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A machine gun fires bullets of mass 10 g each at a rate of 60 bullets per minute, the muzzle speed of each bullet being 100 m/s. What is the thrust (reaction force) experienced by the person who holds the gun steady?

1. 1 N
2. 6 N
3. 10 N
4. 60 N

Correct answer: 1 N

Solution

60 bullets/min = 1 bullet/s, so dm/dt = 0.01 kg/s; thrust F = v*(dm/dt) = 100*0.01 = 1 N.

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