Are there errors in the MCAT?

[sonnybobiche]

After taking a number of AAMC practice tests, I'm growing extremely concerned that there will be questions on the MCAT that will be counted against me because I give an answer is correct and the AAMC is dead wrong. (Like blatantly, unquestionably wrong, but in a way that someone without a deep understanding of the material would think is correct.) The problem here, of course, is that most people will give an answer that, while incorrect, agrees with the AAMC's choice. Unlike an ambiguous question, where statistically speaking no one is at an advantage, here the advantage will go exclusively to those who know less about the subject. This has happened on a number of occasions on the practice tests, and since these are written by the AAMC, I expect no better from them on the actual exam. The question-challenging system they offer seems purposely useless. I will not be told which questions I got wrong or why I am supposedly wrong, and then I am expected to object within five days of the exam? Totally absurd.
Does anyone else have similar concerns?

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[Tin Man]

After taking a number of AAMC practice tests, I'm growing extremely concerned that there will be questions on the MCAT that will be counted against me because I give an answer is correct and the AAMC is dead wrong. (Like blatantly, unquestionably wrong, but in a way that someone without a deep understanding of the material would think is correct.) This has happened on a number of occasions on the practice tests, and since these are written by the AAMC, I expect no better from them on the actual exam. The question-challenging system they offer seems purposely useless. I will not be told which questions I got wrong or why I am supposedly wrong, and then I am expected to object within five days of the exam? Totally absurd.
Does anyone else have similar concerns?

Erm... which questions exactly are you talking about on the practice MCATs?

It takes some cojones to say that you have SUCH a deeper understanding of the material that the ignorant MCAT people simply don't understand when they're wrong. I've seen some non-AAMC questions that were a little ambiguous (almost exclusively in the VR section), but none that were dead wrong.

There is a much, much higher chance that you're wrong, and possibly that you're overthinking the question and making things more complicated than it needs to be.

 

[deleted74029]

Study hard.

/thread

 

[sonnybobiche]

The most obvious example off the top of my head was on AAMC 9

THOSE OF YOU WHO HAVE NOT TAKEN AAMC 9 STOP READING NOW!!!!


----------------------
The question was about a free wheel and axle rolling on a surface and then stopping due to a brake being applied. The question was how the translational kinetic energy of the wheel-axle system just before the brakes were applied compared to the work done in stopping the wheel-axle system.
Possible answers were
translational KE is more
translational KE is less
translational KE is equal
cannot be determined

My answer was that the translational kinetic energy was less than the total work done because some of that total work had to go into lowering the rotational kinetic energy.
Their (completely wrong) answer was that since Work = change in kinetic energy, the work done on the system is equal to the translational kinetic energy.

 

[latrala2300]

there was a typo on my 8/20 MCAT in one of the answer choices.

 

[Mithril]

The most obvious example off the top of my head was on AAMC 9

THOSE OF YOU WHO HAVE NOT TAKEN AAMC 9 STOP READING NOW!!!!


----------------------
The question was about a free wheel and axle rolling on a surface and then stopping due to a brake being applied. The question was how the translational kinetic energy of the wheel-axle system just before the brakes were applied compared to the work done in stopping the wheel-axle system.
Possible answers were
translational KE is more
translational KE is less
translational KE is equal
cannot be determined

My answer was that the translational kinetic energy was less than the total work done because some of that total work had to go into lowering the rotational kinetic energy.
Their (completely wrong) answer was that since Work = change in kinetic energy, the work done on the system is equal to the translational kinetic energy.
Not to be a jerk, but a relative of mine who has a PhD in physics has read the problem already and agreed with me.

Once you stop translational movement there is no more rotational movement because it's rolling on a surface.

 

[sonnybobiche]

Once you stop translational movement there is no more rotational movement because it's rolling on a surface.

Yes indeed, but that rotational movement doesn't stop for free. Rotational momentum is separate from translational momentum. Thus rotational KE is separate from translational KE. (In fact--and this should demonstrate that I have a modicum of understanding of this field-- each KE is the integral of its respective momentum.)
If you have a box and a ball of equal mass (let's assume the ball's coeff. of static friction equals the box's coeff. of kinetic friction), it takes more energy to get the ball moving at the same speed as the box because part of the energy that you put into it necessarily goes into the ball rotating.

 

[Tin Man]

Yes indeed, but that rotational movement doesn't stop for free. Rotational momentum is separate from translational momentum. Thus rotational KE is separate from translational KE. (In fact--and this should demonstrate that I have a modicum of understanding of this field-- each KE is the integral of its respective momentum.)
If you have a box and a ball of equal mass (let's assume the ball's coeff. of static friction equals the box's coeff. of kinetic friction), it takes more energy to get the ball moving at the same speed as the box because part of the energy that you put into it necessarily goes into the ball rotating.

Right, right. We all have relatives who are super-experts on whatever we believe we're right about.

Without the exact wording of the question, it's pretty difficult to tell you whether or not you screwed up. I don't have access to test 9, but maybe someone else would be kind enough to take a look. It's unlikely your recollection of the problem is going to show any mistake you made in reading it.

 

[mavrik13]

I doubt that any of the MCAT questions you face would end up being incorrect. Either way, there is no point in worrying about it because you will never be able to prove that they are wrong.

I also don't agree with your answer - I don't have an in depth understanding of physics (and can't understand why you would use that knowledge on the MCAT, you are more likely to get yourself in trouble than get an answer right), but you are definitely over thinking the question. Work = change in energy, and it doesn't seem clear to me from your writing of the question that the complexities that you have introduced into the problem are valid. Just my two cents.

 

[mikejungle]

Yeah, I haven't taken number 9, but your thread was too compelling. I guess I'll mark myself off for it.

I'm not quite sure how to think of this. Initially, I thought that if you think about how a brake works, whether it's caliper/rotor, drum, or even a simple brake applied to the exterior of the wheel, it's not like you can apply force strictly perpendicular to the direction it's traveling in, right? The force of friction is used to stop rotational movement, right?

But the definition of rotational force is torque. So is there a formula for work that incorporates both torque and force? If not, then maybe they're right. Otherwise, I think Sonny's right.

If someone knows the answer, please share.

 

[latrala2300]

Once you stop translational movement there is no more rotational movement because it's rolling on a surface.

it stops because of the brake being applied; this, in turn, assumes that there is no frictional force (im doing this from memory, as im too lazy to open up the real test).

sooo dW=dKE + dPE, and dPE = 0.

and i agree that we can all find a relative who agrees with whatever point we're contending that day .

 

[Tin Man]

Again, we need to see the original question.

Given that MCAT questions are vetted as practice questions before regular appearance, an incorrect question would have to have made it through at least one year's worth of testers and still not been detected to show up as a bad question.

 

[sonnybobiche]

People don't seem to believe that the AAMC can be wrong about this, but they most assuredly are. I am not a great chemist or biologist, so I don't question the AAMC in those matters, but there isn't a doubt in my mind about this question, and there are others like it.

I'll provide the question and their reasoning in its exact phrasing. Just FYI there is absolutely nothing remarkable about this wheel and axle stated in the passage. In experiment 2, it's rolling, then it stops because brakes are applied.:
-------------------------------
The initial translational kinetic energy of the wheel system in Experiment 2 (just before applying the brakes):
A) is less than the magnitude of work required to stop the tire.
B) is equal to the magnitude of work required to stop the tire.
C) is greater than the magnitude of work required to stop the tire.
D) cannot be determined from the information given.

The work-energy theorem states that the change in the kinetic energy of a system is equal to the work done on the system. The work done on the system is that needed to stop the tire, and the change in kinetic energy is equal to the initial kinetic energy (because the final kinetic energy is zero). Thus, B is the best answer.
--------------------------------

But my original question was not "why is this the answer," but rather "how common is this?" As I said, I'm not great at biology or chemistry, so I wouldn't notice even if they made an error of this magnitude.

 

[zachjm2]

People don't seem to believe that the AAMC can be wrong about this, but they most assuredly are. I am not a great chemist or biologist, so I don't question the AAMC in those matters, but there isn't a doubt in my mind about this question, and there are others like it.

I'll provide the question and their reasoning in its exact phrasing. Just FYI there is absolutely nothing remarkable about this wheel and axle stated in the passage. In experiment 2, it's rolling, then it stops because brakes are applied.:
-------------------------------
The initial translational kinetic energy of the wheel system in Experiment 2 (just before applying the brakes):
A) is less than the magnitude of work required to stop the tire.
B) is equal to the magnitude of work required to stop the tire.
C) is greater than the magnitude of work required to stop the tire.
D) cannot be determined from the information given.

The work-energy theorem states that the change in the kinetic energy of a system is equal to the work done on the system. The work done on the system is that needed to stop the tire, and the change in kinetic energy is equal to the initial kinetic energy (because the final kinetic energy is zero). Thus, B is the best answer.
--------------------------------

But my original question was not "why is this the answer," but rather "how common is this?" As I said, I'm not great at biology or chemistry, so I wouldn't notice even if they made an error of this magnitude.

I see what you're saying. The AAMC explanation is that work = change in kinetic energy, but kinetic energy would apply to both rotational and translational types. So it can't be possible for work to equal only the translational KE because the rotational KE is unaccounted for. The only way they would be correct would be if they explained it in the passage somewhere about rotational kinetic energy being insignificant or something like that. A wheel would definitely have rotational kinetic energy - as would any spinning or rotating object.

I wonder the same thing - everyone assumes the AAMC is an authority on all things scientific and that they know their material in and out. I can think of times I've wondered if they were making answers up because they didn't match up with anything I learned in my college courses or in the prep books. I just had to guess on the questions.

 

[starstarie]

I think in the end, you just have to suck it up and put it in perspective. If you get an ambiguous question wrong, a lot of other people probably have as well, and maybe that will change the scale in your favor.

In the end, as much as we sometimes think 1 point will change our lives, it kinda wont.

Part of the difficulty in the test is learning to interpret the questions the way the test makers wanted them to be interpreted. Sometimes, you just approach a question wrong, and that sucks. -1.

 

[DrBowtie]

Just an FYI, the people who write the questions are PhDs in their respective fields (I know someone who used to write PS section questions), just like the people who write board questions. There are multiple levels of checks before a question makes it into the scored test bank.

 

[LeoGer]

OP, you should give up right now. You're much too smart for these silly MCAT test makers, and you will be at a sever disadvantage because of this.

 

[FromMathToMed]

Lol

 

[FutureMd08]

The most obvious example off the top of my head was on AAMC 9

THOSE OF YOU WHO HAVE NOT TAKEN AAMC 9 STOP READING NOW!!!!


----------------------
The question was about a free wheel and axle rolling on a surface and then stopping due to a brake being applied. The question was how the translational kinetic energy of the wheel-axle system just before the brakes were applied compared to the work done in stopping the wheel-axle system.
Possible answers were
translational KE is more
translational KE is less
translational KE is equal
cannot be determined

My answer was that the translational kinetic energy was less than the total work done because some of that total work had to go into lowering the rotational kinetic energy.
Their (completely wrong) answer was that since Work = change in kinetic energy, the work done on the system is equal to the translational kinetic energy.

MCAT is correct. Notice that the question says that the INITIAL kinetic energy is equal to ______________.
In this case, we know that K(initial) - Work(friction) = 0
therefore, K(initial) = Work

I see what you are saying, but you seem to be thinking about the final KE which is definitely less than the total work (it is 0).

 

[FutureMd08]

MCAT is correct. Notice that the question says that the INITIAL kinetic energy is equal to ______________.
In this case, we know that K(initial) - Work(friction) = 0
therefore, K(initial) = Work

I see what you are saying, but you seem to be thinking about the final KE which is definitely less than the total work (it is 0).

Basically all of the work that goes into the system to stop it from moving (including the work required to stop the rotational KE) is equal to the INITIAL kinetic energy. This is because in this case KE(initial) + W(nonconservative forces) = KE(final) .....in this case, the final Ke is 0

 

[TBRBiosadist]

Ok back up, Im staring at a copy of AAMC 9 right now, and that question is not on it

EDIT: Just checked the entire PS section, still not on it.

Im calling
Shennanigans

 

[Dreamstoo]

Ok back up, Im staring at a copy of AAMC 9 right now, and that question is not on it

EDIT: Just checked the entire PS section, still not on it.

Im calling
Shennanigans

That 15/14/15 doe. I would take this man's word for it.

 

[TBRBiosadist]

That 15/14/15 doe. I would take this man's word for it.

Idk man. Apparently I'm not as smart as OP, otherwise I would be catching all of these mistakes on the AAMCs.

 

[Dreamstoo]

Idk man. Apparently I'm not as smart as OP, otherwise I would be catching all of these mistakes on the AAMCs.

That 14 VR is abysmal so I do think he has a solid argument.