# Homework Help: Kinematics - Find acceleration

1. Sep 3, 2006

### 888

hi,
i need help on a question... if a car stop in a distance of 50m from the speed of 80 km/h how do you find the acceleration is m/s/s? thanks

2. Sep 3, 2006

### Kurdt

Staff Emeritus
What equations of motion do you know? How about rearanging:

$$v^2=u^2 + 2as$$

3. Sep 3, 2006

### 888

i've never used that equation before but all the other equations i know are for constant acceleration or average velocity

4. Sep 3, 2006

### d_leet

Well what equations do you know?

5. Sep 3, 2006

### Kurdt

Staff Emeritus
The equation I put up was for constant acceleration and speeds.

6. Sep 3, 2006

### 888

the equations that i know are: aver. v= v2+v1/2
x2= x1+v1t+.5at^2
v^2=V1^2+2a(x2-x1)
v2= v1+at
those are only for constant acc.

aver acc= v2-v1/t2-t1
aver. vel.=x2-x1/t2-t1

7. Sep 3, 2006

### d_leet

This is the same equation as Kurdt posted above, and it is the one that you should use to solve this problem.

8. Sep 3, 2006

### Integral

Staff Emeritus
Thats just fine because you are looking for the constant acceleration.

9. Sep 3, 2006

### 888

however the question doesn't say it's looking for constant acceleration

10. Sep 3, 2006

### d_leet

But it does say to find the acceleration, and unless you know how to find a non-constant acceleration you should just assume that you are looking for constant acceleration.