A ball of mass 0.4 kg falls downward, as shown in the diagram above. Initially y

Question

A ball of mass 0.4 kg falls downward, as shown in the diagram above. Initially you observe it to be 5 m above the ground. After a short time it is just about to hit the ground.

The ball hits the ground and bounces back upwards, as shown in the diagram above. After a short time it is 5 m above the ground again.
During this second interval (between leaving the ground and reaching a height of 5 m) how much work was done on the ball by the gravitational force?
W = J
As a result, the kinetic energy of the ball A) Increases B) Does Not Change C) Decreases

Explanation / Answer

1st part

work done=mghcos(0)=0.4x9.8x5=19.6J

and kinetic energy increases

2nd part

work done=mghcos(180)=-0.4x9.8x5=-19.6J

and kinetic energy decreases

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