So I checked out the physics class I was taking on ratemyprofessor.com and John Ross was the guy who was teaching it. He had good reviews, so I figured I'll take his class. Well, a TA is teaching it, and I won't name the person, but he isn't really a teacher--even with his PhD in astrophysics. Needless to say, I'll probably be needing quite a bit of help. Thanks in advance for anyone who does help.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A 12g bullet is fired in a 87.8g block of wood at rest on a horizontal surface and stays inside. After impact, the block slides 9.8m before coming to rest. The acceleration of gravity is 9.8 m/s^2

If the coefficient of friction between the surface and the block is .5, find the speed of the bullet before impact.

Answer: 81.5033 m/s

2. Relevant equations

Normal Force = mg

Work = Distance * Force

Another one with velocity in the variable

3. The attempt at a solution

The farthest I got was finding the frictional force that opposes the motion of the block.

Normal Force = (.012+.0878)(9.8) = .97804 in the upward direction

Friction Force = (.5)(.97804) = .48902

I suppose I could turn that into work, which would be:

Work = (.48902)(9.8) = 4.79240 in the westward direction

That gives me the force that opposes the motion of the block, but I don't think that gets me anywhere closer to the velocity. This is where I am stuck, and although I know the answer, I will have to know how to do this for the test. Any guidance will be much appreciated.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Impact of a Bullet into a Block

**Physics Forums | Science Articles, Homework Help, Discussion**