Question

A ball is dropped from a height of 20 m. A second ball is thrown down wards from the same height after one second with initial velocity u. If both the balls reach the ground at the same time, calculate the initial velocity of the second ball. (Take g=10 m/s2)

Answer 1

Given:

height, h = 20m

acceleration due to gravity, g = 10m/s²

Initial velocity of first ball = 0m/s

Let the time taken by the first ball be t,

=> h = gt²/2

=> t = (2h/g)^1/2

= 2s

=> time taken for the second ball to reach the ground, t' = 1s

=> h = ut' + (gt²')/2

=> u = 15m/s