Answer:
[tex]2.5\cdot 10^{-4}[/tex]
Explanation:
The strain is defined as the ratio of change of dimension of an object under a force:
[tex]S=\frac{\Delta L}{L_0}[/tex]
where
[tex]\Delta L[/tex] is the change in length of the object
[tex]L_0[/tex] is the original length of the object
In this problem, we have [tex]L_0 = 4 m[/tex] and [tex]\Delta L=1 mm=0.001 m[/tex], therefore the strain is
[tex]S=\frac{\Delta L}{L_0}=\frac{0.001 m}{4 m}=2.5\cdot 10^{-4}[/tex]
