Solve Car Crash Problem: 1082667 J Force Applied

[sweedeljoseph]

Homework Statement

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).

Homework Equations

i don't know what would be relevant.
f=m/a
f (cos theta) d

The Attempt at a Solution

the answer from the teacher is 1082667 J but i don't know how youre supposed to find that. i think I am missing some equation. i looked through everything can't 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 wouldn't be right.

thank you!
sweedeljoseph

 

[dirk_mec1]

No...the formula is

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

get it?

 

[sweedeljoseph]

oh yeah i meant that
haha

but how would you use that in the problem? because the mass is given. don't you use that? well you must have to because the answer is 1082667 J and i have no idea how to get that.

 

[dirk_mec1]

oh yeah i meant that
haha

but how would you use that in the problem? because the mass is given. don't you use that? well you must have to because the answer is 1082667 J and i have no idea how to get that.

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?

 

[sweedeljoseph]

yes thank you so much!
i never learned that equation until now. i knew a=delta v/ delta t but that's it. i didnt know it was force.

thanks again
sweedeljoseph

 

[dirk_mec1]

yes thank you so much!
i never learned that equation until now. i knew a=delta v/ delta t but that's it. i didnt know it was force.

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

 

[sweedeljoseph]

yeah i definitely feel stupid but now i get it!