What is the Beam Support Force Question?

[enveng2013]

Homework Statement

Ok so I have a beam with the forces shown below. There is a 3 m span between the supports (A&B) and both of the supports are 1.5 m from the end of the beam. The 60 lb force is .75 meters left of support A and .75 m from the left end of the beam. P is an unknown force which I must solve for at the right end of the beam. I am allowed 33.75 lb on the left support and 93.75 lb on the right (this came from a stress equation I'm pretty confident those numbers are right).

Homework Equations

No real relevant equations except moment and force.

The Attempt at a Solution

So the force at A should be described by the moment around B divided by the distance from B to A. Thus giving a beam where the moment forces are zero.

FA=(P*1.5-60*3.75)/3

Then force B can be related to A because the forces in the y direction must be zero or the beam would move

Thus FB=(60+P)-FA or FB=(60+P)-(P*1.5-60*3.75)/3

I've tried plugging in the maximum forces for both but I can't seem to get an answer that works for both supports.

If you guys could help me or even steer me in the right direction that would be great.

 

[SteamKing]

You've got to write all of the equations of equilibrium in order to obtain correct solutions for RA and RB. That means the sum of the forces = 0 and the sum of the moments = 0.
As the problem is stated, you have three unknowns (P, RA, and RB) and have shown only one moment equation (sort of).

 

[enveng2013]

I actually just looked at a solutions manual. I got the answer right from what I had. It just didn't seem right to me for some reason.

 

[SteamKing]

If only Life came with a solutions manual.

 

[enveng2013]

They're not always useful. Sometimes though, it's nice to know what you got was right.