aamc cbt11 thread

[sekistudent]

Can we start an official aamc cbt11 thread. I took this test a few days ago and have some questions. Can I just start this thread? Or, is that sort of behavior for the more senior members.

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[mcloaf]

Well, I'm not normally one to resurrect zombie threads, but as this seems to be the only one on CBT11 here goes.

Was I the only person bothered by the answer to Q79 in passage 5 of the VR?

Initially I had selected the correct answer about the acromion process, but I marked it and so was giving it another look before I ended the section. Upon closer reading the 5th paragraph begins with its assertion about "distinctive anatomical traits of turtles" and then goes on to give examples. The subsequent paragraph then begins with "another example[...]." I took this to mean (and I believe I'm correct) that the subsequently mentioned acromion process is an example of those samesaid distinctive anatomical traits they've been examining. What else could this be an example of that the author is discussing?

With this thought process I chose B, having already eliminated C and D as clearly wrong. B could be possibly answered by the passage, but it seemed to me to be more of a stretch than A considering the above. And yet lo and behold, A was correct because "there is no information about whether this particular feature occurs in other animal species."

Maybe I'm way off base here...

 

[snowpup]

Can someone explain why choice B is incorrect for question 124 on the Biological Science section? I narrowed down to choice B and C, I chose C while answering the question. I understand choice C make sense, but does anyone know why choice B is wrong? Thank you in advance for your explanation!!!

 

[s3dition]

I picked D, "opposition, because the author would believe that such a policy should not be based on a quota system" because of the passage sentence:

"First, academia has to overcome its prejudice against the local and the provincial, so that its hiring committees do not include non-native status as an implicit qualification for employment."​

Does that sentence not oppose the use of quotas?

 

[MedChad]

Two questions for you guys.

1.) Was the biology passage 6 on this exam extremely difficult for you to interrupt efficiently or is this just me?

2.) is number 145 in the bio section that states:

A compound shown in which of the following structures contains a methyl group with an axial orientation in its predominant conformation?
It shows three options

https://www.e-mcat.com/ITDVersions/...gramid=19&language=ENU&urid=PT11_2/O11484.gif

a. 1 only
b. 2 only
c.1 and 3
d.2 and 3

Thanks in advance for your help you guys!!

 

[el indio]

first let me say that overall this test seemed more difficult/had more critical thinking than the previous CBTs. After reviewing it I found out I made some dumb mistakes and that this test really isn't too bad, but under timed conditions and emotions it is easy to fall into traps

1) Yes, I felt passage 6 to be confusing...when you are reading fast, it becomes tough keep all the abbreviations in order and figure out what is happening. The chart also takes some time to figure out. I was already pressed for time when I got to this passage, so rushing through it made it worse. Also, microbio is my weakest topic and i have no background knowledge for it(physics and biochem undergrad)...maybe some people with more bio background made sense of it quicker

I ended up getting 3 out of 6 questions wrong on this passage, although 1 of those was #138 which doesn't require the passage

Reviewing the next day, I found it much easier to comprehend, but still needing effort. I understand all my mistakes including 138 which was due to not reading carefully (i.e. rushing due to lack of time)


2) There was a similar problem to this one on another AAMC test, which is the only reason why i was able to figure it out. The answer reasoning given by AAMC is actually decent (normally they suck). I just follow a simple set of rules to solve these after encountering it the first time:

1) find your substituent that predominates in the equatorial position and label that carbon 1
2) at positions 2, 4, and 6, any substituent that is trans to substituent 1 is equatorial; any that are cis will be axial
3) for positions 3 and 5, the opposite hold true: anything cis to substituent 1 is equatorial, and anything trans will be axial

in my own shorthand summary: even-cis and odd-trans = axial, even-trans and odd-cis are equatorial

for Compound I, the methyl is cis at 2----->axial
for Compound II, the methyl is cis at 3----->equatorial
for Compound III, the methyl is trans at 4-->equatorial

 

[alexrgross]

I picked D, "opposition, because the author would believe that such a policy should not be based on a quota system" because of the passage sentence:

"First, academia has to overcome its prejudice against the local and the provincial, so that its hiring committees do not include non-native status as an implicit qualification for employment."​

Does that sentence not oppose the use of quotas?

Maybe or maybe not, though the obvious theme of the passage is "traveling academics" are bad because they lack a sense of place. Even though authors implies he opposes quotas, he most likely would be happy that at least SOME of the factory will have a sense of place.

 

[MikeLin007]

Can someone explain PS #6 to me? I thought when temperature goes up, resistivity goes up. Wouldn't proton conductivity decrease with increasing temperatures?

 

[alexrgross]

Can someone explain PS #6 to me? I thought when temperature goes up, resistivity goes up. Wouldn't proton conductivity decrease with increasing temperatures?

Ceramic is a semi-conductor, and for this material resistivity decreases with increased temperatures. Do not think about that though, the passage states that the ceramic has high proton conductivity at high temperatures - its true!

The reason SCY is used is to pull protons from the hot anode, favorable conditions for hydrogen oxidation, to the cold cathode, where nitrogen is reduced.

This question is testing knowledge about equilbrium; the last sentence in the passage says that in the Haber process, like the SCY-catalyzed synthesis, only cold temperature limits the reverse of reaction 3. I only remember this because the Haber Process was very cool when I was in Gen Chem.
http://www.revisescience.co.uk/2010/images/haber2.gif

Basically, the only way for NH3 to be a product is at high temperatures, only it decomposes rapidly. So the NH3 has to be cooled fast to be collected, this SCY process sounds like a good way - it moving hot protons onto cold nitrogen, using electrolysis to deliver the energy instead of high pressure.

 

[slz1900]

On 135, how does it make sense that the proteases digest EGP? I get that's what proteases do, but the passage makes it sound like the proteases activate it so that the virus can infect a cell, so I chose the answer that says they dimerize EGP. Can someone explain?

 

[451617]

this is a free base question

was the answer derived somehow from the question stem or is this a common knowledge thing?

because it seemed like a random fact to me!

thanks for the help!

(don't know how to upload the pic directly, so i attached the image below)

 

[451617]

this is based on a passage that also includes a table

can someone describe their thought process in getting the answer?

i can list all the components necessary for melanosomes, but there is nothing in the written portion about what are/are not necessary for lytic granules. is it derived from the table?

(question stem is attached below as an image)


thanks again!

 

[Jay2910]

Hello everyone,

Here are some questions that I had on AAMC #11.

Item 136:
Question asks:
THE precursor of EGP, is translated from a transcript that has had one nontemplated nucleotide added to the open reading frame. This change, does not create or eliminate a stop codon. Compared with protein sGP, which is produced from the unedited transcript, EGP most likely has the same primary:

A) amino terminal sequence as sGP, but a different primary carboxyterminal sequence.
B) Carboxy terminal sequence as sGP but different primary amino terminal sequence
C) Sequence as sGP except that EGP has one additional amino acid
D) sequence as sGP except that EGP has one less amino acid.

I picked c, but I do not see how that is wrong and why the answer would be A. How could you add a nucleotide to the frame and not get a shift? I thought that it could be something like a silent point mutation. Any insight on this?

Item #122:
This question asks about cP-450 and isoenzymes . . . .aren't isoenzymes sometimes the product of alternate RNA splicing? Why isn't the answer B for this one? I thought that because RNA is spliced differently the amino acid sequence is different.
What does "amino acids that translate DNA" mean anyway? Cause translation means from RNA into Amino acid .. .. . does it perhaps mean, the amino acid sequence that is a product of the DNA sequence?

Item #114:
Melanosomes most likely move along microtubules that most likely radiate from the:
A) Centrosome
B) Kinetochores
C) Golgi
D) Microfilaments under plasma membrane

Why is the answer A? Aren't centrioles only coming into play during the cell division? So how can we have microtubules that radiate out of it during normal cell production?

Help would be awesome! I have been looking at these for a long time!

 

[Jay2910]

Here's another question that I have that needs clarification:
Question #21 on AAMC #11 asks:

Which one of the following properties of a wave is independent of all others?
A) Wavelength
B) Frequency
C) Velocity
D) Amplitude

I picked C but the answer is D.
The exact same question was asked in this website and C was the answer according to them.
So . . .. how do we solve this contradiction?

Here's the website:
http://www.physicsclassroom.com/reviews/waves/wavesans2.cfm#18

 

[Jay2910]

Sos!

 

[leonphelpss11]

Sos!

This may be late but...

The formula is c=(frequency)(wavelength). C=speed of light/velocity. Therefore, velocity=(frequency)(wavelength). Velocity, frequency, and wavelength are related. The only other answer choice that isn't is Amplitude.


I also have a question if anyone can help me out. On PS #38, the question about the hypothetical situation where X=Al, Xn=Al3+, Y=Cu, Ym=Cu2+, is there another way other than looking at the table to determine which ions get reduced/oxidized?

 

[DocMC]

Why can't MgSO4 be re-formed after mixture of the 2 solutions? And thus, the solubility of MgSO4 should be relevant, no??? I picked D) but it is B). Please explain!!! Thank you

 

[kanakari]

PS #11
Why is dG negative? It says that the reaction decomposes when heated. Would this not mean it doesn't decompose at room temperature?

also

BS#148
Alveolar walls are only composed of a single cell layer as opposed to single cell with underlying connective tissue. From anatomy class I know alveolar walls also have a basement membrane on them separating them from the blood vessels. Is that answer wrong because the connective tissue is 'overlying'?

 

[DocMC]

PS #11
Why is dG negative? It says that the reaction decomposes when heated. Would this not mean it doesn't decompose at room temperature?

also

BS#148
Alveolar walls are only composed of a single cell layer as opposed to single cell with underlying connective tissue. From anatomy class I know alveolar walls also have a basement membrane on them separating them from the blood vessels. Is that answer wrong because the connective tissue is 'overlying'?

Remember that reactions can be spontaneous and occur very slowly. It decomposes when heated because you are supplying it the activation energy for it to occur. This does not mean dG is positive. Every reaction needs energy to proceed, and not every spontaneous reaction occurs at a significant rate, some are extremely slow.

For your second Q. I picked the same as you. Still not really sure why it's wrong...

 

[Gauss44]

Map of passage #3 VR

Would you please share your map of passage #3 in VR about photography? I'm having difficulty seeing the structure and author's train of thought. Thank you.

 

[Gauss44]

#69
Please explain VR question #69. (I didn't think the author wanted to "discourage" photography. I thought he wanted to "limit" it. Having trouble understanding author's logic.)

Unrelated weird thing: I just missed the 69th post on here.

#54
Please explain #54 VR also if you can.

Thx.

 

[Gauss44]

Anyone?

 

[RC4L]

@Gauss44

69) The question is basically asking in what scenario would the author believe that photographs are distorting reality. The first answer choice is false because architectural models have a distinct and productive purpose and are not necessarily open to the public. The third option is incorrect because the author states in the passage that cameras can be **useful** in identifying criminals. The fourth answer choice is false and irrelevant because the passage does not discuss government and art directly. The second choice is correct because magazine articles are the only choice where photographs might subjectify or distort reality for the public in some way. For instance, the advertisement could be for lets say a depression medication with a picture depicting a happy couple on a date yet immediately below is a huge list of terrible side effects in fine print.

 

[RC4L]

54) The author is supporting the idea that Randi has been trying to teach the public *skills in critical thinking.* The scenarios presented in the passage are only examples of ways in which Randi tries to teach critical thinking. Answer choices II and III are assumptions based on Randi's experiments while choice I supports the point which the author is trying to drive across with the example of Randi.

 

[Synapsis]

Q100 in BS. This seems like it should've been easier, but I guess I overthought it. I picked C, because since LH controls estrogen secretion, and the table shows that when you have a the NPY alone you get less LH (albeit only a little), then I figured you'd get less estrogen. Now I know the reason it's A is because "there's no change", but my question is how exactly do I distinguish this? Yes, obviously the values are close, but the values with NPY alone are still lower than the control even though they're close. I figured since it wasn't like +/- 0.01 then it had it least some effect. This felt like one of those verbal questions where seemingly equally strong arguments for both choices could be given.

Can someone give some insight beyond just saying that the values are close so it had no effect?

 

[onedirection]

PS #21
Which of the following properties of a wave is independent of all others?

The answer was amplitude

but isn't frequency supposed to be an independent property of a wave?


#46
Which of the following best explains what happens at the molecular level to the supporting pillars as the water level in the storage tank rises?

I wasn't sure can someone explain why it's C?


Verbal
#74
Which subject would be most useful for an economics professor to know

#87
The authors imply that the portuguese ambassador applauded the french national assembly because of genuine sympathy for their ideals. Alternatively, the abassador's action could be explained as indicating that?

I guess A makes sense but I'm not sure where they are getting it from, also what about choice C?




BS
#108, 110


Ebola passage
131, 135, 136

 

[VitaminVater]

PS #21
Which of the following properties of a wave is independent of all others?

The answer was amplitude

but isn't frequency supposed to be an independent property of a wave?


#46
Which of the following best explains what happens at the molecular level to the supporting pillars as the water level in the storage tank rises?

I wasn't sure can someone explain why it's C?


Verbal
#74
Which subject would be most useful for an economics professor to know

#87
The authors imply that the portuguese ambassador applauded the french national assembly because of genuine sympathy for their ideals. Alternatively, the abassador's action could be explained as indicating that?

I guess A makes sense but I'm not sure where they are getting it from, also what about choice C?




BS
#110


Ebola passage
131, 135, 136

#21
Independent means if you change any of the other three, the correct one will stay the same. Amplitude never changes no matter what while frequency can change if you change the speed and keep wavelength constant, etc.. It's not specific like light or sound it's just asking about any wave.(Edit: amplitude can change with constructive/destructive interference)

#46 this one was confusing too, but just know if you compress something it gets hot, not cold(and so we can eliminate B). C fits the description best, when you compress something you bring its individual molecules closer together.

I'll get back to you on BS and VR when I get to them.

 

[onedirection]

Q100 in BS. This seems like it should've been easier, but I guess I overthought it. I picked C, because since LH controls estrogen secretion, and the table shows that when you have a the NPY alone you get less LH (albeit only a little), then I figured you'd get less estrogen. Now I know the reason it's A is because "there's no change", but my question is how exactly do I distinguish this? Yes, obviously the values are close, but the values with NPY alone are still lower than the control even though they're close. I figured since it wasn't like +/- 0.01 then it had it least some effect. This felt like one of those verbal questions where seemingly equally strong arguments for both choices could be given.

Can someone give some insight beyond just saying that the values are close so it had no effect?

There was no significant change also the passage says NPY only enhances the response to GnRH, it is not a releasing factor

 

[VitaminVater]

For #106 in BS
Are we seriously supposed to know which peptidases are made/located in which GI compartment?

 

[onedirection]

For #106 in BS
Are we seriously supposed to know which peptidases are made/located in which GI compartment?

I think you were talking about that question where the answer was trypsin

Trypsin is produced by the pancreas

The stomach enzyme is pepsin not trypsin

Also the other choices were what the stomach does

 

[VitaminVater]

I think you were talking about that question where the answer was trypsin

Trypsin is produced by the pancreas

The stomach enzyme is pepsin not trypsin

Also the other choices were what the stomach does

I'm pretty sure there are multiple stomach peptidases, which is why I assumed B was correct. I was trying so hard to decide between A and D when I just knew it definitely did both ughhh

 

[onedirection]

yeah stomach is involved with innate immunity

HCl creates the environment to convert pepsinogen to activated pepsin

and the proteins get denatured by the low pH for the attack

 

[gettheleadout]

124's explanation says "Acetyl coenzyme A is the end product of glycolysis..."

wat

Acetyl CoA is a product of pyruvate decarboxylation in the mitochondria, pyruvate is the end-product of glycolysis.

 

[gettheleadout]

Can anyone explain the reasoning on 136? I got the question correct, but now I realize my reasoning was fallacious and I don't understand that of the explanation.

The stem says a nucleotide was added to the ORF. Okay, fine. The explanation says we should expect a different amino acid at the C-terminus of the translated polypeptide. Why? We're not told where the nucleotide was added into the ORF (it could have been inserted anywhere, not necessarily added to the end), and even if it were added to the end, we wouldn't necessarily get a changed amino acid at the end of the polypeptide.

Furthermore how is it even possible to add in a single nucleotide and not create or eliminate a stop codon?

If the sGP mRNA sequence is this:

AUG|GCU|AUA|CUA|UGA

And we add a single nuc. in the ORF (before the stop codon), we get:

AUG|GCU|AUA|CUA|UUG|A

Which eliminates our stop codon because it shifts the reading frame.

I'm confused.

 

[onedirection]

Can anyone explain the reasoning on 136? I got the question correct, but now I realize my reasoning was fallacious and I don't understand that of the explanation.

The stem says a nucleotide was added to the ORF. Okay, fine. The explanation says we should expect a different amino acid at the C-terminus of the translated polypeptide. Why? We're not told where the nucleotide was added into the ORF (it could have been inserted anywhere, not necessarily added to the end), and even if it were added to the end, we wouldn't necessarily get a changed amino acid at the end of the polypeptide.

Furthermore how is it even possible to add in a single nucleotide and not create or eliminate a stop codon?

If the sGP mRNA sequence is this:

AUG|GCU|AUA|CUA|UGA

And we add a single nuc. in the ORF (before the stop codon), we get:

AUG|GCU|AUA|CUA|UUG|A

Which eliminates our stop codon because it shifts the reading frame.

I'm confused.

Maybe it was adding a an A between UAA

I didn't get the question right

I wasn't sure what the difference was between choices A and B

 

[monkeyvokes]

Can anyone explain the reasoning on 136? I got the question correct, but now I realize my reasoning was fallacious and I don't understand that of the explanation.

The stem says a nucleotide was added to the ORF. Okay, fine. The explanation says we should expect a different amino acid at the C-terminus of the translated polypeptide. Why? We're not told where the nucleotide was added into the ORF (it could have been inserted anywhere, not necessarily added to the end), and even if it were added to the end, we wouldn't necessarily get a changed amino acid at the end of the polypeptide.

Furthermore how is it even possible to add in a single nucleotide and not create or eliminate a stop codon?

If the sGP mRNA sequence is this:

AUG|GCU|AUA|CUA|UGA

And we add a single nuc. in the ORF (before the stop codon), we get:

AUG|GCU|AUA|CUA|UUG|A

Which eliminates our stop codon because it shifts the reading frame.

I'm confused.

The open reading frame is the portion of the RNA that doesn't have stop codons. So, if you add a nucleotide there, then you'll likely prolong translation and produce a peptide chain of longer length. As such, you'll likely have a different carboxy terminus.
Also, I think you have to assume it's added at the end since it does not change any stop codons

 

[gettheleadout]

The open reading frame is the portion of the RNA that doesn't have stop codons. So, if you add a nucleotide there, then you'll likely prolong translation and produce a peptide chain of longer length. As such, you'll likely have a different carboxy terminus.
Also, I think you have to assume it's added at the end since it does not change any stop codons

No, you won't. Adding one nucleotide cannot add a single amino acid. The polypeptide length remains the same.

If it's added at the end of the ORF if still changes the stop codon.

Write out a sequence and see.

 

[monkeyvokes]

No, you won't. Adding one nucleotide cannot add a single amino acid. The polypeptide length remains the same.

If it's added at the end of the ORF if still changes the stop codon.

Write out a sequence and see.

well, if you add a nucleotide to the end of the ORF (before the stop codon) then you change the reading frame at the very end. The stop codon is then likely no longer a stop codon.. and you add more amino acids

 

[gettheleadout]

well, if you add a nucleotide to the end of the ORF (before the stop codon) then you change the reading frame at the very end. The stop codon is then likely no longer a stop codon.. and you add more amino acids

Question stem says no stop codon is eliminated.

 

[monkeyvokes]

No, you won't.

Write out a sequence and see.

AAA AAA AAA AAA UAA CCC CCC CCC
normally this would stop at UAA, but if you add one nucleotide to the ORF:
AAA AAA AAA AAA GUA ACC CCC CCC C

doesn't stop where it used to

 

[monkeyvokes]

Question stem says no stop codon is eliminated.

oh right, that does pose a problem. There doesn't seem to be a way in which a nucleotide could be added and still maintain UAA, UAG, or UGA either (since the U would shift to the second position). This is a strange question.

 

[monkeyvokes]

Question stem says no stop codon is eliminated.

I wonder if it should've just said that no stop codon was created?

 

[sunflower18]

I think I might be terribly confused about this question due to the weird way the answer explanation is written...

PS, #20.
The compressive strength of a human bone is about 2 x 10^8 N/m^2. What crushing mass, supported by an upright forearm, would cause a 1% change in length of a 5 cm^2 cross sectional area of forearm bone?

The answer explanation says that the formula given in the passage is rearranged to..
"F = (delta L/L) x E x A. Solving for m gives 0.01 x 5 x 10^-4 m^2 x 2 x 10^8 N/m^2 = 100 kg or 10^2 kg"

First of all, whoa AAMC. How about some parentheses in there so it's not super hard to tell which terms are which. Second of all, I'm assuming that the "5 x 10^-4 m^2" term is from the cross sectional area... But why is it to the -4? Shouldn't it be 5 x 10^-2?? I just feel like I'm missing something but I can't for the life of me figure it out.

Thanks guys 🙂

 

[DocCox]

I think I might be terribly confused about this question due to the weird way the answer explanation is written...

PS, #20.
The compressive strength of a human bone is about 2 x 10^8 N/m^2. What crushing mass, supported by an upright forearm, would cause a 1% change in length of a 5 cm^2 cross sectional area of forearm bone?

The answer explanation says that the formula given in the passage is rearranged to..
"F = (delta L/L) x E x A. Solving for m gives 0.01 x 5 x 10^-4 m^2 x 2 x 10^8 N/m^2 = 100 kg or 10^2 kg"

First of all, whoa AAMC. How about some parentheses in there so it's not super hard to tell which terms are which. Second of all, I'm assuming that the "5 x 10^-4 m^2" term is from the cross sectional area... But why is it to the -4? Shouldn't it be 5 x 10^-2?? I just feel like I'm missing something but I can't for the life of me figure it out.

Thanks guys 🙂

When going from units of cm^2 to m^2 it is a reduction of (10^-2)^2 which leads to 10^-4. If the conversion was from km^2 to m^2 you multiply the number by (10^3)^2 or 10^6. I made the same mistake as you.

 

[sunflower18]

When going from units of cm^2 to m^2 it is a reduction of (10^-2)^2 which leads to 10^-4. If the conversion was from km^2 to m^2 you multiply the number by (10^3)^2 or 10^6. I made the same mistake as you.

Ohhhhhh. That makes so much sense. Okay, thank you so much!! Silly mistakes like this are so costly, argh.

 

[pm1]

Most ionic compounds with strong ionic bonding have which of the following characteristics?

I. Higher melting points than covalently bonded compounds of similar molecular weights
II. Solubility in nonpolar solvents
III. Electrical conductance when dissolved in water

Answer: Both I and III are correct
I got it right, but I am not entirely convinced why I is right.

Rationale:
Strong ionic bonding --> higher intermolecular forces --> lower freezing point / higher boiling point

Since, freezing point = melting point,

Shouldn't the melting point of those strong ionic bonding ionic compounds have a lower melting point?

Thank you!

 

[FeinMS]

I definitely missed #25, but I don't see why C is "irrelevant or incorrect."

Which of the following statements best explains why air resistance is ignored when a compact object falls a very short distance?
B)The speed of the object remains small
C) The area presented to the air is negligible.

The passage says "The upward force is proportional to the square of the air speed of the object and the area presented by the object perpendicular to the motion through the air."

Is B more correct than C because velocity has more effect on the air resistance? I chose C because of the "compact"ness of the object. -_-

107. Difference between maltose and cellobiose.. WTF? Are we expected to know how they look like? After thinking thrice, it seems like the only possible answer is A because C includes D, so both are wrong, and B does not result in a different nomenclature.

 

[FeinMS]

Having a hard time with VR #87.
The authors imply that the Portuguese ambassador applauded the French National Assembly because of genuine sympathy for their ideals. Alternatively, the ambassador's action could be explained as indicating that:
A) living in France, he was in fear of the new revolutionary French government.
B) his life outside of Portugal had broadened his political sympathies.
C) he was at odds with the medieval policies of Queen Maria.
D) he had no strong political commitments one way or the other.
The explanations by AAMC don't satisfy me. AAMC says B is wrong because it's already noted in the passage, so cannot be an alternative explanation. wtf from what letter of "ALTERNATIVELY," do I infer that the answer shouldn't be already in the passage. They also say C is wrong because C implies having genuine sympathy for the ideals of revolts and "imply" doesn't mean "explain." Also wtf because ambassador not liking the policy of divine right monarchy does explain why he support French revolution that is marked as more liberal.

 

[Summerlands]

For #25, I think one way to look at it is to, as you say, notice that air resistance is proportional to v^2, so velocity contributes more to the force of air resistance than surface area does.

I have a question on #23:

The optical power P of a lens is expressed in diopters: P = 1/f, where f is the focal length in meters. Given that the lens-to-retina distance in the human eye averages 2.0 cm, which of the following is closest to the power of the lens of the human eye?

A. 0.05
B. 2
C. 10
D. 40

The correct answer is D (weird, because 1/(2.0 * 10^-2) is really 50, but 40 is the "closest"). How were you supposed to know that the lens-to-retina distance is the focal length as opposed to the radius of curvature? If you were to assume 2.0 cm was the radius of curvature, focal length would be 1 cm, and P would be 100 which isn't an answer, so I didn't have to worry about it for this question, but I am still curious as to what would have led one to determine that "lens-to-retina distance" = f. Thanks!

 

[FeinMS]

Yea that's what I thought about 25.

Image should be projected on the retina. If you set the distance from the object, o, to be infinite so that light rays come in parallel, you can see that 1/i=1/f thus i=f=2cm. Setting o=infinite to derive i=f is like a common example of eye-related question.

 

[gettheleadout]

For #25, I think one way to look at it is to, as you say, notice that air resistance is proportional to v^2, so velocity contributes more to the force of air resistance than surface area does.

I have a question on #23:

The optical power P of a lens is expressed in diopters: P = 1/f, where f is the focal length in meters. Given that the lens-to-retina distance in the human eye averages 2.0 cm, which of the following is closest to the power of the lens of the human eye?

A. 0.05
B. 2
C. 10
D. 40

The correct answer is D (weird, because 1/(2.0 * 10^-2) is really 50, but 40 is the "closest"). How were you supposed to know that the lens-to-retina distance is the focal length as opposed to the radius of curvature? If you were to assume 2.0 cm was the radius of curvature, focal length would be 1 cm, and P would be 100 which isn't an answer, so I didn't have to worry about it for this question, but I am still curious as to what would have led one to determine that "lens-to-retina distance" = f. Thanks!

f = r/2 is only valid for mirrors, just by the way.