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Blocks and Pulleys Problem, please help!

  • Thread starter FabricWarp
  • Start date
  • #1
Three Blocks total, Two on sides hanging off the table, and one Block on table in the middle of the two outer blocks. . . symmetrical.

block1 from left has a mass of M, hanging and connected to a pulley, which is the connected to Block 2(on a table) with Mass of 2M, Block three is also hanging but with mass of 2M. If acceleration is .5m/s^2, What is the Tension on the first string?
what is the Kinetic friction of Black 2 on Table?

Fnet=Ma

I started by writing that Block 3= 2Mg-T2=2Ma
Block 2= T2-T1=2Ma
Block 1= T1-Mg=Ma
I then connected Block3 to Block2, since they share T2
I would add forces but tensions would simply cancel out, at times even masses and Tension, leaving me with known variables=known variables, makes not sense. I tried many ways. This is all the info the book gives, but I feel I'm missing a key idea.


This has been driving me insane.
The tension question was given to me on a test, which I failed answering correctly.
The Kinetic question, I know from back of book, the coefficient of kinetic friction is = .37
But I don't know how exactly how they got to it. Some one please help.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
Doc Al
Mentor
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1,206
I started by writing that Block 3= 2Mg-T2=2Ma
Good.
Block 2= T2-T1=2Ma
Don't forget that friction acts on Block 2.
Block 1= T1-Mg=Ma
Good.

Correct your equation for Block 2 and you'll be able to solve for the friction, then use that to find μ.
 
  • #3
tiny-tim
Science Advisor
Homework Helper
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Welcome to PF!

Hi FabricWarp! Welcome to PF! :smile:

(instead of using "SIZE" tags, try using the X2 and X2 tags just above the Reply box :wink:)
Block 2= T2-T1=2Ma
ooh, you're missing the obvious … you need a 2µMg somewhere in there, don't you? :smile:
 

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