Question

An iron ball of mass 3 kg is released from a height of 125 m and falls freely to the ground. Assuming that the value of g is 10 m/s², calculate:

1. Time taken by the ball to reach the ground.
2. Velocity of the ball on reaching the ground.

Answer 1

Given: Mass of the iron ball (m) = 3 kg

Initial velocity (u) = 0 m/s

Distance travelled by the ball (s) = 125 m

Acceleration (a)  = g = 10 m/s²

(a) According to Newton’s second equation of motion:

s = `ut + 1/2 at^2`

125 = `0 t +1/2 xx 10 xx t^2`

125 = 5t²

t² = `125/5 `

t² = 25

t = `sqrt25`

t = 5 s

∴ The ball takes 5 seconds to reach the ground.

(b) According to Newton’s first equation of motion:

Final velocity = v = u + a t

= 0 + (10 × 5)

= 50 m/s

∴ The velocity of the ball on reaching the ground is 50 m/s.