Simple Harmonic Motion of a mass hanger

[peaceandlove]

Homework Statement

A 50 g mass hanger hangs moitionless from a partially stretched spring. When a 91 gram mass is added to the hanger, the spring stretch increases by 7 cm. What is the spring constant of the spring (in N/m)? (Assume g = 9.79 m/s2.)

Homework Equations

F=k(delta)L-mg
k(delta)L(sub_e)=mg
(delta)L=(delta)L(sub_e)-y

The Attempt at a Solution

I tried to use the three formulas above to solve for k, however; since I don't know the equilibrium position, I can't find y, which is the displacement of the mass from the equilibrium position.

 

[peaceandlove]

Nevermind!

 

[nlightner]

Without this information, I am unable to accurately calculate the spring constant. It would be helpful to know the initial length of the spring before any masses were added, as well as the final length after the 91 gram mass was added. With this information, I could use the formula (delta)L=sub_e-y to find the displacement from the equilibrium position and then use the formula k(delta)L(sub_e)=mg to solve for the spring constant. Additionally, it would be important to note any external forces acting on the system, such as air resistance, which could affect the accuracy of the measurements. It would also be helpful to repeat the experiment multiple times to ensure the results are consistent and to calculate an average spring constant.