The unstretched length of a spring is 35.0 cm. When a load of 2.0 kg is attached to the lower end of the spring, the spring elongates by 2.0 cm. What is the force constant of the spring? How much work is needed to increase its length from 35.0 cm to 40.0 cm?

Force constant = (2.0 kg)(9.8 m/s^2) / 0.02 m = 980 N/m

Work needed to increase its length from 35.0 cm to 40.0 cm = (980 N/m)(0.05 m) = 49 J