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**[SOLVED] Momentum of bullet fired into target**

**In a ballistics test, a 23.0 g bullet traveling horizontally at 1100 m/s goes through a 40.0 cm-thick 250 kg stationary target and emerges with a speed of 800 m/s. The target is free to slide on a smooth horizontal surface. What average force does the bullet exert on the target?**

**Using kinematic equations, I was able to solve for the acceleration, and use that to solve for the time, which ended up being 4.21*10^-4. I then used the equation F_avg = m(v_f - v_i) / t in an attempt to solve for average force. I plugged in values for the bullet (m=0.023m v_f=800m/s v_i=1100m/s, t = 4.21*10^-4. and ended up with an answer of 17800 N.**

This answer is wrong. I also came up with 16,400N, 16,340N and 16,300N, all of which tell me I am off by an "additive constant." Am I using the right equation to solve for F_avg, but just the wrong values for mass and velocity? And what is an additive constant?

This answer is wrong. I also came up with 16,400N, 16,340N and 16,300N, all of which tell me I am off by an "additive constant." Am I using the right equation to solve for F_avg, but just the wrong values for mass and velocity? And what is an additive constant?