How do I calculate the average deceleration of a car?

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hellothere.
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Sorry about this, must seem a trivial question, but anyways here goes.

A car is traveling at 13ms^1. It is allowed to slow down natrually without appyling the brakes. The distance traveled in coming to rest is 640m.

Show that the average deceleration of the car is about 0.1ms^2.

-------------------

Ok so first of since time aint metioned i used.

v^2 = u^2 + 2as

giving me

v = 0
u =13
a = ?
s = 640

----------------------------------
v^2 = 13^2 + 2(a)640.

v^2= 13^2 +2(640)
___________
a

a * v^2 = 13^2 +2(640)

a = 13^2 +2(640)
__________
v^2

Giving me a very strange answer, no were remotely close to 0.1, I've obviously screwed up the re-arranging or used the wrong formula.

Would like a nudge in the right direction please.
 
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Welcome to PF.

Your equation is ok. But solving it looks not right.

V² = V² + 2*a*x

13² = 2 * a * 640

a = 169/1280
 
LowlyPion said:
Welcome to PF.

Your equation is ok. But solving it looks not right.

V² = V² + 2*a*x

13² = 2 * a * 640

a = 169/1280
Cheers, knew i did something wrong, thanks.