Question
Two springs of spring constants k1 and k2 are stretched by the same force. First spring undergoes more extension than the second one. Which of the two springs:
(i) has more value of spring constant
(ii) stores more energy?
Solution
Using Hook's law,
F = kx
i.e., 
Since first spring extends more than second, therefore, 
Energy stored in stretched spring is,
Hence, for the same force applied, the energy stored in spring is directly proportional to its extension.
Therefore, energy stored in first spring will be greater than the second spring.
