Q71 / 90 · JEE Main 2023 (31 Jan Shift 1) · Physics

$100$ balls each of mass $m$ moving with speed $v$ simultaneously strike a wall normally and reflected back with same speed, in time $t s$ . The total force exerted by the balls on the wall is

Solution

Force exerted by each ball is $F = \frac{∆ p}{∆ t}$ , here, $p$ is momentum and $t$ is time.

So, for one ball $F = \frac{m v - m (- v)}{t} = \frac{2 m v}{t}$

Now, total force exerted by the balls on the wall is $F_{n e t} = 100 \times F = \frac{200 m v}{t}$ .

Hence, the correct answer is option: 'B'.