Question

A spring requires a load of 2.5 N to increase its length by 4.0 cm. The spring obeys Hooke's law. What load will give it an extension of 12 cm?

Answer 1

Use Hooke's law to find the spring constant, k :

F = kx   ⇒   2.5 N = k (0.040 m)   ⇒   k = 62.5 N/m

Then use the law again to find the force needed to extend the spring by 12 cm = 0.12 m :

F = (62.5 N/m) (0.12 m) = 7.5 N