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How much work must you do to push a 13 block of steel across a steel table at a ste

  1. Nov 24, 2009 #1
    How much work must you do to push a 13g block of steel across a steel table(coefficent of friction=.6) at a steady speed of 1.2 for 8.8 ?

    I know that Work=Force*Distance

    i know what the D is but i dont know how to calculate the force.
    i tried F=MA and got Fnet= Force pushed -Friction force
    i really have no i dea tho. I need help please.
     
  2. jcsd
  3. Nov 24, 2009 #2

    Doc Al

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    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Hint: What does 'steady speed' tell you about the net force?

    How do you calculate the friction force?
     
  4. Nov 24, 2009 #3
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Steady speed says the friction is constant and friction force is kinetic friction*normal force or Fk*mg mg= normal force i think
     
  5. Nov 24, 2009 #4

    Doc Al

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    Re: How much work must you do to push a 13 block of steel across a steel table at a

    OK, good. But what does Fnet equal? (What's the acceleration of the block?)
     
  6. Nov 24, 2009 #5
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    sorry its 13 kg 1.2 m/s and 8.8 s
     
  7. Nov 24, 2009 #6
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    the acceleration is zero because it is a constant velocity
     
  8. Nov 24, 2009 #7

    Doc Al

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    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Good. So what's Fnet? And what does that tell you about Fpush?
     
  9. Nov 24, 2009 #8
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Fnet is equal to zero since the acc. is zero. F push is equal to friction force?
     
  10. Nov 24, 2009 #9

    Doc Al

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    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Exactly! You should be able to calculate the work now.
     
  11. Nov 24, 2009 #10
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Fpush is equal to 0 and f net is equal to friction force

    so Fnet=Fpush+Ffriction
    Fpush=0
    Fnet=Ffriction
    Ffriction=Fnet =(.6)mg---->.6*13*9.8=76.44
    so
    Work=Fnet*D
    D = 1.2m/s*8.8s---->10.56 m
    so
    76.44*10.56=807.2 J
     
  12. Nov 24, 2009 #11
    Re: How much work must you do to push a 13 block of steel across a steel table at a

    Thanks for all your help : )
     
  13. Nov 24, 2009 #12

    Doc Al

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    Re: How much work must you do to push a 13 block of steel across a steel table at a

    No, you had it right before. Fnet = 0 so Fpush = Ffriction.

    No, but that doesn't affect your calculation, which is correct.

    It's the force Fpush that is doing the work.
     
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