# A Little Physics Problem

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#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
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16 years ago
#2
If onllllly I could be arsed
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#3
Maybe it is the wrong time of the year to be asking people to look at physics problems
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16 years ago
#4
what is W?
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16 years ago
#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
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#6
(Original post by elpaw)
what is W?
Sorry it is just a fixed constant. The answer should be in terms of W.
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16 years ago
#7
(Original post by elpaw)
what is W?
Why didn't you reply to my PM?
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16 years ago
#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
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#9
The wires are extensible.
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16 years ago
#10
(Original post by shiny)
The wires are extensible.
aaah, that compolicates the situation slightly....
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16 years ago
#11
does the load force act vertically downwards or perpendicular to the bar?
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#12
(Original post by elpaw)
does the load force act vertically downwards or perpendicular to the bar?
Straight down
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16 years ago
#13
Shiny, wanna just right the whole question out, PROPERLY - with all the info, this time though?
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16 years ago
#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
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16 years ago
#15
I meant write as well
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16 years ago
#16
are the wires light too?
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16 years ago
#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...
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#18
Yes, the wire is light.
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#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!
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16 years ago
#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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