question_answer 14)

A molecule in a gas container hits a horizontal wall with speed  and angle 30° with the normal, and rebounds with the same speed. Is momentum conserved in the collision ? Is the collision elastic or inelastic?  

Answer:

Momentum is always conserved, whether the collision is elastic or inelastic.   Fig. 6.49   As the wall is heavy, the molecule rebounding with its m speed does not produce any velocity in the wall. Let be the mass of the molecule and M that of the wall. K.E. before collision,   K.E. after collision, As the K.E. is conserved, the collision is elastic.