I. Which of the following statements is true about work (only one statement is t

Question

I. Which of the following statements is true about work (only one statement is true)? a) In a collision, the net work experienced by an object is equal to its change in momentum b) The force of kinetic friction never does any work to an object. The net work on an object must always be equal to zero c) d) Work is a scalar. 2. A worker pulls a crate along a floor with a rope that makes a 60° angle with respect to the floor, if the worker pulls with a force of 100 N, find the work done by the person in pulling the crate 8 meters along the floor, a) 400 J b) 693 J c) 800 J d) 3200J 3. Under what conditions is linear momentum conserved? a) Only when there are no net external forces on a system b) Only when there are no net external torques on a system c) Only when non-conservative forces are present. d) None of the above. 4. A person twirls a pocket watch on a chain in a circle with constant speed of co-4 rad/s. If the centripetal acceleration of the watch is 8 m/s, how long is the chain? a) 0.25 m b) 0.5 m c) 2.0 m d) 4.0 m

Explanation / Answer

1. Work is a scalar quantity.

Ans(d)

2. Work done = F.d   ( cross product)

    W = |F||d| cos@

        = 100 x 8 x cos60 = 400 J

Ans(a)

3. If net force is zero. then Fnet = dp/dt = 0

so there will be no change in momentum (p) .

Ans( a)

4. centripetal acc. = w^2 r

8 = 4^2 r

r = 0.5 m

Ans(b)

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