- A$\frac{{\mu {l^2}}}{{12}}$
- B$\frac{{\mu {l^2}}}{6}$
- C$\frac{{\mu {l^4}}}{{12}}$
- ✓$\frac{{\mu {l^4}}}{6}$
Mass per unit area $=$ $\mu$
Total mass $M=\mu l^{2}$
Now, the moment of inertia is $I=\frac{M R^{2}}{12}$
By perpendicular axis theorem $I=I_{x}+I_{y}$
$I=2 I_{x}$
$I=2 \times \frac{\mu l^{2} \times l^{2}}{12}$
$I=\frac{\mu l^{4}}{6}$
Hence, the moment of inertia of a square sheet is $\frac{\mu l^{4}}{6}$
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[$A$] The amount of energy radiated by the body in $1$ second is close to $60$ Joules.
[$B$] If the surrounding temperature reduces by a small amount $\Delta \mathrm{T}_0<<\mathrm{T}_0$, then to maintain the same body temperature the same (living) human being needs to radiate $\Delta \mathrm{W}=4 \sigma \mathrm{T}_0^3 \Delta \mathrm{T}_0$ more energy per unit time.
[$C$] Reducing the exposed surface area of the body ($e.g$ by curling up) allows humans to maintain the same body temperature while reducing the energy lost by radiation.
[$D$] If the body temperature rises significantly then the peak in the spectrum of electromagnetic radiation emitted by the body would shift to longer wavelengths.

