Statics. A follower is held against a circular cam by a stretched spring. Determine force on roller.?

Question

A follower ABCD is held against a circular cam by a stretched spring which exerts a force of 6 lb for the position shown. Knowing that the tension in rod BE is 4 lb, determine
(a) the force exerted on the roller at A
(b) the reaction at bearing C

Diagram:
http://i231.photobucket.com/albums/ee84/janise87/16.jpg

Answer 1

The force at A is found by summing moments around C.
the spring force at B is 6x1.6, and is opposed by the tension of BE, 4x0.8, and the roller force at A. It's easiest to leave the force of A as X and calc the moment arm as the right triangle of CA (1.6) and the angle off of verticle, 30deg. so the moment arm is found from sin30=opp/hyp=radius / 1.6.
so you have 1 CW force and 2 CCW forces to set equal with only one variable.
then the reaction force at C is just the opposition to the sum of horizontal and veritcal forces, or graph by vectors if you prefer.