How many seconds will it take before the cars meet?

1. Sep 1, 2015

Lana Elcic

1. The problem statement, all variables and given/known data
Two cars are initially 17.50 km apart on a straight road. If the cars are moving toward each other, car 1 with a speed of 7.50 m/s and car 2 with a speed of 10.40 m/s, how many seconds will it take before the cars meet? Round your answer to three significant figures.

2. Relevant equations
Don't know

3. The attempt at a solution
Converted to 17,500 m for the distance apart.
I added 7.50 and 10.40; Then I divided 17,500 by 17.9 seconds
=977.65 seconds

2. Sep 2, 2015

Bystander

You have doubts? Need an organizing/systematic principle?

3. Sep 2, 2015

Lana Elcic

I wanted to see if it was right because I didn't use any formulas, I just kinda thought about it.

4. Sep 2, 2015

haruspex

You have one typo, you wrote 17.9 seconds instead of 17.9 m/s.
If you want to relate your method to a principle, it would be that of relative velocity. Or, equivalently, a change to a different inertial reference frame.