# A bullet, having a mass of 18g and traveling with a velocity of 1200 m/s strikies a

1. Nov 25, 2007

### Freaker

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

A bullet, having a mass of 18g and traveling with a velocity of 1200 m/s strikies a wooden block and pentrates 2.5m. What is the average force exerted by the block on the bullet?

2. Relevant equations

W= F*total distance
W= .5*m*V2^2 - .5*m*V1^2

3. The attempt at a solution

i got the answer -12960 J

2. Nov 25, 2007

### rock.freak667

The question is
Now your answer is in Joules..Force is in Newtons...so you missed something

Consider the law of conservation of energy;
The Kinetic energy lost by the bullet= Work done in moving the bullet 2.5m into the wooden block....
$$E_k=W$$

now you know $E_k=\frac{1}{2}mv^2$ and you know $W=Fs$
so you can find F

3. Nov 25, 2007

### Freaker

em i still don't think i have the right answer 43200 is that right

4. Nov 25, 2007

### rock.freak667

$$\frac{1}{2}*\frac{18}{1000}*1200^2=F*2.5$$
And so
$$12960=2.5F =>F=5184N$$