Q. A load of 1 kg weight is a attached to one end of a steel wire of area of cross-section 3 ${mm}^{2}$ and Young’s modulus $10^{11}\ Nm^{- 2}$ . The other end is suspended vertically from a hook on a wall, then the load is pulled horizontally and released. When the load passes through its lowest position the fractional change in length is $(g = 10\ {ms}^{- 2})$
A) $0.3 \times 10^{- 4}$
B) $0.3 \times 10^{- 3}$
C) $0.3 \times 10^{3}$
D) $0.3 \times 10^{4}$
Explanation
(a) Young’s modulus,$\ Y = \frac{mgL}{Al}$
⟹ $\frac{l}{L} = \frac{mg}{AY}$
$\therefore\ \ \frac{l}{L} = \frac{1 \times 10}{3 \times 10^{- 6} \times 10^{11}}$
$= 0.3 \times 10^{- 4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.