When a mass of 21 g is attached to a certain

spring, it makes 16 complete vibrations in
4.4 s.
What is the spring constant of the spring?
Answer in units of N/m

1 answer

The period is
P = 2*pi*sqrt(m/k) = 4.4/16 = 0.0275 s

The mass is
m = 0.021 kg

Solve for k by rearranging the first formula