question_answer 16)

Two identical ball bearings in contact with each other and resting on a frictionless table are hit head-on by another ball bearing of the same mass moving initially with a speed v. If the collision is elastic, which of the situations shown in Fig 6.50, is a possible result after collision ?   Fig. 6.50  

Answer:

The system consists of three identical ball bearings marked as 1, 2 and 3. Let m be the mass of each ball bearing. Total kinetic energy of the system before collision   Case (i) K.E. of the system after collision   Case (ii) K.E. of the system after collision                 Case (iii) K.E. of the system after collision   Because in an elastic collision, the kinetic energy of the system remains unchanged. Hence, case (ii) is the only possible result of the collision.