# Homework Help: Distance Between Stop Signs

1. Oct 5, 2007

### TonkaQD4

A car starts from rest at a stop sign. It accelerates at 4.20m/s^2 for 7.10s, coasts for 2.10s, and then slows down at a rate of 3.10m/s^2 for the next stop sign. How far apart are the stop signs?

2. Oct 5, 2007

### Kurdt

Staff Emeritus
3. Oct 6, 2007

### TonkaQD4

1st Interval

Vf= 0 + 4.20m/s^2(7.10s)
= 29.82m/s

29.82m/s x 7.10s
= 211.72m

2nd Interval

29.82m/s x 2.10s
= 62.622m

3rd Interval

Vf = 29.82m/s - 3.10m/s^2(t)
-29.82m/s = -3.10m/s^2(t)

9.62s = t

29.82m/s - 3.10m/s^2(9.62s)
??

Well, do I have the first two intervals correct?

And I am stuck on the third interval... Does it just equal 29.82m, which means the distance between the two stop signs is 211.722+62.622+29.82= 304.164m

Any help would be greatly appreciated.

4. Oct 6, 2007

### learningphysics

interval 1 is not right...

Remember this is accelerated motion... d = vt doesn't work here unless by v you mean "average velocity"...

what displacement formulas do you have for accelerated motion...

try to apply one here...