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# GPE to KE watch

1. I've been working through some questions for my Physics exam in May, but I've become stuck on one of the questions, can anyone help and explain how they got their answer please?

A stone falls from the top of a cliff 80m high. When it reaches the foot of the cliff, its speed is 38ms-1. Calculate the fraction of the stone's initial GPE that is converted to KE
2. (Original post by ChloeB43)
I've been working through some questions for my Physics exam in May, but I've become stuck on one of the questions, can anyone help and explain how they got their answer please?

A stone falls from the top of a cliff 80m high. When it reaches the foot of the cliff, its speed is 38ms-1. Calculate the fraction of the stone's initial GPE that is converted to KE
You should know a formula for the stones GPE at a height h and a formula for its kinetic energy at a speed v
You are given h and v.

With zero resistance these two values would normally be the same.
In this case there is less KE at the bottom than there was GPE at the top.
(Some energy lost as heat etc but most has been converted to KE.)

The fraction of the GPE converted to KE will be

KE at bottom divided by PE at top.

For example, if there was 100J GPE at the top and 75J KE at the bottom, the fraction converted would be 3/4 (that is 75/100)

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