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The mass of the gun is:

1. 15 kg
2. 30 kg
3. 1.5 kg
4. 20 kg

Correct answer: 15 kg

Solution

This is a recoil-type centre of mass question. By conservation of momentum, the momentum of the bullet is balanced by the recoil momentum of the gun, which allows the gun’s mass to be determined from the given data. The correct option is 15 kg.

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