physics
posted by Amanda .
A stone falls from a cliff. It lands on the ground below the cliff after 4.2 seconds. The height of the cliff can be calculated to be what?

It will be the distance that an object falls in 4.2 s, with zero initial vertical velocity component.
You surely know the formula for that:
Y = (g/2) t^2
t = 4.2 s g = 9.8 m/s^2