JEE Advanced · 2009 · 12 Apr 2009 · Paper 2 · Conservation of Momentum

Three objects A, B and C are kept in a straight line on a frictionless horizontal surface. These have masses

m, 2 m

and

m

, respectively. The object A moves towards B with a speed 9 m/s and makes an elastic collision with it. Thereafter, B makes completely inelastic collision with C. All motions occur on the same straight line. Find the final speed (in

m / s

) of the object

C

Answer: 4

Solution

First collision (A with B, elastic): Using conservation of momentum and energy for elastic collision between masses

m

and

2 m

v_{A}^{'} = \frac{m - 2 m}{m + 2 m} \times 9 = - 3

m/s,

v_{B}^{'} = \frac{2 m}{m + 2 m} \times 9 = 6

m/s. Second collision (B with C, completely inelastic):

2 m \times 6 = (2 m + m) v_{C}

, giving

v_{C} = \frac{12 m}{3 m} = 4

m/s.

JEE Advanced · 2009 · 12 Apr 2009 · Paper 2 · Integer answer

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JEE Advanced · 2009 · 12 Apr 2009 · Paper 2 · Conservation of Momentum

Solution

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