I can\'t seem to get the Custom Diagram to work so here is a link tomy problem:

Question

I can't seem to get the Custom Diagram to work so here is a link tomy problem:

http://books.google.com/books?id=nYRMrMu9hJAC&pg=PA101&lpg=PA101&dq=%22The+20-kg+mass+is+suspended+from+the+three+cables.+Cable+AC+is+equipped+with+a+turnbuckle&source=bl&ots=8-NA4zPjSZ&sig=TXsFUnE9fHEBHFReXcMpN8OVxxU&hl=en&ei=lw9uS8f1OoTCsgOMqcmxDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAkQ6AEwAA#v=onepage&q=&f=false

Its Question 3.33.

I first found the unit vectors and then multiplied it with theirrespected magnitudes to get two equations:

Fx=0
=> TAB (-.53) + 40(.53)+TAD (.809)=0
and
Fy=0
=> TAB (.848) + 40(.848) + TAD (.588) -W=0

But I keep getting a negative answer of TAD . So Iassume I'm doing something wrong

Any tips?

Explanation / Answer

Your equations are right. W=20*9.81 = 196.2 [N]
From the first equation: Tad = (1/0.809) * (0.53 * Tab - 21.20) = 0.655 Tab -26.21
Substitute this in the second equation: 0.848 * Tab + 33.92 + 0.588 * (0.655 Tab - 26.21) - 196.2=0 1.23 * Tab - 177.70 =0 Tab = 177.70/1.23 = 144.1 [N]
Substitue this in the equation for Tad:
Tad =  0.655 Tab - 26.21 = 0.655 * 144.1 -26.21 = 68.2 [N]

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