Physics

Oh God this is dead easy.

Hi, could someone help me with this question please? I think it involves the equations for GPE and KE but I’m struggling on how to do it without being given the mass of the ball.

A ball is dropped from the top of a cliff. By the time it reaches the ground, all the energy in its GPE store has transferred into its KE store. If the ball is travelling at 20 m/s when it hits the ground, what height was it dropped from? (assuming gravitational field strength is equal to 10N/Kg)

When you normally do these sorts of calculations, you usually do something like $\frac12 m v^2 = mgh$.

Clearly then, you can cancel out the mass term.

This should be intuitive - after all, acceleration due to gravity is constant on Earth, if you drop any two things from the same height with air resistance not being a factor, they will fall at the same acceleration & therefore the same velocity.

GPE = m*g*h
KE = mv^2

Equal these equations for the energies and convert it to the height h. g stands for gravitational force, it is g = 9,81 N/kg = 10 N/kg

Thank you!