A 25 gram bullet (0.025 kg) is fired from a gun with a speed of 210 m/s. If the gun has a mass of 0.91 kg. when rounded to 2 significant figures what is the recoil speed of the gun?

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Answer 1 · 2017-01-10T21:06:09

The gun recoils at #5.8m/s#

This is a conservation of momentum problem. The initial momentum of the system (gun + bullet) is zero, as neither is moving.

There fore, after the gun is fired, the total momentum must still be zero.

#m_g xx v_g + m_b xx v_b=0#

Inserting what we know:

#(0.025)(210)+(0.91)v_b=o#

#v_b = -((0.025)(210))/(0.91) = -5.8 m/s#

The negative sign tells us that the gun travels in a direction opposite to that of the bullet.