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Work and energy without friction

  1. Apr 8, 2009 #1
    1. The problem statement, all variables and given/known data
    A physics student shoves a 0.50-kg block from the bottom of a frictionless 30.0° inclined plane. The student performs 4.0 J of work and the block slides a distance s along the incline before it stops. Determine the value of s in cm.


    2. Relevant equations

    W=(Fcostheta)s

    3. The attempt at a solution
    In the problem we have the weight of the block the degree of the incline and the work done. i was wondering how I would find F cause wouldnt W=4.0J cos=30.0.
     
  2. jcsd
  3. Apr 8, 2009 #2

    mgb_phys

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    The energy only depends on the vertical distance traveled.
    Find that from W=mgh and then simple trig gives you the distance along the slope
     
  4. Apr 8, 2009 #3

    Doc Al

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    Staff: Mentor

    Don't worry about trying to figure out the force that the student exerted (assuming that's what you mean by F). You don't have enough information and it's not needed anyway.

    Hint: Use conservation of energy.
     
  5. Apr 8, 2009 #4
    I did W=mgh
    4.0J=(0.50kg)(9.80)h

    Im still getting the wrong answer am i using the wrong equation or an error in my math
     
  6. Apr 8, 2009 #5

    Doc Al

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    That equation will give you the height, which is the first step. Now use a bit of trig (as mgb_phys said) to find the distance along the incline that corresponds to that height.
     
  7. Apr 8, 2009 #6
    i get 180 cm is this correct
     
  8. Apr 8, 2009 #7

    Doc Al

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    Staff: Mentor

    No. Show the steps you used to get that result.
     
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