A boy is rolling a 0 . 5 kg ball on the frictionless floor with the speed of 20 m s - 1 . The ball gets deflected by an obstacle on the way. After deflection it moves with 5 % of its initial kinetic energy. What is the speed of the ball now?

Step-by-step solution

Given, m = 0 . 5   kg and u = 20   m   s - 1 Initial kinetic energy k i = 1 2 m u 2 = 1 2 × 0 . 5 × 20 × 20 = 100   J After deflection it moves with 5 % of k i ∴ k f = 5 100 × k i ⇒ 5 100 × 100 ⇒ k f = 5   J Now, let the final speed be ' v '     m   s - 1 , then: k f = 5 = 1 2 m v 2 ⇒ v 2 = 20 ⇒ v = 20 = 4 . 47   m   s - 1