Problem statements
Solution video – H21.A
Solution video – H21.B
DISCUSSION THREAD
Please post questions here on the homework, and take time to answer questions posted by others. You can learn both ways.
HOMEWORK 21 – Summer 25
11 thoughts on “HOMEWORK 21 – Summer 25”
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Is D a pin joint, and A a pin joint on wheels (no y reaction)?
I’m treating D as a pin joint (assumption given from the lecture) and r as a roller joint.
Yes, this should be correct. Example 2 on Brightspace (Period 18) showcases a similar setup, with the corresponding joints, point A only exerts a normal force in the +x direction, while point E (Point D in our case) has x and y force components.
Yes D is a joint, while A is supported with a roller as shown in the figure.
Example 2 on Brightspace had similar joints in the same orientation as the homework and could help understand how to set up this problem.
I think you would first solve the external force loads using equlibrium equations then use those values for the method of joints.
You can solve this problem just by looking at the reactions at some of the joints. Hint: You do not need to solve for the reactions at point D.
Like others have said, I also found “Method of Joints – Ex 2 (EXTRA)” in Lecture 18 to be helpful in solving this homework.
Two things
Firstly I solved for only three joints to get the 5 members, is that enough or would I have to show work for all 4 joints to get full credit?
Secondly, along with example 2 lecture 18(which many people said is a good example), Example 7.C.2 pg 270 in the book is a great reference for this hw as well.
That should be enough. You do not need to analyze every joint if you find it is not necessary.
I was able to solve the problem by solving for joints A, B and C, and used the bigger right triangle shape to solve for the components for force CD