Question

A metal plate of mass 250gm is balanced in air by throwing balls each of mass 25gm vertically up. if the ball rebound at the rate of 20 per second with the same velocity, the velocity with which the balls strike the plate is $(g=10m{s}^{-}2)$

• A. $2.5m{s}^{-}1$
• B. $5m{s}^{-}1$
• C. $10m{s}^{-}1$
• D. $1.5m{s}^{-}1$

Answer 1

The correct option is B $5m{s}^{-}1$

Given that,

Mass of metal plate = 0.25 kg

Mass of each ball = 0.025 kg

Number of balls = 20

Now, the plate is balanced so the force exerted by plate is equal to the force of 20 balls

$mg=20\times \frac{mv}{t}$

$0.25\times 10=20\times 0.025\times \frac{v}{1}$

$v=\frac{0.25\times 10}{20\times 0.025}$

$v=5m/s$

Hence the velocity with which the balls strike the plate is $5$ m/s.