A circular disc has a mass of 1 kg and radius 40 cm . It is rotating about an axis p

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6.System of Particles and Rotational Motion

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A circular disc has a mass of $1\ kg$ and radius $40\ cm$. It is rotating about an axis passing through its centre and perpendicular to its plane with a speed of $10\ rev/s$. The work done in joules in stopping it would be ...... $J$

A

$4$

B

$47.5$

C

$79$

D

$158$

Solution

Work done in rotating disc $=$ change in $m=1 k g$

$x=0.4$

So, final $\mathrm{KE}$ is zero as it stops, so work will be Initial $L=K . E=\frac{1}{2} I \omega^{2}$

as,

$\omega=2 \pi f$

$f=10 r e v / s e c$

$\omega=20 x \rightarrow 62.8$

$I=\frac{M R^{2}}{2}=0.08$

so, work done $=\frac{1}{2} \times 0.08 \times(62.8)^{2}$

$158\, J$

Standard 11

Physics

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