Question

1.Two objects collide and stick together. The collision [must be, may or may not be, cannot be] elastic.
2.Two objects collide and do not stick together. The collision [must be, may or may not be, cannot be] elastic.
3.A moving object collides with an equal mass object initially at rest. The first object stops after the collision. The collision [must be, may or may not be, cannot be] elastic.
4. A moving object collides with another object of greater mass initially at rest. Both objects move off in the same direction ( but not necessarily the same speed) after the collision. The collision [ must be, may or may not be, cannot be] elastic.

Answer 1

1) As they stick together the velocity of seperation is zero thus e( coefficient of restitution) is zero so the collission is perfectly inelestic

2)If they don't stick together it might be elastic on inelastic

3)By conservation of momentum it can be said that the mass which is at rest now starts to move with same velocity which is possessed initially by other body .which means velocity of approach is equal to velocity of seperation . So perfectly elastic

4) As they are still moving in the same direction the velocity of heavy mass must be less than velocity with which the small mass came( By conservation of momentum). And even the small mass is still moving in the same direction So the velocity of seperation is less than velocity of approach I,e not an elastic collision