Four equal masses M are placed at equal intervals, l, along a horizontal straight rod whose mass can be ignored. The system is to be rotated about a vertical axis passing through the mass at the left end of the rod and perpendicular to it.
A) what is the moment of inertia of the system about this axis?
B) What minimum force, applied to the farthest mass, will impart an angular acceleration α?
C) what is the direction of this force?