Question

A fidget spinner of radius 0.05 m has a moment of inertia1.25×10^-4 kg m2

and 

is rotating at 8.4 rad s-1

. A large fly whose mass is 0.3 kg lands onto the edge of 

the rotating spinner. Calculate the angular speed of the system after the fly falling 

onto the spinner. 

Answer 1

Apply conservation of angular momentum:

$$I\omega=I_1\omega_1,\\\space\\ \omega_1=I\omega/I_1=\\=(1.25·10^{-4})(8.4)/(0.3·0.05^2+1.25·10^{-4})=\\=1.2\text{ rad/s}.$$