Marvellover65
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I really don't understand this question. How am I supposed to calculate the height without knowing the energy used or the mass.

A ball is dropped from the top of a cliff. By the time it reaches the ground, all the energy in its gravitational potential energy store has been transferred into its kinetic energy store. If the ball is travelling at 20 m/s when it hits the ground, what height was it dropped from? (Assume that the gravitational field strength is 10 N/kg.)
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james113
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This question relies on application of two equations:
1. Gravitational potential energy = mass * gravitational field strength * height = mgh
2. Kinetic energy = 0.5 * mass * (velocity)2 = 0.5mv2

The question tell's us that all of the potential energy is transferred kinetic energy, so we can then set those two equation equal to each other.
mgh = 0.5mv2
Notice how there is m on both sides, thus we can cancel out the mass to get.
gh = 0.5v2
Hope that helped.
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Marvellover65
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(Original post by james113)
This question relies on application of two equations:
1. Gravitational potential energy = mass * gravitational field strength * height = mgh
2. Kinetic energy = 0.5 * mass * (velocity)2 = 0.5mv2

The question tell's us that all of the potential energy is transferred kinetic energy, so we can then set those two equation equal to each other.
mgh = 0.5mv2
Notice how there is m on both sides, thus we can cancel out the mass to get.
gh = 0.5v2
Hope that helped.
Thanks!
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