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A block of mass 1 kg moving at 6 m/s collides head-on with a block of mass 2 kg moving at speed v in the opposite direction. After the perfectly inelastic collision the two blocks stick together. For what value of v (in m/s) will the combined system come to rest after the collision?

1. (A) v = 3 m/s
2. (B) v = 4 m/s
3. (C) v = 6 m/s
4. (D) v = 2 m/s

Correct answer: (A) v = 3 m/s

Solution

For the combined mass to be at rest after the collision, the total initial momentum of the system must equal zero (conservation of momentum).

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