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Question: Answered & Verified by Expert
A light inelastic thread passes over a small frictionless pulley. Two blocks of masses m=1 kg  and  M = 3 kg, respectively, are attached with the thread and heavy block rests on a surface. A particle P of mass 1 kg moving upward with a velocity of 10 m s-1 collides with the lighter block and sticks to it. The speed of the bigger block just after the string is taut will be [g=10 m s-2]

PhysicsCenter of Mass Momentum and CollisionJEE Main
Options:
  • A 2.5 m s-1
  • B 4 m s-1
  • C 5 m s-1
  • D 2 m s-1
Solution:
2500 Upvotes Verified Answer
The correct answer is: 2 m s-1

Let us assume that just after the collision, the speed of the particle plus 1 kg block is u

2u=1×10u=5 m s-1

After the collision and until the string is taut again, the particle block system is in free fall. So just before the string is taut, the particle plus 1 kg block will be moving downward with a velocity of 5 m s-1 and just after the string is taut, let us assume that the speed of both the blocks and the particle is v, then

2×5=5v

v=2 m s-1

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