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Question: Answered & Verified by Expert
If a string, suspended from the ceilling is given a downward force $F_1$, its length becomes $L_1$, Its length is $L_2$, if the downward force is $\mathrm{F}_2$. What is its actual length?
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Options:
  • A $\frac{L_1+L_2}{2}$
  • B $\sqrt{L_1 L_2}$
  • C $\frac{\mathrm{F}_2 \mathrm{~L}_1+\mathrm{F}_1 \mathrm{~L}_2}{\mathrm{~F}_2+\mathrm{F}_1}$
  • D $\frac{\mathrm{F}_2 \mathrm{~L}_1-\mathrm{F}_1 \mathrm{~L}_2}{\mathrm{~F}_2-\mathrm{F}_1}$
Solution:
2887 Upvotes Verified Answer
The correct answer is: $\frac{\mathrm{F}_2 \mathrm{~L}_1-\mathrm{F}_1 \mathrm{~L}_2}{\mathrm{~F}_2-\mathrm{F}_1}$
$\begin{aligned} &\left(L_1-L\right)=\frac{F_1 L}{A y} ; L_2-L=\frac{F_2 L}{A y} \\ \Rightarrow & \frac{L_1-L}{L_2-L}=\frac{F_1}{F_2} \Rightarrow F_2 L_1-F_2 L=F_1 L_2-F_1 L \Rightarrow L=\frac{F_2 L_1-F_1 L_2}{F_2-F_1} \end{aligned}$

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