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?

1 Answer
David G.
Feb 14, 2016

The net force is made of a gravitational force downward and a spring restoring force upward: #F=mg+kx=4*9.8+2*(-7)=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=mg=4*9.8=39.2# #N#.

The restoring force upward due to the spring is #F=kx=2*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#.

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