A ball has a mass of 0.25 kg and is moving to the right at 1.0 m/s. It hits a ball of mass 0.15 kg that is initially at rest. After the collision, the 0.15 kg ball moves off to the right with a velocity of 0.75 m/s.

Momentum is conserved. The initial momentum is (0.25 kg)(1.0 m/s) = 0.25 kg·m/s; after the collision, the 0.15 kg ball has momentum (0.15 kg)(0.75 m/s) = 0.1125 kg·m/s to the right. The 0.25 kg ball therefore has 0.25 − 0.1125 = 0.1375 kg·m/s of momentum, giving it a velocity of 0.1375 ÷ 0.25 = 0.55 m/s to the right. The correct choice is C, 0.55 m/s to the right.

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