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

As the ball rebounds with same velocity therefore change in velocity = 2u and the mass colliding with the surface per second = nm

Force experienced by the surface $F = m\frac{dv}{dt}$ ∴ F = 2 mnu