You drop a rock down a well that is 20 m deep. How long does it take the rock to hit the bottom of the well?

Answer 1

The depth of the well, s = 20 m

The initial velocity of the rock, u = 0 .

Use the law of motion's equation s = ut +(1/2) at² .

In this case the rock dropped  a = g .

Acceleration due to gravity g = 9.8 m/s² .

20 = (0)(t) +(1/2)(9.8)t²

(1/2)(9.8)t² =20

9.8 t² = 40

t² = 40/9.8

     = 4.082

t = 2.02 sec .

The rock reachs the bottom of the well after 2.02 sec .