Question

A stone is dropped from a 100 m cliff. What is the velocity of the stone after 3 seconds? When
does the stone hit the ground? With what velocity does the stone hit the ground?
(Ignore air resistance.)​

Answer 1

A Stone is dropped from a height of 100 m. To answer the given 3 questions

Given Data:

h= 100 m.

initial velocity($v_{o}$)= 0 m/s

• to find the velocity after 3 sec:

                     $v_{t} = v_{o} +gt\\v_{t} = 0 + 9.81 *3\\v_{t} = 29.43 m/s$

• to find the velocity at which  it hits the ground:

                   $v_{t}^2 -v_{o}^2 =2*g*h\\v_{t}^2-0=2*9.81*100\\v_{t} = 44.29 m/s$

• to find the time at which it hits the ground:

                   $h = v_{o}*t + 0.5 *g*t^2\\100 = 0 + 0.5*9.81*t^2\\t = 4.5 sec$