# Swirling Disc in Chocolate!

Find the External Torque that has to be supplied to a disc rotating about an axis perpendicular to it and passing through its center of mass to maintain it at the same angular velocity, placed on top of a layer of viscous liquid of coefficient of viscosity $$\eta$$ of height $$h$$. Give your answer to 2 decimal places.

It is a thin disc. The brown liquid is the viscous liquid.

Details and Assumptions:

• Mass of Disc : $$M = 1 \text{ kg}$$

• Radius of Disc : $$r = 2 \text{ m}$$

• Height of Liquid layer : $$h = 0.15 \text{ m}$$

• Coefficient of Viscosity : $$\eta = 20 \text{ S.I Units}$$

• Initial angular velocity : $$\omega = \frac {10}{\pi} \text{ rad/s}$$