A circular disc of mass M and radius R is rotating about its axis with angular speed ω_1. If another stationary disc having radius R/2 and same mass…

A circular disc of mass M and radius R is rotating about its axis with angular speed $\displaystyle \omega_1$. If another stationary disc having radius $\displaystyle \frac{R}{2}$ and same mass $\displaystyle M$ is dropped co-axially on to the rotating disc. Gradually both discs attain constant angular speed $\displaystyle \omega_2$. The energy lost in the process is p% of the initial energy. Value of p is \_\_\_\_.