PHYSICS · Subjective · AP · Physics 1: Algebra-based · Linear Momentum · Linear Momentum
Problem
Two identical balls E and F, each of mass 0.20 kg, move on a smooth horizontal surface. In the laboratory frame, ball E travels with velocity 4.0 m s⁻¹ along the x-axis while ball F travels with velocity 3.0 m s⁻¹ along the y-axis. They collide elastically.
(a) Determine the velocity of the centre of mass of the system.
(b) Sketch, in the centre-of-mass frame, the momentum vectors of the two balls immediately before collision and explain why the total momentum is zero in that frame.
(c) Using arguments based on symmetry, deduce the directions of the momentum vectors of the two balls immediately after collision in the centre-of-mass frame.
(d) Transform your result back to the laboratory frame and hence find the velocities of balls E and F after the collision.