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.