Three objects A ,   B and C are kept in a straight line on a frictionless horizontal surface. The…

Three objects A, B and C are kept in a straight line on a frictionless horizontal surface. The masses of A, B and C are m, 2m and 2m respectively. A moves towards B with a speed of 9 m s-1 and makes an elastic collision with it. Thereafter B makes a completely inelastic collision with C. All motions occur along the same straight line. The final speed of C is :

  1. 6 m s-1
  2. 9 m s-1
  3. 4 m s-1
  4. 3 m s-1

Solution

Collision between A and B

m×9=mv1+2 mv2 (from momentum conservation)
e=1=v2-v19
⇒v2=6 m sec-1, v1=-3 m sec-1
Collision between B and C

2 m×6=4mv (from momentum conservation)
v=3 m s-1

Asked in: JEE Main 2021 (27 Jul Shift 1)

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