What Are the Forces in Equilibrium for a Weight Hanging on a Rod?

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In the discussion about a weight hanging on a rod, participants analyze the forces in equilibrium, focusing on the hinge force and the tension in the wire. A force diagram is created to illustrate the forces acting on the rod, including the weight (mg) and tension components. The conditions for equilibrium are established with equations for horizontal and vertical forces, as well as torque around the wall attachment point. The conversation highlights the importance of considering the vertical reaction force at the hinge, which should be treated as a separate component rather than part of the hinge force. The clarification emphasizes the need to accurately account for all forces to solve for the hinge and tension forces correctly.
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Homework Statement


A light rod is holding a weight with mass m in equilibrium. The rod is attached to the wall with a hinge and a wire as shown on the figure.

http://sveskekat.dk/files/uploads/phys_4.PNG

Problem:
Draw a force diagram of the rod and determine the force with which the hinge affects the rod and the tension force in the wire.

The Attempt at a Solution


I did the force diagram as shown on the figure, with the green arrows as the forces.
I want to determine
The force with which the hinge affects the rod, Fc.
The tension force in the wire, T.

I have that Ww = mg.

I wrote up the conditions for equilibrium,
\sum F_x = F_c - T cos(45) = 0
\sum F_y = T sin(45) - W_r - mg = 0

I do torque around the attachment point on the wall,
\sum \tau = 2amg + aW_r - aF_c = 0

But trying to solve for e.g. F_c now gives me
F_c = cos(45) \frac{F_c - mg}{sin(45)} = F_c - mg,
which is kinda bad. What am I doing wrong??
 
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Since it is given that the rod is light, you can ignore W_r. But you are forgetting the vertical reaction at O.
 
Hi Jay, thanks. I will ignore W_r then. How should the vertical reaction at O look like? Should it be another component, or should it be part of F_c?

Thanks.
 
Call it a component O_y, acting vertical, perpendicular to F_c (which you probably should be referring to as O_x instead of F_c).
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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