Force needed to extend or compress a spring

Force needed to extend or compress a spring having radius say r and cross-sectional area A by distance say X is proportional to _____.

a. diameter of the spring wire
b. cross-sectional area of the spring
c. change in distance X
d. none of the above

Correct Answer : c. change in distance X

Explanation :

According to Hook's law F = -kX , where k is constant. Therefore force needed to extend or compress a spring is directly proportional to the distance X.