A molecule in a gas container hits a horizontal wall with speed `200 ms^(-1)" and angle "30^(@)` with the normal, and rebounds with the same speed. Is momentum conserved in the collision ? Is the collision elastic or inelastic ?

Explanation

Yes, momentum of the molecule + wall system is conserved. The wall has a recoll momentum such that the momentum of the wall + momentum of the outgoing molecule equals momentum of the incoming molecule, assuming the wall to be stationary initially. However, the recoll momentum produces negligible velocity because of the large mass of the wall. Since kinetic energy is also conserved, the collision is elastic.