Question

Two balls A and B of same mass and a third ball of mass M are arranged over a smooth horizontal surface as shown in the figure. Ball A moves with a velocity $v_1$ towards ball B and C. All collision are assumed to be elastic. If M <m, the number of collision between the three balls will be :

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

2

The first obvious collision will be between A and B. Since, the mass of A & B is same, A will become stationary after the collision and B will start moving towards C will velocity $v$. The second collision will be between B and C. Since the mass of B is greater than that of C, B will keep moving in the same direction but with a lesser velocity which will be even less than the velocity with which C will be moving in the same direction (rightwards). Thus, there wont be any more collision. Hence, 2 collisions will take place.