# Bullet fired and penetrates a block of wood

1. Homework Statement [/b]

A rifle with a barrel length of 61.54 cm fires a 8.17 g bullet with a horizontal speed of 400 m/s. The bullet strikes a block of wood and penetrates to a depth of 8.9 cm.
What resistive force (assumed to be constant) does the wood exert on the bullet?

Dynamics

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## Answers and Replies

am i even in the right direction? If not where did I go wrong?

Doc Al
Mentor
Did you give the correct attachment?

haha oops good catch give me a second

now its the correct image. Thank you for that.

Doc Al
Mentor
Hint: Use energy considerations.

Is that the only way that we are able to solve this because we haven't gone over engeries in class yet?

Doc Al
Mentor
Is that the only way that we are able to solve this because we haven't gone over engeries in class yet?
No, you can also use dynamics/kinematics. Start by finding the average acceleration.

Am i suppose to assume that the distance the bullet traveled is 70.44 cm? Which is the barrel length+ the depth of the bullet in the wood?

I got the anwser it was 7343.822 N.....only problem is I dont know how I got it I found someone who did this problem online and just plugged my numbers in his equation but it doesn't show how he derived the equation!

I think working on physics so long actually made me worse at it. It was right in front of me I just needed you to remind me of Kinematics! just us xf=xi+(vf^2-vi^2)/2a....then multiply the mass of the bullet by acceleration and that gives me fs.....wow FML