# Homework Help: Tension question

1. Oct 10, 2007

### anglum

since there is a picture for this problem i am providing a link to view the problem

http://i199.photobucket.com/albums/aa314/anglum/help2.jpg

i solved for tension of T1 by taking the sin55=90/T1
solved for T1 and converted to kg and got 11.211 kg which was incorrect

since the remainder of the problems are dependent on having T1 right i am now stuck

not sure what to do since the forces on the "knots" is equal to zero i used pythagorean theorem to get my answer since i knew the vertical force on T1 was 90N

thank you

2. Oct 10, 2007

### anglum

i have to start solving all of the problems contained by first gettin T1 value correct?

3. Oct 10, 2007

### PhanthomJay

what about the T2 force at this knot? You've got to use Newton 1 in both the x and y directions to solve for the 2 unknown forces with the 2 equations.
why are you converting a force to a mass unit?

redo the T1 calc

4. Oct 10, 2007

### anglum

i am converting the force to Kg cuz part 1 of the problem asks for tension in T1 in units of kg

i drew a vertical line down from teh top to the knot ... then knew the force of that had to be 90 N... thus sin55 = 90/T1 correctt???

5. Oct 10, 2007

### anglum

if i solve for T1 that way i get 109.8678N and that is incorrect

6. Oct 10, 2007

### PhanthomJay

No. You must isolate the knot and note that there is both a T1sin 55 and a T2sin 10 componnent in the vertical direction, one acting up and the other down, the sum total of which algebraically adds to 90 newtons. Look in the x direction as well and apply newton 1 again. You get 2 equations with 2 unknowns, which you can now solve for T1 and T2. I don't know why you would convert the tension to kilos, must be a misprint.

7. Oct 10, 2007

### anglum

so my equation to solve looks like this

T1sin55 + T2sin10 = 90N ?????

8. Oct 10, 2007

### PhanthomJay

Watch your signs. T1 component acts up, T2 component acts down.

9. Oct 10, 2007

### anglum

ok so itd be T1sin55 - T2sin10 = 90N???? and that is just the vertical tension on that one

and the horizontal would be T1cos55 - T2cos10 = 0????

10. Oct 10, 2007

### PhanthomJay

Yes, good, solve for T1 and T2, then move to the next knot.

11. Oct 10, 2007

### anglum

how am i supposed to solve for T1 and T2 ??? combine those equations???

12. Oct 10, 2007

### learningphysics

Yes, the equations are right. Solve for T2 in one equation and plug it into the other equation.

13. Oct 10, 2007

### anglum

if i solve for T2 in the 2nd equation i get -T2 = -T1cos55/cos10

14. Oct 10, 2007

### learningphysics

yup, so T2 = T1cos55/cos10, you can plug in cos55 and cos10...

15. Oct 10, 2007

### anglum

ok so then i get where T1 = X

.81915X - .57357X/.98480 = 90 ?????

16. Oct 10, 2007

### learningphysics

you forgot to multiply by sin10

17. Oct 10, 2007

### anglum

o sooo

.8195X - .57357X/.98480 (.173648) = 90??????

18. Oct 10, 2007

### learningphysics

looks right.

19. Oct 10, 2007

### anglum

so i then get .8159X -.57357x/.98480 = 90/.173648

then i get

.8159X - .57357X = (90/.173648) * (.98480)

.24233X = 510.4118677

T1 = 2106.267766 that cant be right??!?!

20. Oct 10, 2007

### anglum

my math has to be wayyyy off