Mass added to a spring to increase period of oscillation

[jomha]

Homework Statement

7. Mass m is oscillating on the end of a spring. How much mass must be added in order for the
period of oscillation to increase by a factor of two?
A.m
B.2m
C.3m
D.4m
E.8m

Homework Equations

f=-kx
w= $$\sqrt{k/m}$$
T = 2$$\pi$$$$\sqrt{m/k}$$

The Attempt at a Solution

since period (T) is proportional to the square root of m and we want 2t, i had 2T=$$\sqrt{m}$$ so 2^2 =4

the given answer is 3 and i don't know how this was chosen

 

[Doc Al]

You found the factor by which the total mass has to increase. But what do they ask for?

 

[jomha]

yeah that makes sense haha 4xm =4m - m that i started with is 3m
thanks a lot it was blowing my mind