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?

1 Answer
Feb 20, 2016

The force due to the spring will be #F=kx=2*20=40# #N# upward. The weight force of the mass will be #F=mg=4*9.8=39.2# #N# downward. The net force will be #0.8# #N# upward.

Explanation:

There are two forces acting on the object - it's weight force acting downward and a restoring force from the spring acting upward. The magnitudes of these two forces was calculated above, as was the resultant force.

(One quick side note: spring constants tend to be quoted in #kgs^-2#, but the unit #Nm^-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.)