# Mass hanging on spring

A 6.00 kg mass suspended from a spring with spring constant, k = 975.0 N/m, extends it to a total length of 0.250 m. Find the total length of the spring when a 15.20 kg mass is suspended from it.
I drew the free body diagram to get,
ma= kx- mg.. since a= 0, kx=mg
solving for x gave me mg/k
So I did (6.00)(9.8)/ 975.0 = .0603 m
Then I did (15.2)(9.8)/ 975.0 = .153 m
I didn't really know where to go from here.. do I subtract the values? Or am I even going about this in the right way?
Thanks

Doc Al
Mentor
Punchlinegirl said:
A 6.00 kg mass suspended from a spring with spring constant, k = 975.0 N/m, extends it to a total length of 0.250 m.
Hint: Find the unstretched length of the spring.

so to find the unstretched length I use Hooke's Law
F= -kd
So it would be like what I had before, mg/k= d
(6.00)(9.8)/ 975 = .0603
since the total length is .250, I do .250-.0603 to get .1990 m.
Is this right?

Doc Al
Mentor
Right idea, but check the arithmetic.

Ok I figured it out. Thanks Doc Al!