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M1, easy Tension question leaves me stumped watch

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1. I don't know why I can't get my head around this one

A string of weight W newtons is attached at C to the ends of two light inextensible strings AC and BC. The other ends of the strings are atached to the 2 fixed points A and B on a horizontal ceiling. The particle hangs in equil with AC and BC inclined to the horizontal at 30 and 60 degrees respectivelyl. Given that the tension in AC is 50N

a) calculate the tension in BC, does the tension act only upwards in the string towards the ceiling, or does it go both ways like when a particle is suspended from a pulley?

b) the value of W

thx
2. (Original post by ramroff)
I don't know why I can't get my head around this one

A string of weight W newtons is attached at C to the ends of two light inextensible strings AC and BC. The other ends of the strings are atached to the 2 fixed points A and B on a horizontal ceiling. The particle hangs in equil with AC and BC inclined to the horizontal at 30 and 60 degrees respectivelyl. Given that the tension in AC is 50N

a) calculate the tension in BC, does the tension act only upwards in the string towards the ceiling, or does it go both ways like when a particle is suspended from a pulley?

b) the value of W

thx
Force left = force right
horizontal component of AC = horizontal component of BC
50cos30 = BCcos60
25√3 = ½BC
BC = 50√3 N

force up = force down
weight of string = sum of vertical components of AC and BC
W = 50sin30 + 50√3sin60
W = 25 + 75
=100N

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Updated: June 6, 2005
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