Hanged bird feeder

The above diagram shows a bird feeder hanging from the ceiling by three wires A , B A, B and C . C. Wires A A and B B form angles of 6 0 60^{\circ} and 3 0 , 30^{\circ}, respectively, with the ceiling. Wire C C is hanging from the intersection of A A and B , B, and is connected to the top of the bird feeder. If the weight of the feeder is 65 N , 65 \text{ N} , what is the tension force on the wire B ? B?

45.0 N 45.0 \text{ N} 65.0 N 65.0 \text{ N} 20.0 N 20.0 \text{ N} 32.5 N 32.5 \text{ N}

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2 solutions

Chew-Seong Cheong
Jul 26, 2014

Let T A T_A and T B T_B be the tensions in wire A A and B B respectively. Then equating the horizontal forces: T A c o s 6 0 = T B c o s 3 0 T_Acos60^\circ = T_Bcos30^\circ T A = 3 T B \Rightarrow T_A = \sqrt{3}T_B Now equating vertical forces, we have: T A s i n 6 0 + T B s i n 3 0 = 65 T_Asin60^\circ + T_Bsin30^\circ = 65 3 2 T A + 1 2 T B = 65 \Rightarrow \frac{\sqrt{3}}{2} T_A + \frac{1}{2}T_B = 65 3 2 T B + 1 2 T B = 65 \Rightarrow \frac{3}{2} T_B + \frac{1}{2}T_B = 65 2 T B = 65 T B = 32.5 N \Rightarrow 2 T_B = 65 \Rightarrow T_B=\boxed{32.5N}

Kevin Mano
Jul 16, 2014

Equating the forces vertically and horizontally, we have two equations that go like so: Let tension at A be called A and the tension at B be called B (for simplicity)

Asin60+Bsin30=65 (forces vertically)

Acos60=Bcos30 (forces horizontally)

Using the second equation: Acos60=Bcos30

A(0.5)=B(sqrt3/2)

Hence A=(sqrt3) B

Substituting that into the first equation, we get: (sqrt3)B(sqrt3/2)+(0.5)B=65

1.5B+0.5B=65

Hence 2B=65 and B=32.5N

I'm not familiar with all these math editor stuff yet, as this is my first solution post, but I hope everyone gets the solution. I've kept it as simple as possible. Hope everyone understands. Cheers!

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