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**Physics** on
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A new type of spring is found where the spring force F is given by F=-kx + bx^2 where k=400 N/ m and b=100 N/m^2 and x is the expansion (or compression) of the spring from its equilibrium position. The spring is attached to a point mass of 1 kg sitting on a horizontal frictionless table.

A. Find he work done by the spring acting on the attached mass when the mass is pulled by a person from x=0 to x=-0.5m.

B. If the mass is released from rest by the person at the -0.5 m point, what is the speed of the mass at x=0?