As shown in Fig. P2.41, a spring having an initial unscratched length of 0 is stretched by a force F applied at its end. The

As shown in Fig. P2.41, a spring having an initial unscratched length of ℓ0 is stretched by a force F applied at its end. The stretched length is ℓ. By Hooke€™s law, the force is linearly related to the spring extension by F = k (ℓ - ℓ0), where k is the stiffness. If stiffness is constant
(a) Obtain an expression for the work done in changing the spring€™s length from ℓ1 to ℓ2.
(b) Evaluate the work done, in J, if ℓ0 = 3cm, ℓ1 = 6 cm, ℓ2 = 10cm, and the stiffness is k = 104 N/m.

Unstretched spring (( - lo)