A puck moving due east collides elastically with an identical puck at rest on a…
PHYSICS · Single correct · AP · Physics 1: Algebra-based · Linear Momentum · Linear Momentum
Problem
A 0.10kg puck moving due east collides elastically with an identical puck at rest on a frictionless horizontal surface. After the collision the two pucks glide away at right angles to each other. Which of the following best accounts for the 90∘ angle between their paths?
(a) Equal and opposite forces during the collision push the pucks in perpendicular directions, giving them a 90∘ separation.
(b) Since the pucks have identical mass in an elastic collision, they simply exchange velocities; one keeps moving east while the other heads north, so the paths are 90∘ apart.
(c) The simultaneous conservation of linear momentum (a vector) and kinetic energy (a scalar) can both be satisfied only if the two final momentum vectors are at right angles, forming a closed right-triangle equal to the initial momentum.
(d) Because kinetic energy is conserved, each puck must keep the same speed as before the collision, so the only way momentum can still add up is if they move at right angles.