# 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  20 m, what is the net force on the object?

The force due to the spring will be $F = k x = 2 \cdot 20 = 40$ $N$ upward. The weight force of the mass will be $F = m g = 4 \cdot 9.8 = 39.2$ $N$ downward. The net force will be $0.8$ $N$ upward.
(One quick side note: spring constants tend to be quoted in $k g {s}^{-} 2$, but the unit $N {m}^{-} 1$ is equivalent and seems clearer: if the spring constant is $k$, the force it exerts is $k$ $N$ per metre the spring is stretched.)