Answer
The force on the deltoid muscle is about 1600N
Work Step by Step
We sum the torques about the shoulder joint to find the force on the deltoid muscle. Therefore;
$(+ \circlearrowleft) \sum \tau=0$
$F_M*\sin15^{\circ}*.12m-mg*.24m-8.5kg*g*.52m=0$
$F_M=\frac{mg*.24m+8.5kg*g*.52m}{\sin15^{\circ}*.12m}$
$F_M=\frac{3.3kg*9.8m/s^2*.24m+8.5kg*9.8m/s^2*.52m}{\sin15^{\circ}*.12m}$
$F_M\approx1600N$
The force on the deltoid muscle is about 1600N.