Question

Two blocks M₁ and M₂ having equal mass are to move on a horizontal frictionless surface. M₂ is attached to a massless spring as shown in figure. Initially M₂ is at rest and M₁ is moving toward M₂ with speed v and collides head-on with M₂.

(a) While spring is fully compressed, all the kinetic energy of M₁ is stored as potential energy of spring. 

(b) While spring is fully compressed the system momentum is not conserved, though final momentum is equal to initial momentum. 

(c) If spring is mass less, the final state of the M₂ is state of rest. 

(d) If the surface on which blocks are moving has friction, then collision cannot be elastic

Answer 1

Correct option (d)

Explanation:

While spring is fully compressed, the entire kinetic energy of M₁ is not stored as potential energy of spring as M₂ may move. If spring is mass less, also M₁ = M₂, velocities of M₁ and M₂ are interchanged on collision. M₁ comes to rest, instead of M₂. If surface on which blocks are moving has friction, loss of energy is involved. Collision cannot be elastic.