5. Conceptual questions: A crate slides up an inclined ramp and then slides down

Question

5. Conceptual questions: A crate slides up an inclined ramp and then slides down the ramp after momentarily stopping near the top. There is kinetic friction between the surface of the ramp and the crate. Which is larger in magnitude: the crate's acceleration going up the ramp, the crate's acceleration going down the ramp, or are the magnitudes equal? Explain. a. b. You are pushing a large crate from the back of a freight elevator to the front as the elevator is moving. Assume that there is friction between the elevator floor and the crate. In which situation is the force you must apply to move the crate the smallest and when is it greatest: hen the elevator is accelerating upward, when it is accelerating downward, or when it is traveling at constant speed? Explain.

Explanation / Answer

(a)

The acceleration going up the ramp is greater than the acceleration going down, as it has to overcome gravity.

(b)

Let m be the mass of the elevator.

1. Suppose the elevator is accelerating upward with an acceleration of a. Therefore, the net acceleration of the crate is (a + g). Therefore, total force on the crate is m(a + g).

2. Let the elevator is accelerating downward with an acceleration of a. So, the net acceleration is (g-a).Therefore, total force on the crate is m(g-a).

3. When travelling with constant speed, a = 0. Therefore, the net acceleration of the crate is g. Therefore, total force on the crate is mg.

Force is greatest in case1 and it is smallest in case2.

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