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I have two rods with lengths $L_1$ and $L_2$, connected with a joint in the middle and I would like to express the moment(torque) around a point mass (P) at the far end of rod 1. The relation between the rods is expressed by the angle $\gamma$. Two forces act upon the far end of rod 2, $F_A$ and $F_B$, the latter orthogonal to the rod and the former along the rod in the heading of the joint. For the force $F_A$ the moment should be $F_A * L_1 * \sin{\gamma}$. What I'm not sure of is how the force $F_B$ should act, will it be a torque in the joint that can be translated to the point mass, i.e. $- F_B * L_2 $ or will it not affect the point P?

Thank youImage describing the problem

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Draw a line from P to the tail of F(b). Now, the length of that line multiplied by the component of F(b) perpendicular to that line gives the torque due to F(b) about P. Nothing more.

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See, by definition torque is the product of force and the perpendicular distance between the line of action of the force and the axis from where the torque is being measured . By your figure it is $F_B ×(L_2+L_1cos \gamma)$

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