really annoying EK physics question

[masterMood]

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It's been bugging be like crazy.

Number 82 of chapter 4 page 63.

Seriously? Wtf? Was I the only one who had no clue even after reading the explanation as to why the answer was B.

I understand the concepts of pulleys and levers for one and how they reduce force by compensating by increasing distance yadda yadda yadda...

On 82) the book's solution says that the lever arm for A is longer than that of B in position 1, and the lever arm for A is shorter than that of B in position. I guess this is where my confusion lies.

Anyone care to explain?

 

[tco]

Yeah...This problem bugged me too. I had some kind of witty explaination thought up, but I can't even convince myself that it's correct now.

Anyone else have some insight on this?...Please?

 

[Quantum Chem]

Yes that one got me too initially, but I believe I understand why its B. You have to think of these pulleys as levers and not pulleys. EK actually gives an example of this type of lever on page 61 in red print in the margin. When analyzing the picture move point A and point B to the bottom pulley for simplicity sake. The dots indicate the axis of rotation. Notice how in pos 1 the dot is closer to B and in pos 2 it is closer to A. Now imagine that you want to make equilibrium of a lever the same length as the pulley with a fulcrum where the dot is. If you wanted equilibrium in pos 1 then the force to do B would need to be greater than the force due to A because B has a shorter length (t=f*d*cos(theta)). So the tension due to A is less than B in pos 1. Now look at pos 2 and notice that the dots have switched position, so the force due to A must be greater than B. Hope this helps.

 

[masterMood]

yeah that makes perfect sense quantum chem.

Would you say that this type of question is representative on the MCAT?

 

[masterMood]

nvm figured it out