Question

A 4.5-kg block is hung from a spring causing the spring to elongate 12 cm. With what period will the spring oscillate if the spring was stretched 15 cm and released?

Answer 1

for your other mass/spring problem I derived:

(2 pi f)^2 = k/m

same here
to get k:
F = weight = 4.5 * 9.81 = 44.1 N
deflection = .12 m
so k = 44.1/.12

now solve for f = (1/2pi)sqrt(k/m)
and
T = 1/f