How much gravitational potential energy gets converted into kinetic energy?

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I'm doing my Physics coursework for GCSE and my hypothesis is that when a ball is dropped from any height, it's bounce height will always be 60% of the height it was dropped at (so for example, I dropped a ball at 1 metre and it will reach around 60cm when it bounces). I've done the experiment for when the ball is dropped at measurements of 50cm, 60, 70 all the way up to 120cm. So far, I'm right, I thought it will always stay at 60% but my teacher has told me to research it online as she thinks that the percentage should decrease (as in go from 60& and get smaller). I can't find any websites to help!! Can someone please tell me who's right and what's the explanation???

Posted Wed 18th July, 2012 @ 20:18 by Sarina Patel

1 Answer

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Kinetic enery = 1/2(mass x velocity^2)
GPE = mass x 9.8 x height

When the ball hits the ground all the gravitational potential energy is converted into Kinetic energy, because energy is never lost, only changed into different forms. SO at the split-second the ball hits the ground, h=0, so GPE=0 therefore the kinetic energy = the starting GPE. From here, the only thing stopping the ball from bouncing back to the same height is air resistance and friction. Without these forces, the ball would keep bouncing to the same height.

Answered Tue 31st July, 2012 @ 14:51 by Hummi C