20.K is the force constant of a spring. The work done in increasing its extension from
20.K is the force constant of a spring. The work done in increasing its extension from l1 to l2 will be
(a) k(l2 – l1 ) (b) (k/2)(l2 + l1 )
(c) k( l2 2 – l1 2 ) (d) (k/2)( l2 2 – l1 2 )
Answer-d
(3)