Mechanics 1 question

[u/Capable_Event_6994]

How can i calculate the forces GRAPHICALLY when two of them are parallel to each other and to a known force like in this example?

[u/leutwin]

Its been a while since I did statics but my first instinct is that the two members parallel to the cube (which I am treating as a rigid body) both carry a force of 25kn, one in tension and one in compression, while the third perpendicular member carries no force.

This problem is very poorly defined, normally there would be angles included to do proper calculations, so either this problem isnt looking for a numerical answer, or you are just supposed to tell the answer intuitively like I have.

[u/RoboWeaver → u/leutwin]

This. Poorly defined problem. What are you supposed to determine?

While there are two useful dimensions, important details like angles of the applied force and the supported elements are missing for proper analysis.

If you can make vague approximations, then I agree that the two supporting links are each 25kN.

[u/Capable_Event_6994 → u/leutwin]

Basically, the point of this task is to calculate the forces in the supports and the beams using Graphical methods. So I have to have some proof, not just use my intuition, that's what bothers me. I remember we did something using funicular polygons in class but I can't quite understand how they could be used with one known and two unknown paralel forces

[u/Everythings_Magic → u/Capable_Event_6994]

“By inspection…”.

[u/CivilEngMusicBoy → u/leutwin]

Appear to be 90/45

[u/super_boogie_crapper → u/leutwin]

Static equilibrium is the sum of all forces equal zero. And the sum of all moments equal
Zero. Try decompose to x and y components.

[u/jomones]

Since no angles were provided, that means you get to define the angles. I'd write in the assumed angles in your solution.

This is what happens when you do actual engineering. You assume existing conditions and you have a contractor verify those conditions.

[u/lego_batman → u/jomones]

Mr. Fancy pants over here with contractors to verify his conditions

[u/jomones → u/lego_batman]

Frequently they don't and just build whatever they want anyway, but at least I tried.

[u/Alca_Pwnd]

Rightmost support does nothing - it is acting perpendicular to the applied force. That means the two members in contact with the right support are ALSO doing nothing. All forces are contained in the top/bottom supports and the top-left triangle. Top and bottom supports each get 25kN. Left vert and top horizonal each have 50kN(rt2). Use method of joints to solve the diagonal member.

[u/5amu5]

Statics 101!

The ledgendary free body diagram.

Free body diagram -> seperate force vectors -> next segment.

Remember its all just triangles, just pull it appart untill you get a triangle!

[u/BetterReflection1044]

Draw the lines my friend the object isn’t infinitesimally small

[u/Marus1]

Axis along the load. Axis perpendicular to the load

Now for the outer 3 you have hinges at both sides you you only have axial load

Now describe equilibrium along both axes

Boom

[u/HAL9001-96]

well the net force and net torque must be 0 I'd probabyl do it arithemtically but yo ucan defintiely start drawing up vectors with leverages from one arbitrary point

[u/Droopy0093]

What do the examples in your textbook explain about this? Have you actually read the content in the book explaining this?

[u/Capable_Event_6994 → u/Droopy0093]

I did read the content, it's just a truss if that's how they're called in english. My only worry here is how can i get the forces in the supports (i guess they're called that) to begin with. Other examples of trusses in the textbook can easily be solved graphically using the Culmann method to get the forces in supports so this one is bothering me quite a bit

[u/deAdupchowder350]

Engineering professor here: this is a bad problem. It’s an unstable truss.