Question
A spring of force constant K obeys Hook's law. It requires 4J of work to stretch it through 10 cm beyond its unstretched length.
Calculate:
(i) The value of K.
(ii) The extra work required to stretch it through additional 10 cm.
(Take g = 10 m/s2)
Solution
Work done to stretch the spring, W = 4 J
Distance through which the spring is stretched, x= 10 cm
Work done is given by,
Total work done in stretching the spring through
x' = 20 cm = 
= 
Therefore,
Extra work required = 16 J - 4 J = 12 J
