Mechanics question on vector statics

AI Thread Summary
To determine the reactions at points B and D with b = 60mm, the discussion highlights the challenge of having four unknowns (Bx, By, Dx, Dy) but only three independent equations from static equilibrium. The user initially struggles to find a fourth equation, having established equations for horizontal and vertical forces and moments about point B. A suggestion is made to consider the forces at point C and to label the components of the system for clarity. Ultimately, the user confirms they found the solution after further analysis.
ashishsinghal
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Determine the reactions at B and D when b = 60mm ?
(Diagram is attached)

Since B and D are hinged we don't know the direction as well as magnitude of the reaction forces at B and D. Hence we have 4 unknowns (Bx, By, Dx, Dy).

But I can't find 4 independent equations. I got three by ƩFx= 0, ƩFy= 0 and moment about B = 0. Where is the 4th equation. Please help.
 

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hi ashishsinghal! :smile:

it's static, so what can you say about the forces at C ? :wink:
 
ashishsinghal said:
Determine the reactions at B and D when b = 60mm ?
(Diagram is attached)

Since B and D are hinged we don't know the direction as well as magnitude of the reaction forces at B and D. Hence we have 4 unknowns (Bx, By, Dx, Dy).

But I can't find 4 independent equations. I got three by ƩFx= 0, ƩFy= 0 and moment about B = 0. Where is the 4th equation. Please help.

Call the ABC piece number 1 and the CD piece number 2. You know the force at point A so you have six unknowns, the two components of force at points B, C and D. You have six equations:\sum F_{1x}=0\sum F_{1y}=0\sum F_{2x}=0\sum F_{2y}=0\sum \tau_1=0\sum \tau_2=0 where \tau is torque. (I assume "b" is not an unknown).
 
Thanks Rap I got the answer.
 
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