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An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are, 1 kg first part moving with a velocity of 12 m/s and 2 kg second part moving with a velocity of 8 m/s. If the third part flies off with a velocity of 4 m/s, its mass would be:

1. 7 kg
2. 17 kg
3. 3 kg
4. 5 kg

Correct answer: 5 kg

Solution

Using the law of conservation of momentum, the total momentum before and after the explosion must be equal. The momentum of the third part is calculated by balancing the momentum of the first two parts. Solving gives the mass of the third part as 5 kg.

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