What's Wrong with My Force Analysis in These FBDs?

In summary, the conversation is discussing a physics problem involving a system of blocks connected by strings. The original attempt at a solution was incorrect and the discussion focused on correctly identifying the forces acting on each block and correcting the FBDs. The final conclusion is that the tension on B should be equal to the sum of the tension in C and the weight of the block.
  • #1
minimario
95
2

Homework Statement


bKy7FZm.png


Homework Equations


F=ma

The Attempt at a Solution


A FBD on the bottom block gives tension in C is equal to Mg. Then, a FBD on the middle block should give T_b-T_c=0, so tension on B should also be equal to Mg. Finally, a FBD on the top block gives the tension on A is equal to Mg.

But this is not correct, what did I do wrong?
 
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  • #2
minimario said:
... so tension on B should also be equal to Mg.
Really? You might want to rethink that.
 
  • #3
What are the forces acting on the middle block? Are they not only tension in B and tension in C?
 
  • #4
Draw a free body diagram of the middle block. Show the forces acting on that block. What are they?

Chet
 
  • #5
For your 2nd FBD, on the middle block, you forgot to include the Weight of that block. Same for the FBD on the top block.
 
  • #6
minimario said:
What are the forces acting on the middle block? Are they not only tension in B and tension in C?
Yes, but how does that relate to the answer to the you are looking for. Are you looking for the forces on a single block or the tension on the various strings? Suppose B was a rigid rod instead of a string. What would that do to your perception of the tension in string A ?
 
  • #7
Ok, thanks. I got it now. The FBD on B should be T_b=T_c+Mg
 
  • Like
Likes Chestermiller

FAQ: What's Wrong with My Force Analysis in These FBDs?

What is tension on the string?

Tension on the string refers to the force that is applied to a string when it is stretched. It is the pulling force that keeps the string taut and is typically measured in units of newtons (N).

How is tension on the string calculated?

Tension on the string can be calculated using the formula T = F * L, where T is the tension in newtons, F is the force applied to the string, and L is the length of the string. This formula assumes that the string is uniform and has a constant cross-sectional area.

What factors affect tension on the string?

Some factors that can affect tension on the string include the amount of force applied, the length and thickness of the string, and the properties of the material the string is made of. Additionally, any external forces acting on the string, such as gravity or friction, can also affect the tension.

How does tension on the string affect the sound produced by a musical instrument?

Tension on the string plays a crucial role in determining the pitch and tone of a sound produced by a musical instrument. A higher tension on the string will result in a higher pitch, while a lower tension will produce a lower pitch. The amount of tension also affects the quality and richness of the sound produced.

Can tension on the string be adjusted?

Yes, tension on the string can be adjusted by either changing the force applied to the string or by altering the length or thickness of the string. This is commonly done in musical instruments by tuning the strings to the desired tension for a specific pitch or sound quality.

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