Q21 of 48 Page 44

Two blocks M1 and M2 having equal mass are free to move on a horizontal frictionless surface. M2 is attached to a massless spring as shown in Fig. 6.10. Initially M2 is at rest and M1 is moving toward M2 with speed v and collides head-on with M2.


Collision is elastic ∴ velocities gets interchanged and K.E. and

linear momentum remains conserved.


when comes in contact with spring, it is retarded by the


spring force and is accelerated by the spring force.


now let’s see the cases,


(a) the spring will compress until two blocks acquire common


velocities .some of the K.E. of is stored as P.E. and


some into K.E. of ∴ (a) is incorrect.


(b)momentum is conserved. option (b) is incorrect.


(c) In head on elastic collision two bodies exchange their


velocities and so finally will come to rest.


option (c) is correct.


(d) ∵ there is loss in K.E. when the blocks collide on rough


surface therefore, collision is inelastic. Option (d) is correct.

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