The railway crossing gate consists of the 100-kg gate arm having a center of mass at G_a and the 250-kg counterweight having a center of mass at G_W. Determine the magnitude and directional sense of the resultant moment produced by the weights about point A.
Let us write a moment equation around point A. We will assume clockwise movement to be positive.
(Notice how we got a negative answer. It simply means the moment being produced is in a counterclockwise direction)