Finding the contact force in a hinge?

AI Thread Summary
The discussion focuses on calculating the contact force in a hinge for a beam system in equilibrium. The user details their method for finding the tension in the wire and subsequently the hinge force, arriving at a tension of 293.02 N and a hinge force of 291.9 N at an angle of 24.5°. They seek verification of their calculations and clarification on the concept of equilibrium, specifically whether being in equilibrium at 20° means the system is not in equilibrium at other angles. The thread emphasizes the importance of understanding torque and force resolution in static equilibrium problems. Overall, the calculations and concepts presented are critical for solving similar physics problems related to forces in static systems.
SopwithCamel
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I have been working on a slightly tricky calculus problem and was hoping someone could verify my solution.

Homework Statement



A 4m long beam whose mass is 5 kg is attached to the wall by a wire and a hinge that allows the beam to rotate. There is a sign (with a mass of 20 kg) attached to the beam. The system is in equilibrium when the beam is at 20° to the horizontal. What is the contact force in the hinge (magnitude and direction)?

Homework Equations



The Attempt at a Solution



I first found the tension in the wire by setting the net torque to zero:
0=|r||T|sinθ + |rs||Fs|sinθ - |rb||Fb|sinθ
(where Fs is the force of the sign and Fb is the force of the beam and rs and rb is the distance of the forces from the hinge, respectively)
0=(4)(T)sin135 - (4)(196)sin110 - (2)(49)sin110
Solving for T, I get the tension in the wire = 293.02 N.

Then, to find the force in the hinge, I found two equations by resolving it into it's vertical and horizontal forces:
Horizontal: Tcos25 = Fcosθ ---> Fcosθ = 265.574N
Vertical: 0 = Fsinθ + Tsin25 - 49 - 196 ---> 245 = Fsinθ + 123.574N ---> Fsinθ = 121.161N

From there, I was able to solve... θ = 24.5° and F = 291.9N.


Is this correct? I hope this isn't asking too much... Please tell me if there are any errors in my figuring.

ALSO ... A quick question: When it says the beam is in equilibrium at 20° to the horizontal, does that imply that it is not at equilibrium at any other point? What exactly does it mean in this scenario to be "in equilibrium"?

Thank you!
 
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This isn't a calculus problem. I've moved the thread to the intro physics forum.
 
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