A force of 4 pounds is required to hold a spring stretched 0.3 feet beyond its natural length. How much work (in foot-pounds) is done in stretching the spring from its natural length to 0.9 feet beyond its natural length?
First you must find the spring constant, , using .
You are given feet, and lbs.
The negative sign indicates that the spring is in tension.
You are also give feet, which is how much the spring is stretched beyond its natural length.
The negative sign indicates work exerted against the sprink energy.