# Oscillating disk under action of point source of light.

Consider a disk of radius $$R$$ and mass $$m$$, which is hanging in air due to the balancing of its weight by the force on it due to a point source of light having power $$P$$ kept on its axis at a distance $$h$$ from its center as shown:

Now, the disk is translated up through a small distance and released. Derive an expression for the time period of its oscillations in terms of $$h$$ and $$R$$. Find the value of the time period in $$\text{seconds}$$ for $$h = 2$$ meters , $$R = 1$$ meters. Take the value of $$g$$ as $$9.8 m/s^2$$

Assume that the disk is perfectly reflecting.

×