Which one of the following is not an example of work being done? . a. the moon orbiting earth . b. pushing a box from the bottom of a hill to the top of the hill . c. pulling a sled across a field covered with snow . d. lifting a bookbag off the floor

The moon orbiting Earth

Explanation:

- The work done is given by:

                            W = integral (F).ds

In words, It is the dot product of Force in the change displacement. In every case the the force is in the direction of displacement.

Except, when the moon is orbiting the earth, the change in displacement is zero. Hence, the work done is zero as ds = 0.  

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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it is the second option.