A wagon of mass `M` can move without friction along horizontal rails. A simple pendulum consisting of a sphere of mass `m` is suspended from the ceiling of the wagon by a string of length l. At the initial moment the wagon and the pendulum are at rest and the string is deflected through an angle `alpha` from the vertical. Find the velocity of the wagon when the pendulum passes through its mean position.

Answer

`"["2m sin (alpha//2)sqrt((gl)/((M+m)M))"]"`