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This homework

  1. Mar 3, 2007 #1
    w = Force times Distance
    w = FD

    4. A force of 100 newtons was necessry to lift a rock. A total of 150 joules of work was done. How far was the rock lifted??

    Please i really need to understand how to do this problem, if anyone reply's please try to give step by steps
     
  2. jcsd
  3. Mar 3, 2007 #2

    cristo

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    Well, I'm not going to do it for you! You have an equation with three variables. You know two of them, and want to find the third. How do you think you should do this?
     
  4. Mar 3, 2007 #3
    i tried forever but i can't find a way to do this.....so i have the force (100N) and i have the Work (150Joules) so i how can i get the distance
     
  5. Mar 3, 2007 #4

    cristo

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    You have the equation W=fd. Try rearranging this to make d the subject (i.e. to get d on its own). Can you do this?

    [Hint: What does the equation look like if you divide both sides by f?]
     
  6. Mar 3, 2007 #5
    so i would divide d to both sides so it would be w/d = f right?
     
  7. Mar 3, 2007 #6

    cristo

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    No; you want to find d.

    Did you read this?
     
  8. Mar 3, 2007 #7
    so f = 1.5 meters or newtons or joules
     
  9. Mar 3, 2007 #8
    No. The number is correct, but which one of those units do you mean, they are not equivalent.
     
  10. Mar 3, 2007 #9
    Ok i thought it was d......so the equation should look like this... W/F = D.....so 150/100 = f....f = 1.5 meters or Newtons or Joules?
     
  11. Mar 3, 2007 #10
    I made a mistake in my last post, you're correct in thinking it should be D, not f that is 1.5, but still it cannot be any one of those units they are not equivalent. So which is it newtons, meters or joules?
     
  12. Mar 3, 2007 #11
    "A force of 100 newtons was necessry to lift a rock. A total of 150 joules of work was done. How far was the rock lifted??"

    F=100N, right?
    W=150J, right?

    If W=FD, and you have F and W, but want to know D, set rearrange the equation to isolate the D.. W/F=D.. 100N/150J=1.5 meters.

    Why 1.5 METERS? Well, Newtons is a metric unit, and Joules is a metric unit.. And the metric unit for distance is meter. Or.. you could expand the newtons and joules..

    Newton=kg*m/(s^2)
    Joule=kg*(m^2)/(s^2)

    Back to the problem.. [100*kg*m/(s^2)] / [150 kg*(m^2)/(s^2)]
    That should result in 1.5, and all the units except meters cancel out, therefore, 1.5 meters.
     
  13. Mar 3, 2007 #12
    Please don't provide complete solutions to homework problems.
     
  14. Mar 3, 2007 #13
    He and everyone else has pretty much solved it already, I'm just explaining "concepts" and "theory" so that he'll understand why the answer has to be in meters.
     
  15. Mar 3, 2007 #14

    cristo

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    The OP had the correct numerical answer, however had not answered d_leet's question re the units. Besides, check out the PF guidelines: https://www.physicsforums.com/showthread.php?t=5374
     
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