Two blocks M_(1) and M_(2) having equal mass are free to move on a horizontal frictionless surface . M_(2) is attached to a massless spring as shown in figure .Intially M_(2)is at rest and M_(1) is moving toward M_(2) with speed v and collides head- on with M_(2) .

Two blocks M_(1) and M_(2) having equal mass are free to move on a hor

1.	Two blocks M_(1) and M_(2) having equal mass are free to move on a horizontal frictionless surface . M_(2) is attached to a massless spring as shown in figure .Intially M_(2)is at rest and M_(1) is moving toward M_(2) with speed v and collides head- on with M_(2) .
Answer» Whilespring is fully compressed all the KE of `M_(1)` is stored as PE of spring . While spring fully compressed the system momentum is not conserved ,through final momentum is equal to intial momentum . If spring surface on which blocksare moving has friction , then collision cannot be elastic If the surface o which blocks are moving has friction ,then collision cannot be elastic Solution :When `m_(1)` comes in contact with `M_(2),M_(1)` is RETARDED and `M_(2)`is accelerated. (A) The spring will continue to compress until the two blocks acquire will be conserved . (C ) Is spring is MASSLESS wholeenergy of `M_(1)` will be impared to `M_(2) and M_(1)` will be at rest , then (D) Collision is INELASTIC ,even if friction is not involved .