Is the collision elastic?
Ball A (1 kg, 4 m/s) hits ball B (1 kg) at rest. Afterward, A moves forward at 1 m/s and B at 3 m/s. Which describes the collision?
Answer D: explanation for every choice
A
Kinetic energy dropped from 8 J to 5 J.
B
The balls have different final velocities, so they didn't stick together.
C
Momentum is 4 kg·m/s before and after.
D
Correct. Momentum: 4 before, 1 + 3 = 4 after. Kinetic energy: 8 J before, 0.5 + 4.5 = 5 J after, so 3 J was lost.
TakeawayCheck both: momentum is always conserved, and kinetic energy only in elastic collisions.
Equations usedMomentum and impulseKinetic and gravitational potential energy
Next question →Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp115.