59 thoughts on “Homework 24.B”

    1. No. For 24.B's problem statement, the "Find" section does not ask for the answers in vector form. However, 24.A does ask for answers in vector form.

    1. Because AC is a multi-force member, there should be Cx and Cy acting on AC at C. If, for example, you choose Cx and Cy to act on AC in the positive x and positive y directions, respectively, then Cx and Cy should be acting on the other multi-force member, CE, in the negative x and y directions, respectively, by Newton's third.

    1. There is only one reaction force, the normal force at A, because there is a roller with no friction so there will not be a reaction force parallel to the surface. However, the normal force vector will have x and y components.

    2. There should be a normal force at A from the roller. You can also right it in Ax and Ay form but there would be a relation between Ax and Ay due to theta is 30 degree.

    1. Hi Kate,

      Yes. Unless specified, I don’t think we need to take into account the thickness and thus weight of the bar. We can simply assume that the forces applied are much larger than the weight of the bar itself. At least that’s what I’ll be doing in my calculations.

    1. Hi Mike,

      Because CE is a fixed support, it has to produce a reaction moment to prevent rotation. You still set the moment equation equal to 0 if taking it at E, but now you have to account for the reaction moment in the equation as well.

      1. Well, the moment equation would be set equal to zero regardless of where the moment is taken at. E does produce a reaction moment counter to the reaction on the system at A, that is true, but it counters the remaining moments throughout the system regardless of where they are calculated from.

    2. Hi Mike,

      It is important to remember that for fixed support, there exists three reactions - reaction in x, the reaction in y, and the moment reaction about the fixed point.

    1. Hi Noah,

      Yes, you are correct that cos(30) is for the y component and sin(30) is for the x component in this problem. Finding the x and y components for reaction forces on an incline can be tricky sometimes!

  1. When writing moment equations with the two different arm segments, do we include the applied force on the other arm? For example, if finding the moment about A, do we need to include force F, even though it's on the other arm segment?

    1. Hi Mehal,
      I split my structure into two parts. The first part is the entire structure from A to C, and the second part is the rest of the structure that is C to E. Because it is split into two, you do not need to include the applied forces acting on the opposite section of the structure in your moment equation.

    1. Hi Josh, I'm not sure if I have them all covered, but I have simply been putting constant forces, in static equilibrium, and 2 force members (if applicable). Are there any others that I could potentially be lacking?

    1. In 24.A it specially says to write in vector form, however it doesn't specially say that for 24.B. Personally, I wrote my answers for both problems in vector form.

    1. That's what I have. However, I'd be careful about how you calculate your moment. The pin joint at C changes how force P will affect the moment at point E.

  2. Remember there is is a Moment on the wall at point E, because it is a Fixed point. And the answer should be in terms of theta. The best way to do this problem is draw the individual free body diagrams for each component, and solve for the individual equilibrium equations. Just a hint

  3. If you draw two FBD's, one for each side of the joint, and the Cx reactions are equal and opposite, do you have to do a summation of Fx for the right FBD in your work to show that the Cx of the left will be equal to Ex, or can you just write that Cx of the right is equal to Ex.

    1. From the FBD, Cx will be equal to Ex because those are the only horizontal forces acting on the other member. If you've already solved for Cx in the first member, you can just indicate a summation of Fx that Cx is equal to Ex.

  4. Do we need to write our answers in vector notation? For example, the reaction at A can we just give what the normal force is or do we have to deconstruct it to its x and y-components?

Leave a Reply