Andrew and stella are at the top of a cliff dropping rocks. Stella drops a rock and it hits the water after 7 seconds. How tall was the cliff

Question

Andrew and stella are dropping rocks from a cliff. Stella drops a rock and it hits the water after 7 seconds. How tall was the cliff?

Answer 1

Neglecting air resistance, and with the rock released from rest, the vertical travel distance (i.e. the height of the cliff) is

 

h = gt²/2 = (9.8 m/s²)(7s)²/2 = 240.1 m

 

If you want the height in feet, use g = 32 ft/s².

 

h = (32 ft/s²)(7s)²/2 = 784 ft