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 e

Question

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?

TestHub · Accepted Answer

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

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