Question

A Christmas ball in a shape of a hollow sphere ia hung from the tree by a piece of a thread attached to the surface of the ball. The mass and radius of the ball are 0.105kg and 0.12m, respectively. What will be its period of oscillation when slightly displaced from its equilibrium position?

Hint: l= 5/3mr²

Answer 1

$$T=2\pi\sqrt\dfrac{I}{mgL}=2\pi\sqrt\dfrac{5mr^2}{3mgr}=2\pi\sqrt\dfrac{5r}{3g},\\\space\\ T=0.9\text{ s}.$$