Question

n small balls each of mass m impinge elastically each second on a surface with velocity u. The force experienced by the surface will be

• A. mnu
• B. 2 mnu
• C. 4 mnu
• D. $\frac{1}{2}mnu$

Answer 1

Answer: (B)

2 mnu

Answer 2

$\overrightarrow{F} = \frac{d\overrightarrow{p}}{dt} =$ Rate of change of momentum

As balls collide elastically hence, rate of change of momentum of ball = $n\lbrack mu - (mu)\rbrack$ = $2mnu$i.e. $F = 2mnu$