Question Detail
Question
A ball with a mass of 7.0 kg strikes a stationary target that has a mass of 2.0 kg. The target flies forward with a velocity of 6.0 m/s, and the ball continues forward at 4.0 m/s. What was the original velocity of the ball in m/s?
Correct Answer
Option A is the correct answer.
Detailed Explanation
Conservation of momentum: m1u1 + m2u2 = m1v1 + m2v2. Here m1=7 kg, m2=2 kg, u2=0, v1=4 m/s, v2=6 m/s. So 7u1 = 7×4 + 2×6 = 28 + 12 = 40. Thus u1 = 40/7 = 5.714 m/s ≈ 5.7 m/s.
Hint
Apply conservation of linear momentum. The total momentum before collision equals total momentum after.