A 2.5 m long steel rod is put under a stress of 2x10^6 N m−2.

A 2.5 m long steel rod is put under a stress of 2x106 N m−2. Determine by how much
its length will increase

Young's modulus, Y, can be calculated by dividing the tensile stress by the tensile strain:
Y = tensile stress/tensile strain = σ/ ɛ = [F/Ao]/ [∆L/Lo] = FLo/Ao∆L
where
Y is the Young's modulus (modulus of elasticity)
F is the force applied to the object;
A0 is the original cross-sectional area through which the force is applied;
ΔL is the amount by which the length of the object changes;
L0 is the original length of the object.
Thus:-
=>200 x 10^9 = (2 x 10^6)/[∆L/2.5]
=>∆L = 2.5 x 10^-5 m
=>∆L = 0.025 mm

L=(Lf-Li)
l-(lf-li)
-------
li

lf=li
-----------
l

lf= 2.5m
-----------------
2x10^6 N m−2

lf=divide it

It depends on the type of steel the rod is made out of.