Question

N number of balls of mass m kg moving along positive direction of X-axis, strike a wall per second and return elastically. The velocity of each ball is u m/s. The force exerted on the wall by the balls in newton, is ______.

Options

• 0

• 2mNu

• `"mNu"/2`

• mNu

Answer 1

N number of balls of mass m kg moving along positive direction of X-axis, strike a wall per second and return elastically. The velocity of each ball is u m/s. The force exerted on the wall by the balls in newton, is 2mNu.

Explanation:

The change in momentum of one ball,

Δp = mu - (mu) = 2 mu

The force exerted on the wall by N balls,

F = `"Change in momentum for N balls"/("Total time (t)")`

`= ("2m Nu")/1`    ....(∵ t = 1s)

= 2m Nu