Answer:
When you lift only one end of the 5 m uniform rod you are effectively raising its center of mass located at its geometric center. The center of mass of this uniform rod is at the 2.5 m point. So instead of using the full weight of 10 N weight the needed force is only one-half of the weight which is 5 newtons.
The work done by lifting the full rod to a height of h is
weight * h = 10 N * h but in this condition h is only 1/2 * h so the work done is one-half of the work. 1/2 * weight * h = 1/2 * 10 N * h
Work done = 5 N * h which makes the force needed equal to 5 newtons
