Bob B of mass m at rest is hanging vertically from the ceiling via a massless string of length 10 m, as shown in the figure. Point mass A of mass m…

Bob $\displaystyle B$ of mass $\displaystyle m$ at rest is hanging vertically from the ceiling via a massless string of length $\displaystyle 10$ m, as shown in the figure. Point mass $\displaystyle A$ of mass $\displaystyle m$ travelling horizontally with speed $\displaystyle 10 \mathrm{~ms}^{-1}$ hits bob $\displaystyle B$ elastically. The bob $\displaystyle B$ rises $\displaystyle h$ meter after the collision. Taking the acceleration due to gravity $\displaystyle \mathrm{g}=10 \mathrm{~ms}^{-2}$ and neglecting the size of the bob, the value of $\displaystyle h$ is :