If the force constant of a wire is $K,$ the work done in increasing the length of the wire by $l$ is
A$Kl/2$
B$Kl$
C$K{l^2}/2$
D$K{l^2}$
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C$K{l^2}/2$
c (c) $K = \frac{F}{l}$and $W = \frac{1}{2}Fl = \frac{1}{2}Kl \times l = \frac{1}{2}K{l^2}$
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