Question

A ball is thrown vertically upwards. It goes to a height 20 m and then returns to the ground. Taking acceleration due to gravity g to be 10 ms^-2 , find : 
the final velocity of the ball on reaching the ground .

Answer 1

Given, maximum height reached, s = 20 m

Acceleration due to gravity, g = 10 m/s²

 

Let v' be the final velocity of the ball on reaching the ground.

Considering the motion from the highest point to ground,

Velocity at highest point = 0 = Initial velocity for downward journey of the ball.

Distance travelled, s = 20m

Using the third equation of motion,

v² -  u² = 2gs

or, v² - 0 = 2 (10) (20) m/s

or, v² = 400 m/s

or, v = 20 m/s