# Find the values of F1 and F2

• Aug 19th 2009, 09:52 AM
SmallMan
Find the values of F1 and F2
The diagram shows three cables tied to a small metal ring. F1, F2 and F3 are the forces applied to each cable.

http://img6.imageshack.us/img6/2456/41089266.jpg

a) Write down the x and y components of each vector.
b) Hence determine the values od F1 and F2

I spent a few hours for this and i can`t manage :( can somebody tell me how to solve this ?
• Aug 19th 2009, 10:06 AM
bandedkrait
Er the question seems pretty straightforward.

The ring in question is in equilibrium. So the resultant of all the forces on it has to be zero.

So the components of F1, F2, F3 in X-Direction Y-Direction should add in such a way as to result in zero.

The component of the forces in X direction is merely the magnitude multiplied by the cosine of the angle made by the forces with POSITIVE X-axis.

So,
component of F1 = F1cos(30) = sqrt(3)F1/2
Component of F2= F2cos(90+45) =F2cos(135)= -F2/sqrt(2)
Component of F3 =F3cos(90+180)=F3cos(270)=0

Now, for equilibrium
F1cos30+F2cos45=0

Hence sqrt(3)F1/2 = F2/sqrt(2)........(1)

Similarly find the components of F1, F2,F3 along Y- direction.

It is the magnitude multiplied by the sine of the angle made by the force with the X-axis

Hence,
Components are F1sin(30), F2sin(135) and F3sin(270)
i.e. F1/2, F2/sqrt(2), -F3

Again, these components should add to give zero. Thus you obtain another equation in F1 and F2 as F3 is known.
Solving them simultaneously will yield F1 and F2.
• Aug 19th 2009, 10:46 AM
SmallMan
F1/2 + (F2sqrt)/2 + (-F3) must be 0 ?
• Aug 19th 2009, 10:48 AM
bandedkrait
Yes. for equilibrium of the ring.
• Aug 19th 2009, 11:20 AM
SmallMan
Thank YOU bandedkrait - you really helped me. I`m your debtor :)