Question

A body of mass m attached to a spring of force constant 100N/m is found to stretch the spring to a distance of 0.4m form its equilibrium position. Find the mass of the body.

Answer 1

from Newton’s second law:

$mg=kx\\ m=\frac{kx}{g} = \frac{100\cdot 0.4}{9.81} = 4.08 \text{kg}$