The first one is the actual question:

A force of 10 lb is required to hold a spring stretched 8 in. beyond its natural length. How much work W is done in stretching it from its natural length to 14 in. beyond its natural length? W = X 245/24 ft- lb Solution or Explanation We have 10 = f(x) = kx = (2 k 8 inches = _ foot , so k = 15 1b/ ft and f(x) = 15x. Now 14 inches = - foot, so we get the following. W = 67 15x dx = 2x2 7/6 = 245 .ft-lb 24A force of 14 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 5 in. beyond its natural length? W = 7.29 x ft-lb Need Help? Read It Watch It Master It