Question $2$:

Two identical $20-$kg spheres are attached to the light rigid rod, which rotates in the horizontal plane centered at pin $O.$ If the spheres are subjected to tangential forces of $P=20N,$ and the rod is subjected to a couple moment $M=(8t)N-m,$ where t is in seconds, determine the speed of the spheres at the instant $t=4s.$ The system starts from rest. Neglect the size of the spheres.

Figure for Question $2$