Q 11-08-003NEETNEET 2020Top questionEasy
A wire of length L, area of cross section A is hanging from a fixed support. The length of the wire changes to $L_1$ when mass M is suspended from its free end. The expression for Young's modulus is :
Answer: (D) $\dfrac{MgL}{A(L_1 - L)}$
Concept. Young's modulus is $Y = \dfrac{\text{stress}}{\text{strain}}$.
Step 1. Stress and strain. Stress $= \dfrac{Mg}{A}$; strain $= \dfrac{L_1 - L}{L}$.
Step 2. Young's modulus.
$$Y = \frac{Mg/A}{(L_1 - L)/L} = \frac{MgL}{A(L_1 - L)}$$
Answer. $\dfrac{MgL}{A(L_1 - L)}$ (Option D).
Solution by Sreeraj P, M.Sc Physics