Posted by lala on .
Suppose a crate of mass 2.8 kg is placed on the plank in the figure below at a distance 5.1 m from the left end. Find the forces exerted by the two supports on the plank. (The mass of the plank is 12.0 kg.)
Left Support N
Right Support N
The plank set on two pivots one at 3.0m from the left, and the other 2.0m from the right. There is 7.0m between the two pivots

Physics 
drwls,
The sum of the two forces is
F1 + F2 = (2.8 + 12.0) g Newtons
To get F1 or F2, set the sum of the moments about either support equal to zero. The weight of the plank acts at its center of mass.
You should be able to write that equation by looking at the figure you have not provided.