NEET Solved Paper 2018 Question 44

Question: 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 / $ on applying a force F, how much force is needed to stretch the second wire by the same amount? [NEET - 2018]

Options:

A) 4 F

B) 6 F

C) 9 F

D) F

Show Answer

Answer:

Correct Answer: C

Solution:

  • For wire 1, $ \Delta \text{l=}( \frac{F}{AY} )3l $ ?(i) For wire 2, $ \frac{\text{F }’}{3A}=Y\frac{\Delta I}{I} $
    $ \Rightarrow $ $ \Delta I=( \frac{F’}{3AY} )I $ ?(ii) From equation (i) & (ii), $ \Delta \text{I=}( \frac{F}{AY} )\text{3I=}( \frac{\text{F }’}{3AY} )I $
    $ \Rightarrow $