Engineering Statics


A 2200 lb. tractor is used to lift 800 lb. of gravel. Determine the reaction at each of the two rear wheel and at each of the front wheels.

In the free body diagram the gravel load and weight of the tractor are shown.  In addition the forces at A and B are the sum of the two rear 
tires at A and the two front tires at B.
Taking moments about point A, allows the equation only to have one 
unknown in it, the force at B.  (Note that the force at A passes 
through point A and hence since there no distance from A to the 
force, there can be no moment.)
The force at B is divided by two to get the force on each front tire.
The summation of forces in the y direction allows us to solve for the 
force at A, since the force at B is already known.  (Alternately, we 
could also have taken the sum of moments about point B and solved for 
the force at A.)
The force at A is divided by two to get the force on each rear tire.