# Car collision Homework Help

1. Sep 16, 2009

### canucklekid

A car starts at rest and accelerates to 7.5 m/s/s towards a 18 wheeler truck headed towards the car at a constant speed of 130 km/h. if they are 500m apart how far from the cars starting position will they collide

im really just having problems solving this i always seem to screw it up i finished all other questions with ease just not this one i feel i am probably making a stupid mistake somewhere in my calculations

btw if there has been a thread similar to this one could you please post a link i did a brief search but didnt come up with anything similar

2. Sep 16, 2009

### Feldoh

What have you tried so far?

3. Sep 16, 2009

### Anden

Hmm, is there no value for the acceleration of the car? Or is the car travelling at 7,5 m/s at the starting point?

4. Sep 16, 2009

### Staff: Mentor

The car's acceleration is given (somewhat unclearly) as 7.5 m/sec2.

5. Sep 16, 2009

### canucklekid

btw my buddy (older friend in university engineering) says the answer is 220m

6. Sep 16, 2009

### canucklekid

the way the question is written to me it sounds like its stopped and instantly is magically able to accelerate to 7.5m/s/s

7. Sep 16, 2009

### Anden

You're right, missed that. :)

What you have to do is try to express the distance travelled by the two vehicles.

8. Sep 16, 2009

### Anden

Your buddy is right, but how do you get there?

9. Sep 16, 2009

### canucklekid

i dont know how he solved it but i want to know if anyone knows please speak up im trying to find out but hes out right now will let you know if i find out but lets try to solve it in the mean time

10. Sep 16, 2009

### kuruman

It would really help you and us if you followed the template for homework help. What are the relevant equations? Hint: There are four and they are collectively called the kinematic equations. Which of these equations is the most likely candidate to help you set up the problem?

11. Sep 16, 2009

### Anden

Ok, set the distance travelled by the car to d1 and distance travelled by the truck to d2.
d1 + d2 = 500, the time travelled by both vehicles is the same. So if you can express the distance travelled with respect to time for both vehicles and then put those two equations together and solve for time, you get the answer.

12. Sep 16, 2009

### canucklekid

yes sorry i thought it was relitivley obvious that the kinematic equations would be used in this thanks for all the help guys