# A metal coin of mass 5g and radius of 1 cm is fixed to a thin stick AB of negligible mass as shown in the figure . The system is initially at rest . the constant torque, that will make the system rotate about AB at 25 rotations per second in 5s, is closed to:Option 1)$4.0\times 10^{-6}Nm$    Option 2)$1.6\times 10^{-5}Nm$  Option 3)$7.9\times 10^{-6}Nm$Option 4)$2.0\times 10^{-5}Nm$

$\alpha =\frac{\Delta \omega }{\Delta t}=\frac{25\times 2\pi }{5}=10\pi\, \, \, rad/s^{2}$

$=\left ( \frac{5}{4}MR^{2} \right )\alpha$

$=\frac{5}{4}\times 5\times 10^{-3}\times \left ( 10^{-2} \right )^{2}\times 10$

$\simeq 2\times 10^{-5}Nm$

Option 1)

$4.0\times 10^{-6}Nm$

Option 2)

$1.6\times 10^{-5}Nm$

Option 3)

$7.9\times 10^{-6}Nm$

Option 4)

$2.0\times 10^{-5}Nm$

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