A spring with spring constant $k$ hangs vertically. A mass is hung from the spring and displaces it from its equilibrium position so that it oscillates up and down at a frequency $f_1.$ The first mass is removed and replaced with a mass which is four times the mass of the original one, and sets it to oscillate again.

What will the frequency $f_2$ be now?

$\frac{f_1}{2}$

$4f_1$

$f_1$

$2f_1$

$\frac{f_1}{4}$