Question

A molecule of gas in a container hits one wall (1) normally and rebounds back. It suffers no collision and hits the opposite wall (2) which is at an angle of ${30}^o$ with wall 1.
Assuming the collisions to be elastic and the small collision time to be the same for both the walls, the magnitude of average force by wall 2. $\left(F_2\right)$ provided the molecule during collision satisfy

• A. $F_1>F_2$
• B. $F_1<F_2$
• C. $F_1=F_2$, both non-zero
• D. $F_1=F_2=0$

Answer 1

The correct option is A $F_1>F_2$

Initial momentum, $P_1=mvcos30$
and final momentum, $P_2=mvcos30$
change in momentum
$\Delta P=-2mvcos30$
$\Delta P=-\sqrt{3}mv$
Force on wall-1
$F_1=\frac{2mv}{\Delta t}$
Force on wall-2
$F_2=\frac{\sqrt{3}mv}{\Delta t}$, so $F_1>F_2$