A 2.0 kg trolley moving at 3.0 m/s collides with a stationary 1.0 kg trolley and they stick together. What is their speed just after the collision?
Answer and explanation
Correct answer: D. 2.0 m/s
- Step 1: Momentum before = 2.0 x 3.0 = 6.0 kg m/s. Step 2. Speed after = 6.0 / (2.0 + 1.0) = 2.0 m/s. Answer: 2.0 m/s. Why not the others: 3.0 m/s ignores the added mass, 1.5 m/s halves the speed as if the masses were equal, and 6.0 is the momentum in kg m/s, not a speed.
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