Can anyone help with physics? I have a test on monday

Question

1. is it physically possible for the coefficient of friction ever to be greater than one? what would this mean?

2. The moon is accelerating toward the earth. does this mean that it is getting closer to our planet? explain your reasoning

3. an elevator is hoisted by its cables at constant speed. is the total work done on the elevator positive, negative or zero?

4.if the movie 'supergorilla' king kong beats his chest on a frozen frictionless lake, will he go backward? why?

Answer 1

From the top of my head... just so you can't answer your test from my answers...

1. No.  If so, the universe would end.

2. No, it's acclerating AWAY from the earth but the earth's gravity keeps it from getting away, thus the ortbit actually gets bigger.

3. positive

4. what an odd question.  I guess he would only go backward if the force of the fists beating his chest is greater than the air friction.

Answer 2

Sorry but Gary V is leading you astray...

1. Yes friction coefficients can be >1.  Go here and read "Frequent Mistake" subsection:

http://en.wikipedia.org/wiki/Coefficient...

2. Yes & No. The moon is getting closer to the Earth as it's orbit decays over many millenia, but NOT because it is "accellerating" toward the Earth. Sorry to be confusing. The fact that the moon is accellerating toward the Earth merely states that the moon is in free fall (toward the Earth, caused by Earth's gravity), but the moon is moving so fast that it never actually hits. This is the defininition of an "orbit". Think of shooting a bullet parallel to the Earth's surface.  It will immediately start falling (by 1/2 * g * T^2) and eventually hit the ground, UNLESS it's moving so fast that the curvature of the earth comes into play. In this case it will "fall" forever and never land (assuming no air resistance),

3. Work is POSITIVE as you are moving a force (i.e. the weight of the elevator) thru a distance (up). There would be no work done if you moved the elevator sideways because there would be no force opposing the direction of motion.

4. No he'll stay put. The force resulting from the impact of his fist on his chest would be equal and opposite on his fist and chest, so there is no net force. The force driving him backwards (impact on his chest) is offset by the force driving him forward (the impact on his fist). If this were not the case we could build a perpetual motion machine and not worry anymore about $4/gallon gas!

Good Luck on your test...!