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Real fundemental physics problems . Don't laugh!

  1. Aug 22, 2013 #1
    Real fundemental physics "problems". Don't laugh!

    ]1. The problem statement, all variables and given/known data[/b]

    A) A box is dragged on a leveled floor with a constant speed according to the picture below.

    [Broken]

    Decide what has been accomplished when the box has been dragged 4m.


    B) An object is moving from a stand-still position in A as the picture shows. What speed will it have once it reached point B if there is no fraction?

    [Broken]

    3. The attempt at a solution

    A) I have absolutely no idea.

    B) In this case there are/is two sorts of energy we need to take into account.

    Kinetic energy and potential energy.

    Kinetic energy = T=mv2
    Potential energy = V=mgh

    At this point, since we don't know the velocity of the object we can't use the kinetic energy so we put potential energy to work.

    Or when I think about it I don't think this makes sense. I need some formula to get the velocity of the object out of the energy it produces. Should I use the formula of potential energy and just put in a number for the mass of the object? First I thought that the mass of the object doesn't matter if there's no friction but after some research I found out a logical answer, the mass of the object will determine it's acceleration when in motion and therefore the greater the mass the greater the speed will be.

    Anyways as you can see I am kind of stuck between a rock and a stupid place.

    This is my 2 last problems I need to solve and I have to turn it in tomorrow morning that's why I post here, I've sat with several problems for hours on end today and yesterday and solved a lot of problems myself but some I just can't solve without any guidance. I am doing these problems without physics study-literature which is probably stupid but I can't rly afford to buy it until my "study-cheque" comes in next week.

    Any help is greatly appreciated.

    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Aug 22, 2013 #2
    First of all for part A there is a multitude of answers, some make more sense than others, it is a very open question.
    Part B is more specific from a physics point of view.....what do you know about potential and kinetic energy?
     
  4. Aug 22, 2013 #3
    I pretty much only knows the equations and what the variables mean in those equation. like v2 m,g etc.. I also think that kinetic energy means that the energy an object has is stored within that object so when an uphill comes the object releases as much energy as needed or what energy it has.

    About A) how do I go about to "solve" it then.
     
  5. Aug 22, 2013 #4

    PeterO

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    Homework Helper

    The accomplishment is that you have moved the box 4m - however if you dragged it in a circular path, an outside observer might not notice any change over all.

    Alternately: "You have proved yourself strong enough to overcome the friction between the box and the floor"
     
    Last edited by a moderator: May 6, 2017
  6. Aug 23, 2013 #5

    Borek

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    Staff: Mentor

    Have you heard about conserved quantities?

    I don't think it can be solved - wording is ambiguous. It can be "solved" - and PeterO already suggested several possible "answers".
     
  7. Aug 23, 2013 #6
    I appreciate the comments, although it turned out to be a solution for it.

    W = F*s
    W= 5*4 Nm = 20 Nm

    Although I have to say, my teacher formulated the problem kinda strange. Whatever, now I know until next time :)
     
  8. Aug 23, 2013 #7

    PeterO

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    That is certainly how much work is done against friction - but not much of an accomplishment.
     
  9. Aug 23, 2013 #8

    Borek

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    Staff: Mentor

    Last time I checked, Nm was J.
     
  10. Aug 23, 2013 #9
    Yeah, now when I took a second look at it I actually was the one who phrased it wrong, oops my bad.
     
  11. Aug 23, 2013 #10
    Okay, I had no idea lol I just wrote down what my teacher wrote as a solution.

    So basically anytime he writes Nm I can just use Joule myself? instead of being confused of the 2.
     
  12. Aug 23, 2013 #11

    Borek

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    Staff: Mentor

    Almost. Torque is measured in Nm, and my understanding is that to avoid confusion these should be not shortened to J (just like work should be not expressed in Nm).
     
  13. Aug 23, 2013 #12
    Okay so he did wrong by writing 20Nm because it should've been J in that specific case?
     
  14. Aug 23, 2013 #13

    Borek

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    Staff: Mentor

    Yes, that's my understanding.
     
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