[单选题]
Disc A rotates around a vertical fricti;pwxca y)q6j+2.rapq onle/2*lt(zhw:7ei5+w d rcvo kzo mc*eo;2st 6d mss axle with angular speed $ω_A$ and moment of inertia $I_A$. Disc B with moment of inertia $I_B$ is dropped from rest on disc A. The ratio$\frac{I_B}{I_A}$=$\frac{1}{4}$
The two discs have the same final angular speed ω.
What is the ratio $\frac{(Final\,kinetic\,energy)}{(Initial\,kinetic\,energy)}$ ?
A. $\frac{1}{4}$
B. $\frac{1}{2}$
C. $\frac{4}{5}$
D. $\frac{5}{4}$
