# Help! Force and simple dynamics

1. Jan 26, 2009

### mrnastytime

1. The problem statement, all variables and given/known data
A bullet of mass 0.002 kg initially moving at 510 m/s embeds itself in a large fixed piece of wood and travels 0.78 m before coming to rest. Assume that the acceleration of the bullet is constant.

2. Relevant equations
What force is exerted by the wood on the bullet?

3. The attempt at a solution
In order to find the force, I had to solve for acceleration using the velocity vs function equation: v^2=V0^2 + 2a$$\Deltax$$
a=v^2-V0^2/2$$\Deltax$$
a=0-(510)^2/2(.78)
I plugged in the numbers to the equation f=ma, but it doesnt work. Can anybody help me?

2. Jan 26, 2009

### nvn

It seems to work fine using the equations you posted, which seem correct. Can you show your work, and explain what you mean by the statement, "It doesn't work"?

3. Jan 26, 2009

### mrnastytime

a=0-(510)^2/2(.78)
a=-166730.76
f=0.002kg * -166730 m/s^2
f=-333.46

I entered this answer into my homework online and it is incorrect

4. Jan 27, 2009

### nvn

Nice work; your answer is correct. Should you include units when you enter an answer into your homework on-line? If so, add capital N, for newtons. If that fails, try removing the negative sign (even though the negative sign is correct). If that fails, try entering your answer to only three significant digits, instead of five. If that fails, the on-line program might be wrong or malfunctioning.

Last edited: Jan 27, 2009
5. Jan 27, 2009

### mrnastytime

Thanks! the answer is 333 N