energy which is the first thing that came to my mind. Think about grandfather clock and how the pendulum swings back and forth despite some air resistance.

 

[vickpick]

For those that have taken the AAMC practice test #9, this is the question about water sloshing back and forth (seiches and "dry water"). Dry water here just means a model of water that doesn't take into account viscosity.

"Assume that a pan of “dry water” is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time?"
A) Energy conservation
B) Momentum conservation
C) Newton's 3rd law
D) Archimedes' principle

I was eyeballing A and B, and put B. The answer was A. The rationale given is:

"Although some friction (energy loss) will take place, energy will be very nearly conserved over each oscillation period. As a result, the amplitude of the seiches will decay very slowly as mechanical energy is turned into heat. The other options do not pertain to the sloshing oscillations. Thus, A is the best answer."

Can someone give me a more detailed analysis for why momentum conservation doesn't apply here? I accept that energy conservation is going on, but isn't momentum conservation also going on?

Thanks!

momentum isnt conserved because when the wave bounces off the side of the pan, the direction changes and velocity is vectoral..

 

[vickpick]

For those that have taken the AAMC practice test #9, this is the question about water sloshing back and forth (seiches and "dry water"). Dry water here just means a model of water that doesn't take into account viscosity.

"Assume that a pan of “dry water” is momentarily disturbed. Which of the following concepts best explains why the resulting sloshing oscillations persist for a fairly long time?"
A) Energy conservation
B) Momentum conservation
C) Newton's 3rd law
D) Archimedes' principle

I was eyeballing A and B, and put B. The answer was A. The rationale given is:

"Although some friction (energy loss) will take place, energy will be very nearly conserved over each oscillation period. As a result, the amplitude of the seiches will decay very slowly as mechanical energy is turned into heat. The other options do not pertain to the sloshing oscillations. Thus, A is the best answer."

Can someone give me a more detailed analysis for why momentum conservation doesn't apply here? I accept that energy conservation is going on, but isn't momentum conservation also going on?

Thanks!

momentum isnt conserved because when the wave bounces off the side of the pan, the direction changes and velocity is vectoral..

but i see marjan islam already pointed that out..

 

[Vihsadas]

Hey guys,
Please try and keep the AAMC exam questions that you have in the relevant thread that's been created for each specific AAMC practice test. The AAMC practice tests are a vital tool for your fellow studiers, so we wouldn't want anyone who hasn't take the exam yet to accidentally click on this thread and see the answer to a questions on it. See the "Rules of order" stickied thread at the top, thanks!
I'm merging this thread now.

 

[bigslick]

Hi, can someone provide a quick summary of Passage IV of the verbal reasoning section for CBT9? Not very long, just like what the point of it is. It's a philosophy passage, and like other philosophy passages, I can never understand anything the author is saying, leading me to miss 4 out of the 5 questions in this section (with the one I got correct by luck). My test is this Saturday, and my goal right now is pretty much just trying to understand at least one philosophy passage before I go in.

The passage starts out like.. "Nature is extraordinarily fertile and ingenious in devising means"

Thanks!

 

[chipaev]

This question confused me also. The concentrations of sodium in the dialysate are comparable to that in the blood, yes, but doesn't that just make the solutions isotonic with respect to sodium and not mean that the isotonicity of the dialysate solution is the same as blood when you consider all of the solute molecules present? I chose answer A through some complicated logic which I'm not sure made sense, but I don't understand answer C. If the dialysate solution were isotonic to the blood because of the Na+ concentration, then wouldn't there be no movement of fluid across the membrane--i.e. - wouldn't the dialysis machine fail to remove "excess fluid" as the passage indicates?

In general, when you say that a fluid is "isotonic" or "hypertonic" or "hypotonic", doesn't that refer to the entire solute composition rather than a single solute molecule as tonicity is a colligative property where the number of particles and not the identity matters??

Any response on these questions would be really appreciated...I take the test on Friday and want to make sure I don't head into it with the wrong understanding of these concepts. Thanks!!

This confused me as well and would like to hear someone's take on it. Basically, I don't understand how we are supposed to know that isotonicity is supposed to take place by a high Na concentration. The only thing I could come up with was that it was to balance out the Urea concentration but I knew that was wrong I just didn't know what was right. The kidney is certainly not isotonic in its filtering so I assumed that the dialysis machine would not be either.

 

[cathyrn]

could someone please explain why C can't be an answer to question 45? about diverging rays?

 

[cathyrn]

i am also confused by PS #26. Thinking about a pendulum..v is zero at the highest point and max at the equilibrum. PLease explain why the answer is B?

 

[lychee3]

I'm confused as to the difference between H in the equation (height of the liquid) and the amplitude of the wave.

If the atmospheric pressure induces a seiche at one end of the lake, wouldn't it change the value of H and hence the value of f??

 

[cwfergus]

could someone please explain why C can't be an answer to question 45? about diverging rays?

Draw out a diverging lens' rays. They will diverge past the lens, with the reflected rays converging back to the initial point.

Here, ill find one online..

http://www.antonine-education.co.uk/physics_a2/options/Module_6/Topic_2/ray_diag_7.gif

Reflected rays are converging, but the refracted (not sure if that's the right term to use on that one) ones are diverging

 

[Chowdder]

I'm confused as to the difference between H in the equation (height of the liquid) and the amplitude of the wave.

If the atmospheric pressure induces a seiche at one end of the lake, wouldn't it change the value of H and hence the value of f??

I think you've misunderstood the equation from the question. The H does not denote the H of the amplitude, the H denotes the height of the fluid (the depth of the lake in this case). So If a drop in atmospheric pressure occurs on one side of the lake then there will be a change in the amplitude (now much pressure is pushing down on the water), not the frequency (since the depth of the lake has not been change).

Another way to eliminate that answer choice is by looking at A and B. Frequency is inversely related to period. If you change frequency then you change period. Since both can not be correct, then both are automatically incorrect. While I'm at it, C is incorrect because speed of a wave is independent of amplitude. Instead it is determined by the medium the wave is travelling in (i.e. sound travels faster through water than air).

 

[Chowdder]

i am also confused by PS #26. Thinking about a pendulum..v is zero at the highest point and max at the equilibrum. PLease explain why the answer is B?

In this type of question, if you're unsure of the answer choices, then draw out the displacement of the liquid air interface at time 0 and at time III (position where interface III is at).

A doesn't make sense because it means all the liquid is rising up, which is not the case

C is incorrect because it means the edges of the liquid is rising, so you get a U shaped liquid air interface (not the case again)

D is just like C except the inverse where instead of a U you get an n shaped liquid air interface (not the case again).

B is correct because if you draw out II and III you can see that's the only diagram that can get you from II to III.

 

[starbaduk]

I think momentum is conserved as well, by way of pendulum bob bouncing off air molecules and air molecules acting on the bob. But that's not what's driving the pendulum.

 

[Bernoull]

Suppose a newly discovered fossil agnathan skull (with its enclosed fossilized brain) shows a fully vascular connection between the hypothalamus and the pituitary. This finding supports which of the following statements about the evolution of the vertebrate hypothalamic-pituitary axis?

A
) Ancient agnathans possess degenerate axes.
B
) Ancient agnathan axes are similar to existing bird axes.
C
) Existing agnathan axes are similar to ancient vertebrate axes.
D
) Mammals are more similar to existing agnathans than to ancient agnathans.
The question proposes that a newly discovered fossilized agnathan skull shows a fully vascular connection between the hypothalamus and pituitary, and then asks the examinee to indicate which statement is supported by this finding. According to the passage, all vertebrates except the existing agnathans have this vascular connection. A is incorrect because ancient agnathans possess the portal system as do higher vertebrates and therefore do not possess degenerate axes. B is correct because this evidence supports the idea that ancient agnathans are similar to existing birds (vertebrates) in having the vascular connection. C is incorrect because existing agnathans, which lack a functional hypothalamic-pituitary system, are not similar to the ancient agnathans (vertebrates), which are proposed to have the system. D is incorrect because mammals, by having the vascular connection, are more similar to ancient agnathans than to existing agnathans, which lack the vascular connection. Thus, B is the best answer.


My question is if choice A said Existing rather than Ancient, it will be correct right. My brain somehow saw the word Ancient and interpreted it as Existing!!

thanks

 

[Chowdder]

Can't remember the passage directly off the top of my head, but if I do recall they talked about agnathans having a degenerate portal vascular system. So if a fossil discovered shows a full portal vessel network, then it would suggest existing ones have a degenerate axes.

 

[Bernoull]

In the year 2010, a paleontologist provides convincing evidence that existing agnathans have been incorrectly classified and should belong to an earlier and previously undescribed vertebrate class. Fossils of this newly described class lack a pituitary portal system. This finding suggests that the new class of vertebrates (including agnathans):
A) represents a degenerative state.
B) represents an ancestral state.
C) represents a newly derived state.
D) is similar to other classes of living vertebrates.


The question asks the examinee to interpret new hypothetical evidence. The evidence indicates that agnathans have been incorrectly classified and should belong to a previously undescribed vertebrate class. Fossils of this new vertebrate class lack a pituitary portal system, as do existing agnathans. This evidence does not suggest that the new class represents a degenerative state because both the ancient and the existing members of the class lack the pituitary portal system; therefore, A is incorrect. The evidence does suggest that the new class represents an ancestral state because both the existing and the ancient members of the class lack the pituitary portal system; therefore, B is correct. C is incorrect because the paleontologist gives evidence, including fossil evidence, that this class represents a more ancient and not a newly derived state. D is incorrect because the new class lacks the portal system, unlike other classes of vertebrates. Thus, B is the best answer.

Question: Does answer choice B assume that agnathans will in the future develop a pituitary portal system, since the ancestral state requires the organism to develop the vascular connection later in the vertebrate lineage.

If this is the assumption, is it a reasonableone? Is there reason to believe that just because agnathans are vertebrates that will NECESSARILY evolve this feature? I chose D bcos well agnathans are vertebrates and so are similar to other vertebrates in many respects (obviously) although they are dissimilar wrt to this archaeological finding.

Thanks for any feedback..

 

[Bernoull]

Can't remember the passage directly off the top of my head, but if I do recall they talked about agnathans having a degenerate portal vascular system. So if a fossil discovered shows a full portal vessel network, then it would suggest existing ones have a degenerate axes.

Thanks, that's the correct reasoning. I gotta pay attention to key words i guess!!

 

[ahs4n]

If one mole of each additive shown in Table 1 undergoes complete combustion, which compound requires the least amount of oxygen?
A) MTBE
B) ETOH

The compound with the lowest carbon-to-oxygen ratio will require the least amount of oxygen for combustion. ETOH has only two carbon atoms and one oxygen atom. Thus, B is the best answer.






Is this solution applicable when you use other reactants on other compounds?

 

[ahs4n]

The actual oscillating surface in Figure 1 would not remain precisely flat; it would have a half-sine-wave shape. Use this fact to determine the wavespeed v of the fundamental mode of oscillation.
A) v = (2gH)1/2
B) v = (3gH)1/2
C) v = (3gH)1/2/π
D) v = 2(3gH)1/2/π
The wave speed v is given by the product of f and the wavelength λ. Because L is one-half of a wavelength (just like a standing wave in a tube of length L at its fundamental vibration), v will be

Thus, D is the best answer.




Sorry another question...what is a half sine way and how do you get the length of 2L

 

[Bernoull]

The actual oscillating surface in Figure 1 would not remain precisely flat; it would have a half-sine-wave shape. Use this fact to determine the wavespeed v of the fundamental mode of oscillation.
A) v = (2gH)1/2
B) v = (3gH)1/2
C) v = (3gH)1/2/π
D) v = 2(3gH)1/2/π
The wave speed v is given by the product of f and the wavelength λ. Because L is one-half of a wavelength (just like a standing wave in a tube of length L at its fundamental vibration), v will be

Thus, D is the best answer.




Sorry another question...what is a half sine way and how do you get the length of 2L

This is half sine wave ----> U

If u tie a rope at one end and shake the other, u make sine waves, a sine wave is from any point to another point where the pattern repeats (2pi radians) and half of that = half sine wave (pi radians). Think of sine/cosine fns from trig

Finding L comes from harmonics (although I didn't think of this during da exam, i did it differently n got lucky), the length of the tank is 1/2 the first harmonic wavelength. Formula is: L=n*lambda/2 (n= counting #s).

The key to the problem was recognizing "fundamental mode of oscillation" refers to fundamental freq n lambda...

 

[ahs4n]

Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?
A) Net fluid flow in the direction of interstitial spaces will increase.
B) Net fluid flow in the direction of interstitial spaces will decrease.
C) Capillary osmotic pressure will increase.
D) Capillary osmotic pressure will decrease.


After introducing the idea of fluid homeostasis, which is obtained by balancing hydrostatic and osmotic pressures, the question asks the examinee to predict the consequences of a blood clot on the venous side of a capillary bed. To answer this, it is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. A is therefore correct. B is incorrect because there will be an increase in net fluid flow into the interstitial spaces, not a decrease. C is not the best answer because the increase in osmotic pressure in the capillaries would be an indirect result of the fluid flow out of the capillaries. D is incorrect because the flow of fluid out of the capillaries would slightly increase, not decrease, the osmotic pressure. Thus, A is the best answer.




One more, sorry guys, I thought that since in the increase of proteins inside the capillary would cause an increasing osmotic pressure causing the the net flow inside the capillaries and thus, the net flow in the direction of the interstitial space would decrease.

 

[Bernoull]

Capillaries in the kidney and elsewhere in the body maintain fluid homeostasis by balancing hydrostatic and osmotic pressures. Which of the following is the initial effect of a blood clot forming on the venous side of a capillary bed?
A) Net fluid flow in the direction of interstitial spaces will increase.
B) Net fluid flow in the direction of interstitial spaces will decrease.
C) Capillary osmotic pressure will increase.
D) Capillary osmotic pressure will decrease.


After introducing the idea of fluid homeostasis, which is obtained by balancing hydrostatic and osmotic pressures, the question asks the examinee to predict the consequences of a blood clot on the venous side of a capillary bed. To answer this, it is necessary to know that blood flows from arteries to capillaries and then to veins. If flow is blocked at the venous side, blood would accumulate in the capillaries. Thus, hydrostatic pressure would build up in the capillaries, causing a net increase in fluid flow into the interstitial spaces. A is therefore correct. B is incorrect because there will be an increase in net fluid flow into the interstitial spaces, not a decrease. C is not the best answer because the increase in osmotic pressure in the capillaries would be an indirect result of the fluid flow out of the capillaries. D is incorrect because the flow of fluid out of the capillaries would slightly increase, not decrease, the osmotic pressure. Thus, A is the best answer.




One more, sorry guys, I thought that since in the increase of proteins inside the capillary would cause an increasing osmotic pressure causing the the net flow inside the capillaries and thus, the net flow in the direction of the interstitial space would decrease.

I reasoned exactly as you and missed the question. I think the problem is one of relativity, yes increased solutes (proteins, platelets etc...) in the capillary increase pi, but also hydrostatic pressure builds in a blocked pipe, so it's a battle b/t the two, which once increases to a greater magnitude dictates net fluid flow, and now i know hydrostatic increases more than pi..

 

[Bernoull]

In the year 2010, a paleontologist provides convincing evidence that existing agnathans have been incorrectly classified and should belong to an earlier and previously undescribed vertebrate class. Fossils of this newly described class lack a pituitary portal system. This finding suggests that the new class of vertebrates (including agnathans):
A) represents a degenerative state.
B) represents an ancestral state.
C) represents a newly derived state.
D) is similar to other classes of living vertebrates.


The question asks the examinee to interpret new hypothetical evidence. The evidence indicates that agnathans have been incorrectly classified and should belong to a previously undescribed vertebrate class. Fossils of this new vertebrate class lack a pituitary portal system, as do existing agnathans. This evidence does not suggest that the new class represents a degenerative state because both the ancient and the existing members of the class lack the pituitary portal system; therefore, A is incorrect. The evidence does suggest that the new class represents an ancestral state because both the existing and the ancient members of the class lack the pituitary portal system; therefore, B is correct. C is incorrect because the paleontologist gives evidence, including fossil evidence, that this class represents a more ancient and not a newly derived state. D is incorrect because the new class lacks the portal system, unlike other classes of vertebrates. Thus, B is the best answer.

Question: Does answer choice B assume that agnathans will in the future develop a pituitary portal system, since the ancestral state requires the organism to develop the vascular connection later in the vertebrate lineage.

If this is the assumption, is it a reasonableone? Is there reason to believe that just because agnathans are vertebrates that will NECESSARILY evolve this feature? I chose D bcos well agnathans are vertebrates and so are similar to other vertebrates in many respects (obviously) although they are dissimilar wrt to this archaeological finding.

Thanks for any feedback..

bump.. please respond ... someone... anyone

 

[ahs4n]

Thanks for anwering the question about blood clots...that makes sense to look at the whole underlying picture in perspective that the clot would actually block the venule side causing for an increasing hydrostatic pressure.

And for the agnathan question. I chose B on the reasoning that the hypothesis 1 assumes that vertebrates evolved from agnathan.

Because this finding gives support that agnathans never had the pituatory portal system in the first place, it gives support to hypothesis 1 because vertebrates evolved from the agnathans and developed the portal system later on in the lineage.

 

[Zona Pellucida]

BS 112:

I understand how Bicarbonate regulates Hydrogen ions... but doesn't it also maintain physiological levels of chloride by means of the "Chloride Shift"?

 

[G1SG2]

BS 112:

I understand how Bicarbonate regulates Hydrogen ions... but doesn't it also maintain physiological levels of chloride by means of the "Chloride Shift"?

I don't think it's bicarbonate that actually maintains the level of chloride. Here's something from wikipedia:

When carbon dioxide levels fall as the blood passes through the lungs, bicarbonate levels fall in the serum and bicarbonate moves out of the red blood cells. To balance the charges when bicarbonate exits the cell, a chloride anion from the plasma enters the red blood cell when the bicarbonate anion leaves. Reverse changes occur in the lungs when carbon dioxide is eliminated from the blood. Here, the exchange of bicarbonate for chloride in red blood cells flushes the bicarbonate from the blood and increases the rate of gas exchange.

So I think it has more to do with CO2 levels rather than bicarbonate in terms of maintaining the balance of charges.

 

[brushbordermb]

If the magnitude of a positive charge is tripled, what is the ratio of the original value of the electric field at a point to the new value of the electric field at the same point?
A- 1:2
B- 1:3
C- 1:6
D- 1:9

Now, I got the right answer. However, I get two contradicting answers depending on whether I use F=qE or whether I use E=Kq/r. Though only one answer makes sense, I can't understand why the same answer cannot be attained by using F=qE. Can someone reconcile this for me?

 

[EgyptianDoc]

Nevermind.

 

[waffle23]

For 131 on the Bio section, I really don't like the answer they give you. I put decreasing at first but then changed it. If you don't have it in front of you, it is basically a competitive inhibition question. Binding of A to a receptor causes a product to be made and B simply competitively inhibits. It asks what would happen if you increase B, to the concentration of the product. At first glance decrease seems obvious, but isn't it really the rate of the reaction, thus the rate of concentration change decreasing? Why would the actual concentration decrease? Suppose you completely saturate it with B, then the reaction stops but you still have the concentration of product - it's not like it went anywhere! If anything I think the rate will just simply keep on decreasing and therefore the concentration will actually increase, just at a slower rate. Any insight on this??

 

[thebillsfan]

PS #2




Why can't we set the kinetic energy= qXEXd? I thought the force would increase by a factor of 4 when the v is doubled.

is this because the kinetic energy of the electron is NOT the same potential energy that it has in the electric field?

 

[jikuty]

I guess I should post the question, that would probably help.

144. If chromosomal duplication before tetrad formation occurred twice during spermatogenesis, while the other steps of meiosis proceeded normally, which of the following would result from a single spermatocyte?

The Answer is B. Four Diploid Sperm. I put C. Four Haploid Sperm.

And I still can't make sense of how two rounds of duplication prior to the start of meiosis could lead to Four Diploid Sperm. The explanation AAMC gives is:"Because replication occurred twice instead of once prior to tetrad formation, each sperm would have twice the normal amount of DNA. As a result, four diploid sperm would be produced instead of four haploid sperm."

But I see a difference between having twice the normal amount of DNA to start and having twice the number of chromosomes.

And ignore my question about 113., I figured that one out with a little research. Good luck to everyone taking the test this weekend!

I have the same question. I was wondering if anyone could help me out here. It seems to me like you'll end up having 23 chromosomes in each sperm cell at the end, with each chromosome being composed of two sister chromatids - therefore making the result 4x haploid sperm cells.

 

[the prodogy]

On AAMC 9, there's a question on standard emf for a galvanic cell. (PS #30)
My only problem here is that, I thought that you have to multiply 2.71 since two sodium ions were used. Or do you not multiply it and just keep it the same. If anyone can get back to me on that, that would be much appreciated. Thanks!

 

[labellefille]

with EMF- you never multiply by number of moles, it is irrelevant.

so for this question Cl is being reduced (it has a positive reduction potential) and NA is being oxidized (a negative reduction potential, which is a positive oxidation potential)

so EMF= reduction potential of reduced species + oxidization potential of oxidized species
=(+1.36) + (+2.71)
= +4.07

 

[Vihsadas]

Hello,
Please remember to post questions about the AAMC practice exams only in the threads created for that purpose. Also, study questions in general should be posted in the Study Q&A forum.

We try to keep all of the official exam questions out of regular sight, so that people who have not taken the exams yet won't accidentally click on a thread and see a spoiler question. Thanks. For more info see this thread:
http://forums.studentdoctor.net/showthread.php?t=516243

I'll merge your thread with the offiicial AAMC 9 practice test thread now.

 

[hqt331]

has no one found a satisfactory answer to jikuty's question? i have the same question.

 

[kabtq9s]

This is not making sense... if the blood will build up in the capillaries wouldn't interstital fluids attempt to diffuse into the capillaries to dilute the blood ?

 

[ezsanche]

This is not making sense... if the blood will build up in the capillaries wouldn't interstital fluids attempt to diffuse into the capillaries to dilute the blood ?

Read Option C very closely. It said that OSMOTIC PRESSURE will build up. Osmotic pressure increases as the the concentration of proteins, ion, electrolytes, and other stuff in plasma increases.

If you block the venous end of the capillary then the fluid will increase in the capillary. The fluid needs to go somewhere so it will go in the interstital space. HYDrostatic pressure!

 

[Kanye West]

This is probably a really easy one:

#146

Why would uracil be incorporated into ribosomes? I know translation of mRNA occurs w/ ribosomes etc, so if that were see this uracil in ribosomes, it would first have to be incorporated into mRNA in the nucleus right? Did we have to just assume this happened?

I thought since it was just an extra thing floating around a lysosome would just digest it and get rid of it. How do we know this doesn't happen?

 

[hqt331]

This is probably a really easy one:

#146

Why would uracil be incorporated into ribosomes? I know translation of mRNA occurs w/ ribosomes etc, so if that were see this uracil in ribosomes, it would first have to be incorporated into mRNA in the nucleus right? Did we have to just assume this happened?

I thought since it was just an extra thing floating around a lysosome would just digest it and get rid of it. How do we know this doesn't happen?

Ribosomes are made of RNA. Therefore, uracil, would be incorporated into ribosomes.

 

[kabtq9s]

Guys, I did not really understand how they came up with this formula for this answer... I was lucky to guess correctly

can somebody plz explain it to me (I prefer an explanation based on TPR books, but anything will do)

How come there is a (cos)? is this an inclined plane problem or a friction problem ? friction equations dont have any cos or sin in them as far as I see in my TPR book

plz hurry .. my exam is tommorow

 

[burningheat]

Momentum (p) = m*v. Photons don't have mass, therefore they don't have momentum. Thats why A can't work.

This is completely false. E-M waves (light, photons whatever) transport linear momentum as well as energy, which will later lead to pressure. A perfectly reflecting surface would experience twice the momentum as black body object, due to the momentum of the wave reflecting.

the formula is defined through the use of pointing vector and is actually the cause of radiation pressure. A large , reflecting "sail" in space would actually travel and be pushed by the light from the sun if attached to some craft.

the derivation results in P (pressure) = S(pointing vector)/ c(speed of light)

for complete absorption, double the right side for reflecting surface.

I have no clue how this relates to the problem and I guess the answer is just C because thats what happens? but em waves do carry momentum!

 

[burningheat]

huh? force its diagonal so there is x component and y component... due to the angle they give, cos i s the horizonal component and because no acceleration all horizonal components must equal, so frictional force must equal horizonatal force due to the pulling...

Guys, I did not really understand how they came up with this formula for this answer... I was lucky to guess correctly

can somebody plz explain it to me (I prefer an explanation based on TPR books, but anything will do)

How come there is a (cos)? is this an inclined plane problem or a friction problem ? friction equations dont have any cos or sin in them as far as I see in my TPR book

plz hurry .. my exam is tommorow

 

[violence]

PS #42:

Solution: At 1 atm and 0ºC, the volume of 1.5 mol CO2 is (22.4 L / 1 mol) × 1.5 mol = 33.6 L

I don't understand how to get 22.4L/mol for the vol of CO2. Why do I multiply but 1.5 mol a second time?

 

[dragon529]

PS #42:

Solution: At 1 atm and 0ºC, the volume of 1.5 mol CO2 is (22.4 L / 1 mol) × 1.5 mol = 33.6 L

I don't understand how to get 22.4L/mol for the vol of CO2. Why do I multiply but 1.5 mol a second time?

At STP, the molar volume of an ideal gas is defined as 22.4 L

 

[thegreatergood]

For 131 on the Bio section, I really don't like the answer they give you. I put decreasing at first but then changed it. If you don't have it in front of you, it is basically a competitive inhibition question. Binding of A to a receptor causes a product to be made and B simply competitively inhibits. It asks what would happen if you increase B, to the concentration of the product. At first glance decrease seems obvious, but isn't it really the rate of the reaction, thus the rate of concentration change decreasing? Why would the actual concentration decrease? Suppose you completely saturate it with B, then the reaction stops but you still have the concentration of product - it's not like it went anywhere! If anything I think the rate will just simply keep on decreasing and therefore the concentration will actually increase, just at a slower rate. Any insight on this??

I agree, the rate of production of osteoblatin decreases, but why would the CONCENTRATION change? Kaplan says decreases is the correct answer, but it explains it by saying production decreases (doesn't really talk about concentration). Anyone understand this?

 

[ronaldo23]

question 26 on the PS...about the oscillating water ... why is the velocity the least at the middle? I thought of this question using principles of pendulum motion, where the PE is max at the highest poitn and KE is min, while the PE is 0 at the bottom and max at 0 displacement. Why does this logic not apply here?

 

[wanderer]

question 26 on the PS...about the oscillating water ... why is the velocity the least at the middle? I thought of this question using principles of pendulum motion, where the PE is max at the highest poitn and KE is min, while the PE is 0 at the bottom and max at 0 displacement. Why does this logic not apply here?

Huh? It would be easier if I could see the entire question, but I'd imagine the question deals with there being a node right in the middle. At the node there is no displacement and the velocity is always zero. Hope this helps.

 

[Toolmatica]

Solution

Mark Visible light travels more slowly through an optically dense medium than through a vacuum. A possible explanation for this could be that the light:
answer: is absorbed and re-emitted by the atomic structure of the optically dense medium

According to kaplan, the answer was basically emission of photons by relaxing electrons. In that case some energy is lost to nonconservative forces and the wavelength of light will increase.

Question 1: wouldn't a longer wavelength and unchanged frequency mean that the speed of light increases?

Question 2: if light passes from air to water back to air, isn't the initial velocity in air going to be equal to the final velocity in air? If the answer is correct as they state it, it wouldn't be because some of the lights energy would be lost to nonconservative forces. Thanks.