A 6 kg rock falls from a cliff. Just before it hits the ground its speed is 24 m/s. From what height did it fall?

Rock starts out at the top of the cliff with maximum potential energy = mgh

As it falls, the potential energy decreases and kinetic energy increases.

When it hits the ground, potential energy will be zero and kinetic energy will be maximum = (1/2) mv²

Do you see that the potential energy at the top of the cliff is equal to the kinetic at the bottom?

mgh = (1/2) mv²

mass cancels out

gh = (1/2) v²

gravity, g = 9.8 m/s²

velocity, v = 24 m/s

(9.8) h = (1/2) (24) ²

9.8h = 288

h = 29.3877551

round to whatever place is specified for the solution.