# Help with finding support reactions of a truss  Can you please help me find the answer to the above question, I am unsure how to work with F2 as I can't find the distance from Moment A or Moment J to this. Thank you

Whenever confused start from the basics: \begin{align} \sum M &=0 \\ \sum F_x &=0 \\ \sum F_y &=0 \end{align}

Therefore $$F_{a_y} = F_1 + F_2 \cos30= 1.5 + 2.598 = 4.09\text{ kN (up)}$$

J has no vertical reaction.

As for the moment sum we have: $$\sum M =0 \therefore F_{j,x}\cdot4 - (1.5\cdot2 + 2.598\cdot6 -3\cdot1/2\cdot2) =0$$

The last part in the parenthesis is the horizontal component of $$F_2$$ multiplied by its moment arm to get its contributory moment about A.

From here you can calculate horizontal reaction of J and then the horizontal reaction of A.

• Oh this makes sense, thank you!!
– Lila
May 8, 2019 at 14:24
• I'd just make it explicitly clear that the $1/2$ in the moment sum is actually $\sin(30)$.
– Wasabi
May 11, 2019 at 15:18

Welcome to Engineering! Have you considered that the force $$F2$$ has a component in the $$x$$ and the $$y$$ direction? If you break $$F2$$ down this way, you can observe that you now have a perpendicular distance to each of these components that you can use so sum the moments about one of the hinges.

If you sum the moments about the hinge $$A$$ you should only have one variable which is the horizontal support reaction at $$J$$.

You can then take that reaction into the sum of the forces to maintain equilibrium.

This is a conceptual guide to solving your problem, if you have any more specific issues I think it would be appropriate for you to show your work, and your issue here.