a 5kg rock is dropped from a height of 92m. What is the kinetic energy when the rock is 40m from the ground?
I know that the formula is kinetic energy=1/2mv(squared)
but I don't have the time so how would I find the speed, v?
a 5kg rock is dropped from a height of 92m. What is the kinetic energy when the rock is 40m from the ground?
I know that the formula is kinetic energy=1/2mv(squared)
but I don't have the time so how would I find the speed, v?
I don't have the time either, you will have to do it yourself in time for your homework assignment tomorrow.
You can do this in 2 ways, either realise that the loss in potential energy is identical to the gain in kinetic energy, or you can work out the end speed using a SUVAT equation and use the KE equation you have there.
I would say the potential energy way is easier.
Either way, you're going to need to put the work in.
Potential energy at height h = mgh
( m = mass, g = force of gravity)
Kinetic energy at height 92 = 0
Hence loss of potential energy in falling = mg (92 - 40) = 52 mg
Hence Kinetic energy = 52 mg
1/2 mv^2 = 52mg
v^2 = 104g
Substitute value g to get the answer!
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