Free Body Diragram of a pulley

In summary, the problem is asking for free-body diagrams in three different cases for a figure with suspended blocks of weight w, frictionless pulleys, and negligible weight ropes. The correct free-body diagram for the pulley system is tension pointing up and weight (mg) pointing down, while the incorrect diagrams for the individual blocks have yet to be determined. Clarification from the teacher is needed.
  • #1
Goofball Randy
21
0

Homework Statement



In the figure (Figure 1) each of the suspended blocks has weight w. The pulleys are frictionless and the ropes have negligible weight.

YF-05-41.jpg

Homework Equations



w = mg
Forces cancel out, so Tension = weight (since they are suspended)

The Attempt at a Solution



For a (pulley) ), I tried a free-body diagram with mg pointing down, and tension pointing up, with equal magnitude. This was marked wrong, but I don't see any other forces acting on the weight.

For b (either weight) ), I did the same thing as I did in a, because, after all, isn't it just mg and tension that act on both weights?

For c (either weight) ), same as a and b.
 
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  • #2
Exactly what does the problem ask? To draw a free body diagram of the pulley? If so then why did you draw FBDs of the weights?
 
  • #3
Nathanael said:
Exactly what does the problem ask? To draw a free body diagram of the pulley? If so then why did you draw FBDs of the weights?

For part A, it's of the pulley system. B and C ask you to draw for one of the weights.
 
  • #4
Did you get B and C right? For A you described an FBD for the weight, not the pulley.
 
  • #5
Nathanael said:
Did you get B and C right? For A you described an FBD for the weight, not the pulley.

No, B and C are wrong as well :( That's why I don't understand, I would have thought it would just be tension and mg...
 
  • #6
Your teacher didn't explain why you got it wrong? I would ask him/her why you got B and C wrong. Do you know why you get A wrong?

Do you have the exact problem statement?
 
  • #7
Nathanael said:
Your teacher didn't explain why you got it wrong? I would ask him/her why you got B and C wrong. Do you know why you get A wrong?

Do you have the exact problem statement?

That is the exact problem statement. :(
In the figure (Figure 1) each of the suspended blocks has weight w. The pulleys are frictionless and the ropes have negligible weight.

In the case (a), draw the free-body diagram.
In the case (b), draw the free-body diagram of one of the blocks.
In the case (c), draw the free-body diagram of one of the blocks.

Word for word.

And this is one of those online assignments. I can't get any teacher feedback until the week begins.

The problem itself doesn't say whether it's wanting the pulley or the weight. But given that I've tried tension up, mg down, and that's incorrect, and I believe that to be the correct FBD for a suspended weight, I'm led to believe that it's asking for the pulley system...
 

Related to Free Body Diragram of a pulley

1. What is a free body diagram of a pulley?

A free body diagram of a pulley is a visual representation of the forces acting on a pulley. It shows the pulley as a single point and includes all the external forces acting on it.

2. What are the important components of a free body diagram of a pulley?

The important components of a free body diagram of a pulley include the pulley itself, the rope or cable attached to it, and any external forces such as tension, friction, or weight.

3. Why is it important to use a free body diagram when analyzing a pulley?

A free body diagram helps to simplify the analysis of a pulley system by isolating the forces acting on the pulley. This allows for a clearer understanding of the system and makes it easier to calculate the net force and resulting motion.

4. How do you draw a free body diagram of a pulley?

To draw a free body diagram of a pulley, start by drawing a dot to represent the pulley. Then, draw arrows to represent the forces acting on the pulley, with the direction of the arrows indicating the direction of the force. Make sure to label each force and include the magnitude of the force if known.

5. Can a free body diagram of a pulley be used to analyze both static and dynamic situations?

Yes, a free body diagram of a pulley can be used to analyze both static and dynamic situations. In a static situation, the forces will be balanced and the pulley will not be moving. In a dynamic situation, there will be unbalanced forces and the pulley will be in motion.

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