Cosine, Sin, Tangent when find force/tension

[lokobreed]

Ok... so I had this down and now I am all confused ;/

I am not posting in the homework sections because its not for homework although I will gie an example of a problem... I just want to understand why/how they use these to find the force/tension...

Example:
A 20 kg loudspeaker is suspended 2m below the celing by two cables that are each 30* from vertical. What is the tension in the cables?
For this I will cable 1 T1 and cable 2 T2.

So to find the X compenent of forces
since the x would use the 30 degree angle and it would be using the hyp and adjacent sides I will use the cos of the angle to find them
-T1x + T2x = 0 N --> -T1 COS 30 + T2 Cos 30 = 0

Now where I am confused is how to find the Y compent and why you would do it the way you do... I know you use sin but I just don't understand how you can use the opposite angle if it is not known... perhaps I am missing something ... please help!

 

[S_Happens]

You don't use a different angle. You use sine of the same angle, which instead of adjacent over hypotenuse as it was for cosine, is opposite over hypotenuse.

There is no "x uses the 30 degree angle" and y uses the opposite angle. Sine and Cosine can relate the angle and two sides of a triangle. With three variables, you need to know two to solve for the third.

Also, in this case if one angle given is 30, then you do indeed know all the other angles of the triangle. This is all done by right triangles, which means one angle has to be 90.

 

[lokobreed]

Thank you! What you said just made me remember everything somehow!
Thank you!

 

[S_Happens]

Everybody gets one.

J/k. Glad I could help.