Question

An elastic cord can be stretched to its elastic limit by a load of 8.0N. Assuming it gives an extension of 250cm when a load of 0.4N is long, what would be the cords length when a force of 2.8N is applied.

Answer 1

$$\Delta l'=\frac{F'}{F}\Delta l\\\Delta l'=\frac{2.8}{0.4}2.5=17.5\ m$$