Explanation

(a) When gas is filled in a closed container, it exerts pressure on the walls of the vessel.
According to kinetic theory this pressure is developed due to the collisions of the moving molecules on the walls of the vessels. Whenever a molecules collides with the wall, it return with changed momentum and an equal momentum is transferred to the wall. According to Newton’s law of motion, the rate of change of momentum of the ball is equal to the force exerted on the wall. Since, the gas contains a large number of molecules which are colliding with the walls of the vessel, they exert a steady force on the walls. This force measured per unit area gives pressure, which is same as the molecules are moving in horizontal direction with constant acceleration.
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