JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Work, Power & Energy

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?

(A) $14.41 ms^{- 1}$
(B) $19.0 ms^{- 1}$
(C) $1.00 ms^{- 1}$
(D) $4.47 ms^{- 1}$ ✓ Correct

Answer: (D)

Solution

The initial kinetic energy is

K_{i} = \frac{1}{2} (0.5) (20)^{2} = 100 J

Only

5%

survives the deflection, so

K_{f} = 5

J and

\frac{1}{2} (0.5) v^{2} = 5 \Rightarrow v^{2} = 20

The speed of the ball after deflection is

20 = 4.47 m s^{- 1}

JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Single correct option

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