Acertain spring stretches 3 cm when a load of 15 n is suspended from it. how much will the spring stretch if 30 n is suspended from it (and it doesn't reach its elastic limit)?

Initially, the spring stretches by 3 cm under a force of 15 N. From these data, we can find the value of the spring constant, given by Hook's law:

where F is the force applied, and  is the stretch of the spring with respect to its equilibrium position. Using the data, we find


Now a force of 30 N is applied to the same spring, with constant k=5.0 N/cm. Using again Hook's law, we can find the new stretch of the spring: