If a force of 100N stretches a spring by 0.1m,find: the workdone in stretching the spring 0.3cm if the elastic limit is not exceeded

Answer 1

the spring constant is ... 1 N/cm

work = 1/2 k x^2 = 1/2 * 1 * 0.3^2 = 0.045 N⋅cm = 45 dyne⋅cm = 45 ergs

Answer 2

Do you mean 0.3 m? If so:
100/0.10 = F/0.3
F = 300 N.

W = F*d = 300*0.3 = 90 Joules.