# Mechanics question on vector statics

1. Aug 10, 2012

### ashishsinghal

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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2. Aug 10, 2012

### tiny-tim

hi ashishsinghal!

it's static, so what can you say about the forces at C ?

3. Aug 10, 2012

### Rap

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).

4. Aug 14, 2012

### ashishsinghal

Thanks Rap I got the answer.