Simple harmonic motion spring force constant help

[helpmestudent]

Homework Statement

A spring is hung vertically from a support. A mass of 4.5 kg is hung from the lower end of the spring and is slowly lowered a distance of 22.0 cm until equilibrium is reached. This mass is then lowered to a point 15.0 cm below the equilibrium point and is then released, after with the mass vibrates up and down in simple harmonic motion.

It says the answer is 200n/m but I must be doing something wrong!

Homework Equations

k=f/x
f=-kx

The Attempt at a Solution

x=-.15 m
f= 4.5 * 9.8=44.1N
k=f/x, k=44.1/-.15= -294?

what am I doing wrong??

 

[PeterO]

Homework Statement

A spring is hung vertically from a support. A mass of 4.5 kg is hung from the lower end of the spring and is slowly lowered a distance of 22.0 cm until equilibrium is reached. This mass is then lowered to a point 15.0 cm below the equilibrium point and is then released, after with the mass vibrates up and down in simple harmonic motion.

It says the answer is 200n/m but I must be doing something wrong!

Homework Equations

k=f/x
f=-kx

The Attempt at a Solution

x=-.15 m
f= 4.5 * 9.8=44.1N
k=f/x, k=44.1/-.15= -294?

what am I doing wrong??

You calculate the k value from the first part, where the weight force of the 4.5 kg mass extends the spring 22 cm, not the extra 15 cm you extend it to set up the oscillation.