# Homework Help: Physics 100A Problem about firing a bullet

1. Sep 18, 2009

### calculushelp

I have been working on this problem for an hour and have no clue what to do.
I try to use equations such as

v = v0 + at Velocity as a function of time
delta x = (v0)(t) = 1/2(a)(t^2) Displacement as a function of time
v62 = v0^2 + 2(a)(delta x) Velocity as a function of displacement

but nothing as been working...

A bullet is fired through a board 13 cm thick in such a way that the bulletâ€™s line of the
motion is perpendicular to the face of the board. The initial speed of the bullet is 350 m/s
and it merges from the other side of the board with a speed of 250 m/s.

a.Find the acceleration of the bullet as it passes through the board.
b.Find the total time the bullet is in contact with the board.

thank you to anyone that is will to help.

2. Sep 18, 2009

### rl.bhat

You have to use third and first equation, among the equations which you have written.

3. Sep 18, 2009

### calculushelp

Yeah, I have been using those equations.
But I guess every time my set up is wrong
and I got a crazy answer for acceleration
like -230000. So can yo please show me
how to do it the correct way?

thank you

4. Sep 18, 2009

### Fightfish

Looks correct to me; the acceleration of the bullet is that large - its velocity decreased by 100m/s in just a short span of time approximately of the order of 10^-4 seconds.