Calculating tension in each of 3 strings

1. Oct 10, 2008

mathsgeek

I have got a question i am having a lot of trouble with. The question is that three strings on unequal lengths are used to support a mass of 50g. All of these strings are used to support the weight. Two of these strings cannot be in the same plane as the other string. Determine the tension in each String.

Well, i have 2 strings in the i and j plane and was thinking to have a third string in the k or k and j plane. However i do not know if this is correct. Also, could someone show me the general steps on how to calculate the tension in each string as i am having trouble with calculating this.

2. Oct 10, 2008

Rake-MC

It's going to depend exactly on how you define your planes and the angles that follow.

3. Oct 10, 2008

mathsgeek

well the planes are goin to be defined in terms of i, j and k.

4. Oct 10, 2008

Rake-MC

So you're putting the j plane parallel to the acceleration due to gravity?
There are potentially infinite solutions to this question, I must be interpreting it incorrectly. Is that the exact wording of the question? Could you not have 1 string hanging from a ceiling straight down parallel to gravity, then two strings of equal tensions opposing each other perpendicular to the acceleration due to gravity?

5. Oct 10, 2008

mathsgeek

The strings have to be of unequal length though. And yes the j component is the same as y. (vertical)

6. Oct 10, 2008

Rake-MC

It gives no definition of where they have to be fixed though? The end that is not fixed to the mass I mean.

7. Oct 10, 2008

mathsgeek

its basically fixed to a wall or sumthing, so it must be fixed at both ends.

8. Oct 11, 2008

mathsgeek

any1? Its urgent. Thanks

9. Oct 11, 2008

Redbelly98

Staff Emeritus
Draw a freebody diagram.

Fnet = 0 for x, y, and z directions.

It depends on what angles the strings are oriented, which you know (hopefully) but we don't know.

10. Oct 11, 2008

mathsgeek

Heres a pic of 2 of the strings:

i just cant think of the length to place the third one in the k (or k and j) plane. Could u guys make sum suggestions and show me the process and calculations with ur sugeested length as i am having trouble calculating it. Thanks

11. Oct 12, 2008

Redbelly98

Staff Emeritus
Yes, placing the 3rd string in the k-j plane would make sense. Are you free to choose the string lengths and angles? Making the arrangement as symmetric as possible is probably the best way to approach this, so perhaps making all 3 string lengths equal.