Pulley and Pins on a Frame (beginner statics)

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Homework Statement


upload_2018-5-4_17-23-59.png


Homework Equations




***i posted the questions and my free body diagrams below

The Attempt at a Solution


Hi. I'm trying to analyze this structure particularly at points C and B.

when drawing the free body diagram, i notice there would be pin forces on C as well as B. Also, there are the tension forces from the rope.

Am i suppose to draw all these out? How would i show the reaction forces on the other free body diagram. Would i write the reaction forces of the pin forces as well as the tension forces?
 

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  • #2
BvU
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HI, I see a nice picture but no problem statement ! "analyze" is more like a mission statement than a problem statement :rolleyes: . Any givens ? Pulley radii ?
Am I supposed to draw all these out?
I can't read the exercise composer's mind from here.
How would i show the reaction forces on the other free body diagram
What other diagram ? I don't even see the one, let alone the other !
 
  • #3
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HI, I see a nice picture but no problem statement ! "analyze" is more like a mission statement than a problem statement :rolleyes: . Any givens ? Pulley radii ?
I can't read the exercise composer's mind from here.
What other diagram ? I don't even see the one, let alone the other !
Oops. I left out the important stuff!
upload_2018-5-4_17-58-16.png

The question wants me to find reaction forces at supports D and A
What i mean was how i would go about breaking apart the frame into separate free body diagrams
 

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haruspex
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The question wants me to find reaction forces at supports D and A
Then you should not need to get into details of forces on the pulleys. Just treat ABC and its pulleys as one body. You can include the sections of rope in contact with the pulleys and between the pulleys.
 
  • #6
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Then you should not need to get into details of forces on the pulleys. Just treat ABC and its pulleys as one body. You can include the sections of rope in contact with the pulleys and between the pulleys.
Thank you. I'll be back with a new diagram and hopefully the correct answer!
 
  • #7
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Then you should not need to get into details of forces on the pulleys. Just treat ABC and its pulleys as one body. You can include the sections of rope in contact with the pulleys and between the pulleys.
Thanks so much. I was able to get the correct answer. Ughh, this took a while for me to figure out! I didn't know i didn't have to draw the pulley...I kept getting the wrong numbers with that.
 
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I was able to get the correct answer
Out of curiosity: did you have to assume pulley C has diameter zero ? I can't find the torque of ##\bf P## around A if I cannot make that assumption.
 
  • #9
haruspex
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Out of curiosity: did you have to assume pulley C has diameter zero ? I can't find the torque of ##\bf P## around A if I cannot make that assumption.
Yes, I noticed that but decided it did not matter.
If we treat the straight sections of rope and the forces they exert as all separate then the two pieces touching a pulley exert a net force which passes through the centre of the pulley. The magnitudes, directions and lines of action are independent of the pulley radius, and we can notionally shrink them all to zero.
 
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