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 9m/s and makes an elastic collision with it. Thereafter B makes a completely inelastic collision with C. All motions occur along same straight line. The final speed of C is :

Engineering

Physics

Collision

Question

3 m/s

6 ms

9 ms

4 ms

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9m = mv_A + 2mv_B

9 = v_A + 2v_B ….(1)

9 = v_B – v_A .…(2)

Thus v_B = 6 m/s

Collision between B & C

2mv_B = 4mv_C v_C = 3 m/s