A surface is hit elastically and normally by n balls per second, each of mass m moving with velocity u. if each ball is made to hit the same surface with velocity 2 u, the force on the surface would become K times. What is the value of K ?

Answer

2

Explanation

Here, initial force, `F_(1)` = rate of change of linear momentum of balls
`=nxxm(-u-u) = -2nm u`
Now force, `F_(2) = n xxm(-2 u - 2 u)`
`=-4 nm u = 2 F_(1)`
`:. K=2`.