hi i need help to find these problems
I always tell my students that doing problems with variables is just like doing problems with numbers...all the manipulations are the same. However it does get to a point where you have so many variables that it becomes not only a tedious problem, but extremely messy and prone to errors.
The more information you can provide, the more likely we will be able to help you with this.
You either need to go to your professor and demand more information about the problem, or if this is a project you are constructing you need to come up with some more design constraints before you can reasonably expect to get an answer.
So not impossible to do, just difficult.
The mass of both bars
The angle each pushrod makes with each respective bar
The angle the two bars make with each other
The angle the bottom bar makes with the table (or whatever surface its attached to)
The length of the bottom bar
The positions of the point of contact between the bottom bar and both pushrods
(Total number of known unknowns: 10)
Now for the unknowns:
The force each pushrod is exerting on the respective bar
The two components of the reaction force on the pivot between the two bars**
The two components of the reaction force on the pivot between the bottom bar and the table
(Total number of unknowns: 7)
** Typically we resolve the reaction force on a pivot into perpendicular components which gives 2 unknowns for each pivot. (If we don't do this then the size and direction of this force are 2 unknowns anyway.) If we are lucky we don't have to solve for these, but in this case with two pivots we can't eliminate them from the equations so they have to be found.
This gives a total list of 17 variables. There are actually only 16 independent variables here: pushrod A exerts the same amount of force on the bottom bar as it does the top by a Newton's 3rd Law argument.
(This whole argument relies on frictionless pivots. If you need to include this factor as well then we've got 18 independent variables.)
Something just occurred to me. For the other two problems, we are given neither the outer nor the inner radius of the aluminum bar. These have to be taken into account in order to calculate the total stress the bar can take. So there's another two known unknowns in the problem.