# Force Needed to Stop a Flying Bullet

1. Nov 20, 2011

### IBdoomed

A bullet of mass 0.0025 kg moving at 470 m/s
impacts a large ﬁxed block of wood and travels
6.2 cm before coming to rest.
Assuming that the deceleration of the bullet
is constant, ﬁnd the force exerted by the wood
on the bullet.

I know force= mass * acceleration but i don't know how the distance plays into the solution. Any kind of kinematics formula would be sufficiently helpful!

2. Nov 20, 2011

### PeterO

Choose wisely from the sets of equations shown in the first two sections of this wikipedia posting.

http://en.wikipedia.org/wiki/Equations_of_motion

3. Nov 20, 2011

### IBdoomed

i was trying to use v^2= u^2+2as
but the answer i am getting is wrong....
is there a different formula you suggest?

4. Nov 20, 2011

### PeterO

That is certainly the one I would use.

Were you converting everything to metres and seconds?

This formula will only calculate the acceleration of course - you need at least one more step to get the force.

5. Nov 20, 2011

### IBdoomed

nevermind. i was not converting my answer into kN.... thank you so much!