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

Feb 14, 2016

The net force is made of a gravitational force downward and a spring restoring force upward: $F = m g + k x = 4 \cdot 9.8 + 2 \cdot \left(- 7\right) = 39.2 - 14 = 25.2$ $N$.

#### Explanation:

There are two forces acting on the object, in opposite directions. Let's call 'downward' the positive direction.

The weight force downward is $F = m g = 4 \cdot 9.8 = 39.2$ $N$.

The restoring force upward due to the spring is $F = k x = 2 \cdot 7 = 14$ $N$. This would be written as $- 14$ $N$, because it is in the upward direction.

Add one to the other to find the net downward force, $F = 25.2$ $N$.