n small balls, each of mass m impinge elastically each second on a surface with a velocity u , then the force experienced by the surface in one second, will be:

Question

n small balls, each of mass m impinge elastically each second on a surface with a velocity u , then the force experienced by the surface in one second, will be: (A) 4 mnu (B) 2 mnu (C) 1.5 mnu (D) 0.8 mnu

Tardigrade Admin · Accepted Answer

Force experienced by the surface is equal to change in momentum in one second.
From Newton's second law of motion the rate of change of momentum of a body is equal to the external force applied on the body and the change is momentum always takes place in the direction of the force.
Momentum of ball before inpact

= m u

Momentum after inpact

= - m u

Change in momentum

= m u - (- m u) = 2 m u

.
Change in momentum due to

n

balls in one
second is

= 2 mn u

.
Change of momentum

=

Force experienced per second

= 2 mn u

Q. n small balls, each of mass m impinge elastically each second on a surface with a velocity u , then the force experienced by the surface in one second, will be:

4 mnu

2 mnu

1.5 mnu

0.8 mnu

Q. $n$ small balls, each of mass $m$ impinge elastically each second on a surface with a velocity $u$ , then the force experienced by the surface in one second, will be: