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JEE MAIN 2025
02-04-2025 SHIFT-2
Question
The length of a light string is 1.4 m when the tension on it is 5 N . If the tension increases to 7 N , the length of the string is 1.56 m . The original length of the string is $\_\_\_\_$ m.
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Solution
$T=K\left(\ell-\ell_{0}\right)$
$\Rightarrow 5=K\left(1.4-\ell_{0}\right)$
$\Rightarrow 7=K\left(1.56-\ell_{0}\right)$
$\Rightarrow \frac{5}{1.4-\ell_{0}}=\frac{7}{1.56-\ell_{0}}$
$\therefore \ell_{0}=1 m$
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