AAMC Self-Assessment Physics?

[nabilesmail]

Hey guys, I'm curious, does MCAT usually throw in rotational kinetic energy.

I had a question where it says In the experiment (the wheel is allowed to rotate) and asks how the work of the initial translational energy compares to the work required to stop the wheel

The answer was that it is = to it.

I put it is less than it because You are using energy to stop both the rotational and kinetic energy,

Do I have crappy reasoning here lol

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[rjosh33]

Hey guys, I'm curious, does MCAT usually throw in rotational kinetic energy.

I had a question where it says In the experiment (the wheel is allowed to rotate) and asks how the work of the initial translational energy compares to the work required to stop the wheel

The answer was that it is = to it.

I put it is less than it because You are using energy to stop both the rotational and kinetic energy,

Do I have crappy reasoning here lol

Look again at the question stem. It asks about the change in kinetic energy starting "just before applying the brakes", which lock the wheel into place. So it's no longer rotating for the purposes of the question, and from there it's just W = delta KE.

 

[nabilesmail]

so didn't work have to be done to stop the wheel from rotating?

 

[rjosh33]

so didn't work have to be done to stop the wheel from rotating?

I see what you're saying, but the question tries to take rotational KE out of the equation. By telling us the time "just before the brakes were applied", we're to assume that means the instant that the axle locks and is no longer rotating. Note that in the experiment there were no actual brakes used, but rather there was "some instant the axle of the rolling tire is locked as if brakes were applied".

So basically, the question asked about the work done from that instant until rest. Convoluted, but that's the MCAT for ya.

 

[nabilesmail]

I see, is rotational energy even on the test unless the passage is specifically about it? Thats the second time I took it into account, the other time was a ramp problem, but it said a frictionless ramp, which I forgot about. Maybe I need to just remove the idea of rotation energy, I think I heard somewhere that the MCA doesn't test on it, not sure