Arm problem, Static Equilibrium

[Bones]

Homework Statement

(a) Calculate the magnitude of the force, FM, required of the "deltoid" muscle to hold up the outstretched arm shown in the figure. The total mass of the arm is 3.3 kg.

(b) Calculate the magnitude of the force FJ exerted by the shoulder joint on the upper arm
http://www.webassign.net/gianpse4/12-56.gif

Homework Equations

The Attempt at a Solution

I got part a:
tnet=mg(24m)-Fmsin15(0.12m)=0
Fmsin15(0.12m)=(3.3kg)(9.8m/s^2)(0.24m)
Fm=(3.3kg)(9.8m/s^2)(0.24m)/0.03106m
Fm=250N

How do I figure out Fj for part b?

 

[LowlyPion]

Consider the effect of the cosine component of the deltoid force back into the joint.