volume_mute

Recoil speed of a gun

publish date: 2023/06/23 20:57:00 GMT+10

volume_mute

A gun has a mass of 10 kilograms and its bullet has a mass of 20 grams.  Suppose that the bullet fires out of the bun barrel with a speed of 300 m/s (about 600 miles per hour).  What is the recoil speed of the gun? ________ m/s

Missing Word

Correct Answer

0.6

Explanation

Answer 

0.6 m/s

Solution

("g" stands for "gun" and "b" for "bullet")

Since the initial momentum = 0, then the total final momentum is zero:

mgvg + mbvb = 0

(10 kg) • vg + (0.02 kg) • 300 m/s = 0

vg = -0.6 m/s

(The negative answer tells us that the velocity is opposite in direction to the 300 m/s.)

Note that mass must be expressed in the same units on each side of the equation.  you can't use "20 g" unless you converted 10 kg to 10000 grams

Reference

Basic Physics: A Self-Teaching Guide

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