Question

A boy is rolling a 0.5 kg ball on the frictionless floor with the speed of 20 ms^–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 ?

(1) 19.0 ms^–1

(2) 4.47 ms^–1

(3) 14.41 ms^–1

(4) 1.00 ms^–1

Answer 1

Correct option is (2) 4.47 ms^–1

Given, m = 0.5 kg and u = 20 m/s

Initial kinetic energy (k_i) = \(\frac 12\)mu²

After deflection it moves with 5% of k_i

Now, let the final speed be 'v' m/s, then :