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

Answers (1)

\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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