Calculate Static Equilibrium: SOH/CAH/TOA?

[Mason98]

Homework Statement

Sin for Y axis and Cos for X axis?

Relevant Equations

Sin = opp/hyp Cos = Adj / hyp

When calculating static equilibrium, i know that you have to split for example, F1 into F1x and F1y. when using soh/cah/toa is it always SIN for the Y axis and always Cos for the X axis? I've been following this method and getting it wrong some times it's really stressing me out, Thanks for any help in advance.

 

[Doc Al]

when using soh/cah/toa is it always SIN for the Y axis and always Cos for the X axis?

No. It all depends on what angle you are using. If the angle is with respect to the x-axis, then fine: The x-component would use cosine, etc. But if the given angle is with respect to the y-axis, things are reversed.

Remember that sinθ = cos (90° - θ).

 

[Mason98]

so that is how in the picture Fax is sin because the angle given is in respect to the y-axis which would mean to use sin?

 

[Doc Al]

so that is how in the picture Fax is sin because the angle given is in respect to the y-axis which would mean to use sin?

Exactly!

 

[Mason98]

Exactly!

Thank you very much! I appreciate your help :)

 

[NascentOxygen]

But if you adopt this as a new rule-of-thumb, you'll still be in a pickle when the problem gives you an angle which is relative to neither the x nor y axis.