Question

the distance that a spring varies directly as the force applied to the spring. A force of 70 pounds is needed to stretch a spring 7 inches. what force is required to stretch the spring 13 inches?

Answer 1

Since the distance that the spring stretchs varies directly as the force applied to the spring, we can use a rule of three to find the force required to stretch the spring 13 inches:

$\begin{gathered} 70\text{ pounds}\to7\text{ inches} \\ x\text{ pounds}\to13\text{ inches} \\ \\ \frac{70}{x}=\frac{7}{13} \\ \frac{10}{x}=\frac{1}{13} \\ x=10\cdot13 \\ x=130 \end{gathered}$

So the force required is 130 pounds.