stretching a spring

Question

Suppose that a force of 20N stretches a spring 0.4 m beyond its natural length. How far will a 40N force stretch the spring?

a. 1.0
b. 0.4
c. 0.2
d. 0.8

Answer 1

Hooke's law says F=-kx where F is the force, x is the distance stretched, and k is the spring constant.

20= -k*0.4

k= -50

40= -50x

x=-0.8

(d) is the answer.