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A circular platform is mounted on a frictionless vertical axle. Its radius \mathrm{R=2 \mathrm{~m}} and its moment of inertia about the axle is \mathrm{200 \mathrm{kgm}^2}. It's initally at rest. A \mathrm{50 \mathrm{~kg}} man stands on the edge of the plate form and begins to walk along the edge at the speed of \mathrm{1 \mathrm{~m} / \mathrm{s}} relative to the ground. Time taken by the man to complete one revolution is -
 

Option: 1

\mathrm{\pi s}
 


Option: 2

\mathrm{\frac{3 \pi}{2} s}
 


Option: 3

\mathrm{2 \pi \: \mathrm{s}}
 


Option: 4

\mathrm{\frac{\pi}{2} s}


Answers (1)

best_answer

According to the conservation of momentum -

\mathrm{L_i=L_f }

\mathrm{m v R-I \omega=0 }

\mathrm{m vR=I \omega}..............(1)

put the given all values-

\mathrm{50 \times 1 \times 2=200 \times \omega }

\mathrm{\omega=1 / 2 }

Now,\mathrm{ (v+\omega R) t=2 \pi R }

\mathrm{ t\left(1+\frac{1}{2} \times 2\right)=2 \pi \times 2 }

\mathrm{ 2 t=2 \pi \times 2 }

\mathrm{ t=2 \pi \: \mathrm{sec} }

Hence option 3 is correct.








 

Posted by

Devendra Khairwa

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