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Static friction, help!!

  1. Feb 25, 2017 #1
    1. The problem statement, all variables and given/known data
    In an automatic materials handeling operation, metal blocks of 1.5 kg each are pushed one at a time from bottom of a stack six blocks high. If the coefficient of friction is 0.25, determine the horizontal force required to push. There is a figure bellow.

    14880326036721501401957-jpg.113720.jpg

    I try to solve but my answer is different the offered solution. Don't know am i wronge or there is mistake in solution. Making me crazyy!!
     

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    Last edited by a moderator: Feb 25, 2017
  2. jcsd
  3. Feb 25, 2017 #2

    Nidum

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    Best to use the homework template .

    Anyway - show us what calculations you have done so far .
     
  4. Feb 25, 2017 #3

    PeroK

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    Welcome to PF. You need to post what you've done.
     
  5. Feb 25, 2017 #4
     

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  6. Feb 25, 2017 #5
    Sorry for color of paper!!
     
  7. Feb 25, 2017 #6

    Nidum

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    That is very hard to read . Please type out any further workings .

    How many block surfaces have friction force acting on them ?

    Is normal load the same for each surface ?
     
  8. Feb 25, 2017 #7
     

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  9. Feb 25, 2017 #8

    gneill

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    It's also not oriented correctly ?:)

    There's not many equations on it; It would be better to type them in thus making it easier for helpers to help you (while saving them from going blind and suffering a neck injury from turning their heads sideways to see what you've written o0) :smile:)
     
  10. Feb 25, 2017 #9
    As you can see on figure, 6 blocks each one 1.5 kg. Bottom one is always pushed meaning for sure after that happens another one will be put on top so that again they are six.
     
  11. Feb 25, 2017 #10
    I agree, just didn't know it flips the photo. Plus i am on phone not pc. Ill do again.
     
  12. Feb 25, 2017 #11

    PeroK

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    @Lily131313 You may be misunderstanding! In general, we can only help you by asking questions that guide you in the right direction. So, @Nidum wasn't asking because he didn't know, but because he wanted you to think about that aspect of the problem, as he may have seen where your mistake lies.
     
  13. Feb 25, 2017 #12
    Ok got ur point!! Hm lets try again then!
     
  14. Feb 25, 2017 #13

    Nidum

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    What I would like to see is a diagram showing what forces you think are acting on the block . You can safely assume that it's six blocks during the pushing out phase and that a new block is only added to the stack at a later time .
     
  15. Feb 25, 2017 #14
    Exactly. I thought as bottom one is always pushed all mass has to be sum as it is on top of frist one.

    Fw= mg= 6*1.5*9.81=88.29 N ⬇️
     
  16. Feb 25, 2017 #15

    Nidum

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    How many rubbing surfaces on the block being moved ?
     
  17. Feb 25, 2017 #16
     

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  18. Feb 25, 2017 #17
     
  19. Feb 25, 2017 #18

    Nidum

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    Draw a free body diagram for the moving block .
     
  20. Feb 25, 2017 #19
    If we assume that friction is the same up an down 0.25!
     

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  21. Feb 25, 2017 #20
    I got it!!!!! Thank you!!!!
     

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