Engineering Mechanics, vector components parallel to 2 bars

In the example we took in lecture and in the book the force that we were asked to find the components for was in the between the 2 lines, but in this question it isn't. I managed to get one of the components correct after 1 hour of trying to solve this but I have no idea how that answer came about lol, HELP !!
Question 2.8

Anyone?

The component of a force in a given direction is the product of; the magnitude of the force and the cosine of the angle between the force and the given direction, so in this case:

80k cos 110, and 80k cos 150.

Im afraid this method doesnt work,, because the components dont necessary make a right angle with the force so you need to use another trigonometry method for this,,

Should work. What are the given answer?

Fab= 117.0 KN Fac= 62.2 you want to take a look at the given example?

I think it would help. I suspect you're not resolving the force, but rather trying to write the force as the sum of two other forces in the directions AB and AC.

And here's an alternative diagram, more along the lines of your example. You extend AB and AC, to give:

The reason for extending AB, AC, is that the component of F in the directions AB,AC could be negative, and indeed one of them is (AB).

Am a little confused, in the diagram AB and AC are both directed to the opposite side of F , why is one of them negative?

The sum of the forces acting in AB, AC, and the force F, must be zero, and since both AB, AC are to the left of F, one of them must apply a negative force. I.e. one spar is under tension (AB), and one is under compression (AC).

Make sense?

Hmm,, why is AB the negative force then?

Because you're considering resolving F into components, rather than looking at the reaction in the spars, which will be the negative of the F components.


Watching a film at present, so response may take a while.

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