# Spring constant question!

1. Apr 21, 2007

### skittlez411

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

A 1200 kg car rolling on a horizontal surface has speed v=65km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2m. what is the spring stiffness constant of the spring?

2. Relevant equations

K(final)+Us(final)=K(initial)+Us(initial)
1/2mv^2 + 1/2k(delta x)^2= 1/2mv^2 + 1/2k(delta x)^2

3. The attempt at a solution

1/2(1200)(0) + 1/2k(2.2)^2 = 1/2(1200)(18.06) + 1/2k(0)^2
k = 80867.00826 N/m

The answer looks so big that it doesnt make sense to me. I converted the 65km/h to m/s.

thanks,
nicole!

2. Apr 21, 2007

### hage567

Well I didn't check it yet, but think of how much energy a car moving at 65 km/h has! 2.2 meters is quite a small distance for a car to come to a stop!

EDIT: Answer looks OK to me.

Last edited: Apr 21, 2007
3. Apr 21, 2007

### pcdagr8

must be correct
btw...its 18.06^2
i think u hav used it in calculations but missed it here

4. Apr 21, 2007

### skittlez411

yahh i missed it here. i just double-checked my answer.

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