A pair of balls (both of mass m) are sliding along a long, horizontal, frictionless groove towards a stationary third ball (also of mass m), as shown in the following diagram. The coefficient of restitution of the balls is 0.4. a. Explain why the sum of the velocities of the three balls must always be 8 m/s. b. By calculating the velocities of the balls after every collision, demonstrate that B hits C, then A hits B and finally B hits C again, after which there will be no more collisions