A 2 kg ball moving at 5 m/s collides with a stationary 4 kg body. What are their velocities after collision?

The source selects C but omits the collision type and a sign. For a one-dimensional elastic collision, v₁ = −5/3 m/s and v₂ = 10/3 m/s, so the speed magnitudes are about 1.66 and 3.33 m/s.