Finding quantity of energy stored in a spring

[Benzene_ring]

Homework Statement

Hey guys, I'm having some trouble finding the exact quantity of energy storied in this spring problem.
It's like a problem with parts A and B, part A says "Determine the amount of work required to stretch the spring from 0 to 20 cm. I found that to be 125J. For Part B, it says "Suppose that this spring was stretched 7.753 cm. Find the exact quantity of energy stored in the spring.

Homework Equations

I think that the equation that i would use is the one for elastic energy, Ee= 1/2kx^2

The Attempt at a Solution

So far i have Ee= 1/2kx^2

Ee= 1/2k(7.753)^2
I'm not sure if I'm doing this right, or what to do next.

Thanks

 

[Doc Al]

How did you solve part A?

 

[Benzene_ring]

For part A, it had a diagram and the displacement was 20 cm and the force was 12.5N so i calculated 20*12.5/2= 125J

 

[Doc Al]

For part A, it had a diagram and the displacement was 20 cm and the force was 12.5N so i calculated 20*12.5/2= 125J

I assume that the 12.5 N force was the force required to stretch the spring 20 cm. So what's the spring constant?

Careful with units! (Convert distances to standard units: m, not cm.)

 

[Benzene_ring]

I divided 12.5 by 20 and got 0.625, but should i have converted before dividing?

 

[Doc Al]

I divided 12.5 by 20 and got 0.625, but should i have converted before dividing?

Yes. You want k in N/m, not N/cm.

(Note that you'll have to revise your answer for part A.)

 

[Benzene_ring]

Ok, i think i got the right answer.
Ee= 1/2 (625)(0.0078)^2
Ee= 1/2(625)(0.00006)
Ee= 0.01875J

Thank for all the help!

 

[Doc Al]

Ok, i think i got the right answer.
Ee= 1/2 (625)(0.0078)^2
Ee= 1/2(625)(0.00006)
Ee= 0.01875J

Careful! (But you're almost there.)

Check your values for k and for the amount of stretch.