A force of 16 lb is required to hold a spring stretched 2 in

A force of 16 lb is required to hold a spring stretched 2 in. beyond its natural length. How much work W is done in stretching it from its natural length to 4 in. beyond its natural length? W = ft-lb

Solution

F = kx k is spring constant

16 = k*2 ---> k = 8 lb/inch

Now Work done = energy of sprong =(1/2)kx^2

= (1/2)(8)(4)^2

= (8*16)/2

= 64 ft .lb