JEE MAIN - Physics (2022 - 24th June Morning Shift - No. 26)
A metre scale is balanced on a knife edge at its centre. When two coins, each of mass 10 g are put one on the top of the other at the 10.0 cm mark the scale is found to be balanced at 40.0 cm mark. The mass of the metre scale is found to be x $$\times$$ 10$$-$$2 kg. The value of x is ___________.
Answer
6
Explanation
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Let $\mathrm{M}$ be the mass of the meter scale.
The weight $\mathrm{Mg}$ of the scale acts at $50 \mathrm{~cm}$ mark.
Finally after putting two coins on the meter scale, balancing the torques about the knife edge, we get,
$20 g \times 30=\mathrm{Mg} \times 10$
$$ \begin{aligned} M & =60 \mathrm{~g} \\\\ & =60 \times 10^{-3} \mathrm{~kg} \\\\ & =6 \times 10^{-2} \mathrm{~kg} \\\\ & =x \times 10^{-2} \mathrm{~kg} \end{aligned} $$
On comparing, we get $x=6$
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