Question

N balls, each of mass M kg, strike per second per unit area a surface normally with velocity V. The pressure exerted by them on the surface will be

• A. 2 MNV${}^2$
• B. 2 MNV
• C. MNV${}^2$
• D. MNV

Answer 1

The correct option is B 2 MNV

'a' is area normal to velocity $V$

By newton's second law,

Force exerted by each ball per second per unit area = rate of change of momentum

=$(MV-(-MV\left)\right)=2MVa$

$\because$ collision with wall is elastic.so, after the collision the ball changes its direction

Force exerted by $N$ balls striking per unit area = 2$NMVa$

Pressure exerted by them on the surface =$\frac{2NMVa}{a}=2NMV$

Hence,option B is correct.