Free Body Diagram Help: Homework Equations and Attempts

[USN2ENG]

Homework Statement

I feel that I am a bit fuzzy whether things are reaction forces. In the diagram I see there is a beam holding point B, and there are 3 forces: Cable BC, 500N, and 780N.

My professor wrote:
Ask yourself: is the beam holding the point from moving up or down, right or left? If so you will need to include the appropriate reaction forces in your FBD.

To me, it is, as the beam is not hinged. Unfortunately I am not quite sure how to handle how to label the reaction force. Any advice would be great!

Homework Equations

The Attempt at a Solution

My FBD is attached.

 

[Endorser]

At A, the reaction force is Upwards

 

[PhanthomJay]

When you draw a FBD of joint B, you must include ALL forces, both external and internal, acting on the joint. You neglected to include the force of the beam acting on the joint. You should also break down the applied external forces at B into their x and y components.

It is often best to find the reaction forces at A and C first, by using the 3 equilibrium equations and noting that the reaction force at C must be directed along the cable direction BC.

 

[PhanthomJay]

At A, the reaction force is Upwards

I don't see any reference to the weight of the beam, so I assume it is negligible, in which case there cannot be any upward force at A, since this is a pure truss with axial tensile or compressive forces only, in the cable and beam.

 

[DeeNos]

I can provide some guidance on how to approach this problem. First, let's clarify what a free body diagram (FBD) is. A free body diagram is a simplified representation of an object or system, showing all the external forces acting on it. It helps us analyze and solve problems involving forces and motion.

In this case, the object of interest is the beam holding point B. The three forces acting on it are the cable BC, 500N force, and 780N force. To create a FBD, we need to draw the object as a single point, and then add arrows to represent the forces acting on it. It is important to label each force with its magnitude and direction.

Now, let's address the issue of reaction forces. Reaction forces are forces that arise due to the constraints or supports of an object. In this case, the beam is holding point B, so there will be reaction forces at that point to prevent it from moving up, down, left, or right. These reaction forces are not explicitly shown in the given diagram, but we can label them as RBx and RBy, representing the horizontal and vertical reaction forces, respectively.

To determine the magnitude and direction of these reaction forces, we can use the principle of equilibrium, which states that the sum of all forces acting on an object must be equal to zero for the object to be in equilibrium (not moving). In other words, the net force in the x-direction (horizontal) and y-direction (vertical) must be zero. Using this principle, we can set up equations to solve for the reaction forces RBx and RBy.

In summary, to handle the reaction forces in this problem, we need to include them in our FBD and use the principle of equilibrium to determine their magnitudes and directions. I hope this helps with your homework and understanding of free body diagrams. Good luck!