A stone is dropped from a 400 foot high sea cliff at time t

A stone is dropped from a 400 foot high sea cliff at time t = 0. The acceleration due to gravity is given by a(t) = 32 ft/sec². How many seconds after dropping the stone will it hit the water?

Solution

In uniform acceleration the distance covered = 0.5*a*t^2 where a is acceleration. Using this we can say:

distance covered by stone = 0.5*g*t^2

so t = sqrt(2D/g) =sqrt(2*400/32)=5seconds.