# Car crash problem

1. Nov 10, 2008

### sweedeljoseph

1. The problem statement, all variables and given/known data
A 1015 kg automobile hits a tree at 32 m/s, coming to a complete stop in 0.03 s. What force was applied to the car by the tree? (Take the forward direction of the car as positive).

2. Relevant equations
i dont know what would be relevant.
f=m/a
f (cos theta) d

3. The attempt at a solution
the answer from the teacher is 1082667 J but i dont know how youre supposed to find that. i think im missing some equation. i looked through everything cant really find one that has to do with mass velocity and time for a force. and i have no idea how to make up equations. well i probably could but it wouldnt be right.

thank you!
sweedeljoseph

2. Nov 10, 2008

### dirk_mec1

No...the formula is

$$F =ma =F \frac{ \Delta v}{\Delta t} = 1015 \left( \frac{32-0}{0.03} \right)$$

get it?

3. Nov 10, 2008

### sweedeljoseph

oh yeah i meant that
haha

but how would you use that in the problem? because the mass is given. dont you use that? well you must have to because the answer is 1082667 J and i have no idea how to get that.

4. Nov 10, 2008

### dirk_mec1

Sorry, there should have been a m, let me try it agian:

$$F =ma =m \frac{ \Delta v}{\Delta t} = 1015 \left( \frac{32-0}{0.03} \right)$$

Do you get it now?

5. Nov 10, 2008

### sweedeljoseph

yes thank you so much!
i never learned that equation until now. i knew a=delta v/ delta t but thats it. i didnt know it was force.

thanks again
sweedeljoseph

6. Nov 10, 2008

### dirk_mec1

That's because it isn't force only multiplied with a mass it becomes a force.

7. Nov 10, 2008

### sweedeljoseph

yeah i definitely feel stupid but now i get it!