What Goes Down Must Come Up
A ball is thrown down from height
with speed
.
It was observed that the ball rebounds up to exactly the same height.
What is true about the ball's motion?
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1 solution
The ball may have rebounded to the same height, but it had non-zero speed initially, and was at instantaneous rest in the end.
Since the initial and the final heights of the ball are equal, the initial and the final potential energies of the ball are equal. The initial kinetic energy of the ball is positive, whereas the final kinetic energy is zero. Hence, the final total mechanical energy of the ball is less than the initial total mechanical energy.
Where was this energy lost? This energy is mainly lost when the ball makes an inelastic collision with the ground. Some energy is lost as heat and sound during the collision. This results in a decrease in the total mechanical energy of the ball.