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Most Important Selected Qs for JEE AdvancedPhysicsRotational Motion

A cylinder as shown in the figure is filled with oil of viscosity . Within the cylinder, a thin disc of radius R is rotating with a constant angular velocity about its symmetrical, vertial axis. The separation between the disc and the horizontal plane of the cylinder is y . Viscous forces act on the disc. Chose the correct option(s). Due to viscous forces on the disc

Options

  1. Athe value of total torque is = R^4 y
  2. Bthe value of power developed is = ^2 R^4 y
  3. Ctotal value of torque is = ^2 R^4 2 y
  4. Dthe value of power developed is = ^2 R^4 y

Correct answer

B. the value of power developed is = ^2 R^4 y

Step-by-step solution

Consider an element of radius r and thickness dr Viscous force acting on it is given by d F=2 ( 2 r d r r y )[ Viscous force acts from both top and bottom contact layer of the dise) aligned & d = torque =r d F=4 y r^3 d r & Total torque = 4 y ₀^R r^3 d r & = R^4 y Power developed = = ^2 R^4 y aligned

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