There is a semispherical smooth pit of radius $R$ in a horizontal plate. A small ball of mass $m$ is attached to its edge in point $A$ by a thread of length $L$. Initialy, the thread is taut and the ball is in contact with the edge (see figure).
The ball is released and begins to slide down with zero initial speed.
Determine the tension in the thread at the moment the ball reaches the lowest point.
