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GLewellen
29th October 2002, 23:29
ok here is the problem:

(let n^o = number degrees)

Joe wishes to hang a sign weiging 750 N so that cable A attached to the store makes a 30^o angle. Cable B is horizontal and attached to an adjoing building. What is the tension in cable B?

figure:

30^o |
|\ |
| \ |
| \ A |
| \ |
|_x__\[____B_____]
| | | |
| |____| |
| 750 N |

i've been thinking this over, and for some reason my results don't come out reasonable.

what i've been doing:
sin(x) = o / h
sin(30) = x / A
A = x/sin(30)

sin(x) = o / h
sin(0) = 0/B
B = 0/sin(0)
B = Undefined

i know that there are some smart folk in this forum, help.

Orgone_Man
30th October 2002, 00:08
hmm.... try force vector summations about a point in the x AND y directions. They must all equal zero due to the fact that the system is in an ideal stasis (not moving) and there is no accelleration. (F=ma the bread and butter of my college education).

F =ma
x x

F =ma
y y

F =F =0
x y

It seems that the forces are as follows:

750N in -y direction

TB (tension in rope B, don't attach a neg or pos sign here yet, it will be discovered by using the multiple equations and solving for it, I'm sure you know this but I don't know if you are in highschool or what)

Ax

Ay

Ax + TB = 0
Ay + (-750) = 0

here we are left with 2 equations and 3 unknowns, so we need to turn Ax and Ay into one variable by doing this:

sin(30)=Ax/A
cos(30)=Ay/A

solve for Ay and Ax in terms of A and throw it into the 2 equations to get your answer. I guess this will work, haven't touched the stuff in 2 years.

hgnis
30th October 2002, 00:15
Originally posted by GLewellen
ok here is the problem:

(let n^o = number degrees)

Joe wishes to hang a sign weiging 750 N so that cable A attached to the store makes a 30^o angle. Cable B is horizontal and attached to an adjoing building. What is the tension in cable B?

figure:

30^o |
|\ |
| \ |
| \ A |
| \ |
|_x__\[____B_____]
| | | |
| |____| |
| 750 N |

i've been thinking this over, and for some reason my results don't come out reasonable.

what i've been doing:
sin(x) = o / h
sin(30) = x / A
A = x/sin(30)

sin(x) = o / h
sin(0) = 0/B
B = 0/sin(0)
B = Undefined

i know that there are some smart folk in this forum, help.

Yawn....
B = A sin 30
A cos 30 = 750
Thus, B = 750 tan 30
Yawn...
PS...if you are a hot chick....shit this is Form 1 physics...never mind

:weird: ;)

Orgone_Man
30th October 2002, 00:28
hmm... guess I went a little overboard. Once you take higher level courses like machine design or whatever, the simple problems of physics and statics seem to be way more convoluted than they need to be.

rm'
30th October 2002, 00:46
And we all know that the simplest solution to a physics problem is to switch over to the Humanities :-p

Orgone_Man
30th October 2002, 00:49
Originally posted by rm'
And we all know that the simplest solution to a physics problem is to switch over to the Humanities :-p

sadly, the longer I intern as a mechanical engineer, the more I want to become a writer.

hgnis
30th October 2002, 00:55
Originally posted by Orgone_Man

sadly, the longer I intern as a mechanical engineer, the more I want to become a writer.

And the longer I spend as a Mech E....:(
Damn, where did the chicks go?
I guess that's why rm is doing Humanities...:eek:

Widdykats
30th October 2002, 01:20
Originally posted by hgnis

And the longer I spend as a Mech E....:(
Damn, where did the chicks go?
I guess that's why rm is doing Humanities...:eek:

"Fine"

smeggle
30th October 2002, 01:28
I remember when I did engineering at college and we had to do all that kind of stuff.Cause first job comes along and I'm being really clever working all this stuff out when all I needed was force of gravity and weight of object, equals tension on line and the boss turns round and says just get a cable bloody strong enough to hold it and stop pissing about. years of college and all I got from him was this .DOGH!
No wonder I switched to humanities + the birds were better looking!!!( true though ain't it Rm snicker snicker):D :D :D

FreeParty Posse The True sound of DANCE

hgnis
30th October 2002, 01:51
Originally posted by Widdykats
"Fine"

What's the matter now?
Ok! I'll shut up....
At least you didn't sigh loudly.
:p

rm'
30th October 2002, 03:32
Originally posted by smeggle
( true though ain't it Rm snicker snicker):D :D :D

The poor suckers don't know what they are missing :blah:

Avalon
30th October 2002, 03:36
Originally posted by rm'

The poor suckers don't know what they are missing :blah:

Is lost here....