Question

An object with a mass of `4` `kg` is hanging from a spring with a constant of `2` `kgs^-2`. If the spring is stretched by `4` `m`, what is the net force on the object?

Answer 1

There are two forces acting, a downward weight force `F=mg=4xx9.8=39.2` `N` and an upward restoring force, `F=kx=2xx4=8` `N`. The net force is therefore `35.2` `N` downward.

Explanation:

(insert my usual grumble about the fact that, despite the fact that they are equivalent, `Nm^-1` is a much more sensible unit for the spring constant than `kgs^-2`!)