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# A Little Physics Problem watch

1. A light bar is held in suspension by three identical wires (see attachment). A point load of force 4W is applied to the bar at the position indicated. Find the forces in the wires
Attached Images

2. If onllllly I could be arsed
3. Maybe it is the wrong time of the year to be asking people to look at physics problems
4. what is W?
5. Assuming 4W is 4 times an unknown W, calling the three tensions from left to right a, b and c:

Resolving vertically,

4W = a + b + c

Taking moments from A:

4LW = 2Lb + 4Lc

Taking moments from B:

4LW + 2Lc = 2La

Taking moments from C:

12LW = 2Lb + 4La

Simplifying:

4W = a + b + c
2W = b + 2c
2W = a - c
6W = b + 2a

These won't solve though... grr
6. (Original post by elpaw)
what is W?
Sorry it is just a fixed constant. The answer should be in terms of W.
7. (Original post by elpaw)
what is W?
Why didn't you reply to my PM?
8. its not impossible, but there isnt a single answer

if the tensions in the strings from left to right are x,y and z respectively, you can have any number of tensions which satisfy:

x = 2 + z
y = 2 - 2z
9. The wires are extensible.
10. (Original post by shiny)
The wires are extensible.
aaah, that compolicates the situation slightly....
11. does the load force act vertically downwards or perpendicular to the bar?
12. (Original post by elpaw)
does the load force act vertically downwards or perpendicular to the bar?
Straight down
13. Shiny, wanna just right the whole question out, PROPERLY - with all the info, this time though?
14. (Original post by thenarbisbanned)
Shiny, wanna just right the whole question out, PROPERLY - with all the info, this time though?
the question was worded poorly with not enough info anyhow this won't come up in a physics exam
15. I meant write as well
16. are the wires light too?
17. Extensible rods, which Mechanics book is that featured in? I am only a beginner... but id like to know where I have the pleasure of learning that...
18. Yes, the wire is light.
19. (Original post by CasedIt)
the question was worded poorly with not enough info anyhow this won't come up in a physics exam
Most questions in life won't come up in a physics exam. It doesn't mean you don't have a go at it!
20. (Original post by RobbieC)
Extensible rods, which Mechanics book is that featured in? I am only a beginner... but id like to know where I have the pleasure of learning that...
the rod is also extensible now?

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