Tension on the String

  • #1
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?
 

Answers and Replies

  • #3
95
2
What are the forces acting on the middle block? Are they not only tension in B and tension in C?
 
  • #4
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Draw a free body diagram of the middle block. Show the forces acting on that block. What are they?

Chet
 
  • #5
DTM
62
6
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
phinds
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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
95
2
Ok, thanks. I got it now. The FBD on B should be T_b=T_c+Mg
 
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