Question

A force of 2N stretch an elastic material by 30mm what additional force will stretch the material 35mm assume that the elastic limit is not exceeded

Answer 1

The Hooke's law says

$$F=kx$$

Hence, the stiffness

$$k=\frac{F}{x}=\frac{2\:\rm N}{0.03\:\rm m}=66.7\:\rm N/m$$

The additional force

$$\Delta F=k\Delta x\\ =66.7\:\rm N/m\times 0.005\:\rm m=0.33\:\rm N$$