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Homework Help: Kinetic Energy Problem

  1. Jun 29, 2011 #1
    Q: A young Mr. Watford applies a force of 180N to a refrigerator on. kitchen floor.

    Part (A):Find the net force on the refrigerator if the floor has a constant frictional force of 35N.

    Ans:145N

    Part (B): Calculate the acceleration of the refrigerator if it has a mass of 70kg.

    Ans: 2.57 ms-2

    Part (C) Calculate the kinetic energy of the fridge after it has been pushed 5.00m.

    initial velocity = 0 ms-1
    displacement = 5m
    acceleration = 2.57 ms-2
    mass = 70kg
    time = ?


    s = ut + 1/2at^2
    v = u + at
    Ek=1/2 mv^2


    Substituting the given units into s = ut + 1/2at^2, I got time = 1.97s

    Substituting the units into v = u + at, I got final velocity = 5.06 ms-1

    And finally subbing the units into Ek= 1/2mv^2, I got Kinetic Energy = 896.13J.

    I got one benefit of the doubt mark out of four possible marks, and if that was in an exam I would've got 0 marks as there are no benefit of the doubt marks.

    Please reply asap I have an exam tomorrow.

    Thanks

    *ANSWERED*

    E = W
    W= Fs
    =180 x 5 = 900J
     
    Last edited: Jun 29, 2011
  2. jcsd
  3. Jun 29, 2011 #2

    SteamKing

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    Staff Emeritus
    Science Advisor
    Homework Helper

    Give us the entire problem statement, and you might get some constructive suggestions.
     
  4. Jun 29, 2011 #3
    Fixed! :)
     
  5. Jun 29, 2011 #4

    gneill

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    Staff: Mentor

    Rethink your calculation for the acceleration. The mass of the fridge will respond to the net force applied to it.
     
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