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Homework Help: Finding Force by using the coefficient of friction and mass

  1. Oct 10, 2018 #1
    1. The problem statement, all variables and given/known data
    A man pushes a 50 kg box up a 20-degree ramp at constant velocity. If the pushing force is parallel to the ramp, and the coefficient of friction is 0.4, how much force is he pushing with?

    2. Relevant equations
    u=Fs, max/Fn Not sure if this equation is needed.

    3. The attempt at a solution
    I tried to solve the problem but I ended up getting the frictional force instead of the force he is pushing with.
     
  2. jcsd
  3. Oct 10, 2018 #2

    gneill

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    Staff: Mentor

    Show us the details of what what you've tried so far.
     
  4. Oct 11, 2018 #3

    CWatters

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    Make a free body diagram.
     
  5. Oct 11, 2018 #4
    Forces parallel to ramp mgsin(θ) and μFn. The man is pushing against weight component down the slope and friction.
     
    Last edited: Oct 11, 2018
  6. Oct 11, 2018 #5

    kuruman

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    Is that all?
     
  7. Oct 11, 2018 #6

    ZapperZ

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    What you wrote here does not qualify as "attempt at a solution". You told us you couldn't do it (which is automatic when someone posts something in this subforum), but without seeing what you actually did, there is no way anyone can diagnose what you did wrong.

    We are not allowed to give you outright solutions. We are, however, allowed to help you find the solution. And to do that, we need to know what you actually did. So show your work, especially your free-body diagram, as has been suggested.

    Zz.
     
  8. Oct 11, 2018 #7
    Yes.
     
  9. Oct 11, 2018 #8

    kuruman

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    What about the man pushing?
     
  10. Oct 11, 2018 #9
    As mentioned in my post, the man is pushing against the above-mentioned forces and there will be zero resultant force since the block does not accelerate.
     
  11. Oct 11, 2018 #10

    kuruman

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    I agree that the resultant force is zero. I disagree about the number of forces acting on the block. I can count 3 in the direction parallel to the incline that should add to zero: pushing force by man, friction by incline, component of gravity. How many are there according to your count?
     
  12. Oct 11, 2018 #11
    Quite right - there are 3 forces in equilibrium so the OP will need to add two of them to obtain the third. Or alternatively add all 3 and set equal to zero with the pushing force being the unknown.
     
  13. Oct 11, 2018 #12

    kuruman

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    You got it! :smile:
     
  14. Oct 12, 2018 at 9:47 AM #13
    More importantly I hope the OP did too!
     
  15. Oct 13, 2018 at 2:18 PM #14
    Thank you all for trying but I ended up going to the teacher to ask how to do the problem and I understand how to do the question. What I did wrong was that when I was trying to find the force, I used COH instead of TOA. Sorry for the inconvenience.
     
  16. Oct 14, 2018 at 1:59 AM #15
    Perhaps this was the correct response to the OP's query! I'm not sure what either COH nor TOA mean.
     
  17. Oct 14, 2018 at 12:04 PM #16

    jbriggs444

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    "COH" and "TOA" are apparently intended to be part of "SOHCAHTOA", which is a mnemonic for remembering how sine, cosine and tangent are found in a right triangle.

    http://mathworld.wolfram.com/SOHCAHTOA.html
     
  18. Oct 16, 2018 at 12:38 AM #17
    Thanks for the clarification.
     
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