# Problem with running car

1. Aug 12, 2013

### PerryKid

1. The problem statement, all variables and given/known data

A car starts to run from rest with acceleration 0.5 m/s2. How long does it take to travel distance 60m? [sic] (I have a Russian teacher for AP Physics)

2. Relevant equations

V= (Xf-Xi)/(Tf-Ti)
ΔX= Vi*T+(1/2)aT2

3. The attempt at a solution

I tried to find velocity, but that didn't really work out.
0.5 m/s2=Vf-Vi/Tf-Ti
Is there an equation or some way that I can directly solve for distance from acceleration?

Last edited: Aug 12, 2013
2. Aug 12, 2013

### BruceW

ΔX= Vi*T+(1/2)aT2
from this equation, you are close to the answer already. What does Vi stand for here? and so what is its value?

3. Aug 12, 2013

### PerryKid

Vi stands for initial velocity. It has an unknown value.

Last edited: Aug 12, 2013
4. Aug 12, 2013

### Staff: Mentor

What does "A car starts to run from rest" mean to you with regard to the car's initial velocity?

5. Aug 14, 2013

### PerryKid

I got it in class.

This was the process:

(Vf-Vi)/(Tf-Ti)=A

Or rather... ΔV/ΔT=A

Since A= 0.5 m/s2, A=(0.5 m/s)/1 s

Thus, V= 0.5 m/s

The ratio is the same and thus (0.5 m)/(1 s)=(60 m)/(x s)

60 m*s = 0.5x m*s

120 s

:P

Thank you for putting up with me and with the odd grammar.

6. Aug 14, 2013

### Staff: Mentor

That can't be right. After 120 seconds with an acceleration of 0.5 m/s2 the car will have traveled 3.6 kilometers...that's more than slightly larger than 60 m.

What you've sort of calculated is the time it takes for the velocity to reach 60 m/s. Unfortunately, velocity is not the same as distance

Go back to your second equation (the one for ΔX) and take another look at the posts by BruceW and Chestermiller.

7. Aug 14, 2013

### SteamKing

Staff Emeritus
How fast do you run when you are at rest?