To mop-clean a floor, a cleaning machine presses a circular mop of radius R vertically down with a total…

1. $2 \mu FR/3$
2. $\mu FR/3$
3. $\mu FR/6$
4. $\mu FR/2$

Solution

Net torque $=\sum \mathrm{T}\mathrm{o}\mathrm{r}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{n}\mathrm{ }\mathrm{r}\mathrm{i}\mathrm{n}\mathrm{g}$

$\int d\tau =\underset{0}{\overset{R}{\int }}\mu \times \left(\frac{F}{\pi R^2}\times 2\pi x dx\right)x$
$\tau =\frac{2\mu }{3}FR$

Asked in: JEE Main 2019 (10 Jan Shift 1)

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