Q. Two wires are made of the same material and have the same volume. The first wire has cross-sectional area A and the second wire has cross-sectional area 3A. If the length of the first wire is increased by $\Delta l$ on applying a force F, how much force is needed to stretch the second wire by the same amount ?
A) 4 F
B) 6 F
C) 9 F
D) F
Explanation
[Solution] Same volume: $L_2 = L/3$. $F = YA\Delta l/L$, so $F_2 = Y(3A)\Delta l/(L/3) = 9F$. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.