If n balls hit elastically and normally on a surface per unit time and all balls of mass m are moving with same velocity u, then force on surface is

Question

If n balls hit elastically and normally on a surface per unit time and all balls of mass m are moving with same velocity u, then force on surface is (A) mun (B) 2 mun (C) (1/2) m u2 n (D) m u2 n

Tardigrade Admin · Accepted Answer

As collision is elastic, velocity after the collision will be -u So using F=(d p/d t) =n(m u-(-m u) =2 n m u

Q. If $n$ balls hit elastically and normally on a surface per unit time and all balls of mass $m$ are moving with same velocity $u$ , then force on surface is

$m u n$

$2 m u n$

$\frac{1}{2} m u^{2} n$

$m u^{2} n$

As collision is elastic, velocity after the collision will be $- u$
So using $F = \frac{d p}{d t}$
$= n (m u - (- m u)$
$= 2 nm u$

Q. If n balls hit elastically and normally on a surface per unit time and all balls of mass m are moving with same velocity u, then force on surface is

mun

2mun

21​mu2n

mu2n