# Aug. will be here soon... how much do you know?

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#### Mr. Z

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1)The false statement among the following is?

a. a body can have zero velocity and still be
accelerating.
b. a body can have a constant speed and still have
a varying velocity.
c. a body can have a constant velocity and still
have a varying speed.
d. a body can have a negative velocity and still
be positively accelerating.

2)Consider a ball thrown vertically up. Taking air resistance into account, the time to rise compared to the time to fall is...

a. the same
b. shorter
c. longer
d. undetermined as further information is needed

#### u2ecila

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Umm,
1.C and 2.A?

Man, I have been out of school waaaaay to long! Feeling a little brain dead!

<img border="0" title="" alt="[Eek!]" src="eek.gif" />

u2ecila

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Man, I feel really stupid....I'm studying for the Aug. MCAT, too and I don't know the answers to your questions. I've printed them out to ask my physics instructor though. If you know what the answers are, please post them.

#### mpp

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I concur, 1C, 2A

#### CoffeeCat

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Couldn't tell you about the first, but as I understand it, the MCAT never takes into account air velocity! Without air velocity the time up and time down's the same, but including it, it's undetermined because you'd have to take into account surface area, shape, etc.

#### mpp

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But you could assume that the magnitude of the air drag was the same going up as it was going down effectively cancelling out. You are right that if the object were not symmetric and there were more drag in one direction then the other, then it would be undetermined.

#### Mr. Z

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Ok, we're gonna have to do better than those responses or we are gonna be posting 8's in the
physical section

Explanation...
A is true, think of throwing a ball up in the air, when it reaches its max vertical distance it will have a velocity of 0, yet it will be accelerating due to the force of gravity.

B is true, for example, driving in a circle at a constant speed. Velocity is a vector, so it is direction dependant, therefore, driving in a circle would be a case where you are constantly varying the velocity.

D is true, imagine driving backwards (negative velocity) then applying the brakes (positive acceleration).

Question 2 is difficult, I got it wrong also

Explanation...

Air resistance is a frictional force, so on the upward path of the ball,the air resistance is adding to the force of gravity making the (-)acceleration due to gravity seem larger. The ball then reaches vertical max and begins to travel downward, only this time the force due to air resistance is going in the opposite direction of gravity, making the force of gravity seem smaller. Therefore the ball will take longer to travel down then it will going up.

Hope the explanation is clear, if not say so and I'll explain further. I'll post some more ball busters this weekend. Study hard, tick toc, tick toc..

#### wgu

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Hmm I got a weird question:
Are all velocities w/ magnitude=0 the same vector?

#### mpp

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Dang, I feel like dummy...and I have a degree in physics...ouch.

#### Mr. Z

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Chem E major?? what are you thinking man? that's the quickest route to a 2.5 gpa that exists!!

to answer your question... Velocity is a vector, vector's have both magnitude and direction, so if it has no magnitude I would think it's not a vector at all. Can't really think of what it would be?? But, then again I am no physics major. How about it MPP? this one is all you.

#### u2ecila

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Stupid trick questions!

Lol - well at least I won't miss that one on the MCAT. Its been a few year since I took these pre-reqs.

Do any of you have a study plan? How are you doing it?

u2ecila

#### nero

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# 1 is likely a question, but #2 is not likely to be on the MCAT, because like was said earlier, they do not generally account for air resistance because too many factors, size shape can affect it.

nirav

#### mpp

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•••quote:•••Originally posted by nero:
•# 1 is likely a question, but #2 is not likely to be on the MCAT, because like was said earlier, they do not generally account for air resistance because too many factors, size shape can affect it.

nirav•••••I disagree. I think question #2 could easily be on the MCAT. That question does not have anything specific to air resistance, just to the idea of forces as vectors.

#### Mr. Z

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I have to agree with MPP, that could easily be a question on the mcat, no in depth knowledge of air resistance required.

Here's another one...

1. A passenger in an elevator drops a coin at the instant the elevator is ascending at 80 cm/sec. If the acceleration due to gravity is 980 cm/sec-sec, the passenger would observe the acceleration of the coin to be, in cm/sec-sec

a) 1060
b) 980
c) 900

2. The specific heat of water is comparatively large. This explains which of the following

a) Lakes and oceans have moderating effects on
the climate
b) lakes freeze from the top down
c) the heat of vaporization of water is large
d) none of the above

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#### Mr. Z

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MPP is the acronym for the reactive intermediate of 1-methyl-4-phenyl-1,2,3,6-tetrahydropine
(MPTP). It causes lesions in the dopamine producing neurons of the substantia nigra, which leads to Parkinson like symptoms.

In california some years ago, a drug dealer was mixing up his own blend of ecastacy in his basement and then selling it on the streets. Unfortunately, he wasn't a very good chemist, turns out he was carrying out his reactions at too low of a temperature. So, instead of producing pure ecstacy, he produced ecstacy laced with MPTP. Did so in mass quantities, then sold it to a bunch of kids.

When ingested, MPTP can readily cross the blood brain barrier and be transported into the neurons. In the neurons MPTP is metabolized to MPP+, which is highly reactive. It destroys the neurons that produce dopamine. Low dopamine levels lead to Parkinson type symptoms. So all these young children were showing up with what appeared to be parkinson's syndrome, which is typically an late onset disease. These kids will have the affliction for the rest of their lives.

Just wondering if you were doing some research with that compound, thus the screen name? If not, well then now you have some new trivia.

#### u2ecila

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Ok, We will try this again!

1. d - need to know if the elevator is accelerating or not
2. a

u2ecila & crex

#### Mr. Z

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Nicely done, even nailed the trick question (1). I'll have to dig up some more difficult questions to really get you thinking.

#### dtreese

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Not to brag, but just so you know where I'm coming from, I got a 13 on PS (35 total) and taught MCAT physics for Kaplan.

Nice questions to study the discretes. At the same time, you should really familiarize yourself with the passage-type questions, as well.

I found that the AAMC passages were extremely helpful. I only saw one passage on PS that wasn't extremely similar to passages in the AAMC practice passages. They would have the same basic information with different questions, or the information (such as raw data) would be somewhat different with almost identical questions.

Trick questions are not stupid, and they are MCAT classics. These tests are designed to rank premeds, not special ed kindergarteners, so they have to have some real toughies to separate the supersmart from the exceptionally smart. However, if you know the test strategies and have seen lots of similar passages, you don't have to be Stephen Hawking to do well.

In the midst of my proselytizing, I almost forgot why I started this post. Air resistance can and does appear on the MCAT, but only when specifically mentioned. What they will do is give you a formula for air resistance assuming you haven't seen it before and see how well you incorporate it into your current knowledge.

You will see a lot of questions where someone with a lot of upper level science courses will do better. In BS, they tend to use a lot of classic experiments where people who have taken biochem and/or genetics will be familiar with the material, but someone with a more basic background will have to spend a lot more time thinking things out. Of course, even people with fewer science courses can be familiar with these if they do the practice items during the summer.

#### u2ecila

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Woohoo - got both answers this time!

Keep 'em coming Mr. Z!
u2ecila

#### Mr. Z

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Try these on for size...

1) The first law of thermodynamics

a. is equivalent to the conservation of energy
b. requires that a system have a definite internal energy.
c. allows a hot object to get hotter and a cold object to get colder when the two are placed in contact
d. all of the above

2) The kidney removes a fixed percentage of any foreign molecule present in the blood stream. Assuming no cellular absorption, the number of such molecules, after being injected

a. decreases logarithmically with time
b. decreases linearly with time
c. decreases exponentially with time

#### u2ecila

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Thanks, Mr. Z.
Ok, lets see how much we know here!

1. a
2. c

My brain is slowly starting to awaken from its 5 year nap....

u2ecila

#### Tweetie_bird

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let's see...i"m taking a shot in the dark here
1 A
2 B since a "fixed" amount is taken out per unit time.
Am i right?

#### u2ecila

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hey tweetie_bird,
Hmm, I put c on #2 because I thought it meant a fixed percentage, which will be a variable amount based on the amount of foriegn molecules.

I guess it can be ready either way - I hate when I start over analysing questions!!

Mr. Z???

u2ecila
(back to bio MCAT study/surfing the net)

#### Tweetie_bird

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aahh I see what you're saying....could be read in either way.
yo Z.....what does the bible say?

Tweetie

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#### Mr. Z

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Ok here we go.

1. the correct answer is D! that's right D

This question is very difficult, in that it sort of sets you up to fail. But none the less, a thorough understanding of the 1st law would lead you to the correct answer.

The 1st law of thermodynamics (aka law of conservation of energy) states that: Energy can be converted from one form to another, but it cannot be created or destroyed. It implies that we can account for all energy released or absorbed in a physical or chemical change.

a. is correct because heat is a form of energy, the 1st law keeps track of the energy in a thermodyamic system

b. is correct, because the 1st law involves changes in internal energy, before you can have changes in energy you must have energy.

c. seems impossible but in the context of the question is correct. Nothing in the 1st law says this type of transfer is impossible. The 1st law states that the amount of heat removed from the cold object and the amount of heat added to the hot object would have to be the same. That is ALL the 1st law says! It is the 2nd law of thermodynamics that makes this type of transfer impossible. Tricky, I know, it took me awhile to come to terms with it

Question 2 the answer is C

The question says "a fixed percentage", this means that a constant FRACTION of drug will be eliminated per unit time. This is not the same as a fixed amount. With a fixed percentage, the more drug you put in, the more will be eliminated and vice versa. With fixed amount it doesn't matter how much you put in, it will always eliminate the same quantity. So if you plotted a amount of drug eliminated vs. time you will see that the curve starts of with a very large y component (drug amount) at the early time points and decreases exponentially as time goes by and eventually becoming an asymtope with x-axis. This also known as a first order process.

#### Tweetie_bird

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my first shot in the dark and .... <img border="0" title="" alt="[Frown]" src="frown.gif" />

#### CoffeeCat

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•••quote:•••Originally posted by Mr. Z:
• These kids will have the affliction for the rest of their lives.
•••••Actually I've seen a video about that and they planted stem cells in their brains where the dopaminergic neurons were destroyed and they almost completely recovered. The reason that this doesn't work with Parkinsons is that whatever is killing the dopaminergic neurons in the disease also kills the stem cells whereas in this case the drug passed through the system already. Scientists now use the drug to simulate Parkinsons in animals :wink:

#### CoffeeCat

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Hey, anymore questions for us?

#### Mr. Z

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Sorry, I was away enjoying the weekend. Now I get to enjoy the guilt I feel for doing no mcat prep.

1) The mass deficit of a nucleus is

a. the difference between the mass of the protons and neutrons and the mass of the nucleus
b. essentially the binding energy
c. always positive
d. all of the above

2) The fact that the universe is expanding has been verified using the following property of light:

a. superposition
b. diffraction
c. interference
d. doppler effect

3) Consider a kitchen with an electric refrigerator. Leaving the door of the refrigerator open:

a. cools the kitchen
b. does not affect the temperature
c. raises the temperature of the kitchen

#### u2ecila

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Ok, I had to look up mass deficit (aka mass defect/ mass deficiency) because I had no clue what it was! I could not find info on if its positive, but that seem sto follow logically. We'll see...

Here we go:
1. d
2. d
3. c - assuming the room is a closed system, otherwise we need more information

I'm still pondering that 1st law of thermodynamics question that I missed.

u2ecila

#### relatively prime

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I hope you guys realize that those questions are 90% sure to show up with a passage... not by themselves. I've taken the MCAT twice and I've taken like 20+ practice tests (kaplan, PR, and AAMC) and I'm telling you that the stand-alones aren't usually that hard at all... those or the types of questions that comes with passages.

just FYI

#### Mr. Z

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Passages??? You mean it's not all true and false? Damn it! I knew I shouldn't have went with that discount review book! J/k

I think most people on this board, including myself, are very familiar with the format of the mcat. These questions are not intended to mimic the stand alones, nor the passage questions. They are just to get you thinking about concepts and thinking about them in an unfamiliar context, and also to maybe highlight a topic or two that you may have forgotten to cover etc. etc. etc...
I think it has worked already, check the post above about mass deficit.

If people don't like the questions, or are finding them unhelpful, let me know, please!

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please post answers/explanations for those latest problems....I'm getting very curious to know.

#### Mr. Z

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1) D the mass of a nucleus is always less than the total mass of the nuclei's individual protons and neutrons. This difference in mass is called the mass deficit. The mass deficit can be converted into energy via the famous E=MC^2 equation to give you the binding energy of an atom.

2) D This is pretty straight forward... if the universe is expanding, i.e. moving away from the observer, it has the effect of decreasing the observed frequency. This would be seen as a "red shift" in the light. If the universe was contracting it would be a blue shift, b/c of the observed frequency being greater. Light is subject to the doppler effect the same as sound is.

3) C The room temp would increase. The compressor itself would give off heat in the course of its action.

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Thanks Mr.Z.....keep em coming.

#### Mr. Z

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The fun continues...

1) T1 decays by the emission of beta particles (1/2 life of 3.1 minutes). As a result, Pb is produced. After 9 mins, an initially pure sample of of T1 contains 7 g of Pb. What was the approximate mass of the original sample?

a) 7 g
b) 8 g
c) 28 g
d) 32 g

2) Constant accelerated motion is always characterized by:

a) a linearly increasing speed
b) a straight line of the v vs. t graph
c) an increase in distance proportional to the square of the time
d) a horizontal graph on the v vs. t graph

3) Consider a piece of rubber and a piece of hemp rope. The young's modulus

a) is the same for both
b) is larger for the rubber
c) is larger for the rope
d) depends on the relative length of each

4) used to be thought that heat was a substance, called caloric, which flowed from one object to another. The best evidence against this idea is that:

a) heat flows from hot objects to cool ones
b) it is possible to remove any amount of heat from an object without changing the object
c) the heat exchanges in calorimeter experiments are balanced
d) heat can be transfered by convection

#### relatively prime

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Mr Z: That's what I figured... I just didn't want someone seeing this board who doesn't know anything about the MCAT being like "oh my God!"
That's what happened to me when I first came to SDN and saw an MCAT thread that posted questions... I totally freaked out... I just figured I'd try and save someone that tramatic experience.

#### Mr. Z

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Relatively,

good point, I should have made mention of that when I started the thread. God knows the damn exam is confusing enough without any added complexities coming from a discussion thread.