A machine gun fires bullets of mass 25 g at 450 m/s, at a rate of 8 bullets every second…

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Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A machine gun fires bullets of mass $25\ \text{g}$ at $450\ \text{m/s}$ , at a rate of $8$ bullets every second. What average force must the gunner apply to hold the gun still?

Need a reminder? The key ideaShow

Momentum is $p = mv$ , a vector. A force acting for a time changes it. The change is the impulse:

\displaystyle J = F\,\Delta t = \Delta p = m(v - u)

Choose a positive direction and give every velocity its sign. For a force that changes with time, the impulse is the area under the force-time graph.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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A machine gun fires bullets of mass 25 g at 450 m/s, at a rate of 8 bullets every second…

The worked solution

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