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Work and Energy of water slide

  1. Oct 9, 2011 #1
    A student, starting from rest, slides down a water slide. On the way down, a kinetic frictional force (a nonconservative force) acts on her. The student has a mass of 70 kg, and the height of the water slide is 11.3 m. If the kinetic frictional force does -7.6 × 103 J of work, how fast is the student going at the bottom of the slide?

    Could someone tell me where I am going wrong with this problem?

    Vo = 0 m/s
    m = 70 kg
    Ho = 11.3 m
    Hf = 0 m
    Wnc = -7.6 x 103 J

    Wnc = 0.5m(Vf2 -Vo2) + mg(Hf-Ho)
    -7.6 x 103 = 0.5(70)(Vf2) + 70(9.8)(11.3)
    Vf = 20.9 m/s
     
    Last edited: Oct 9, 2011
  2. jcsd
  3. Oct 9, 2011 #2
    I think that only your answer is wrong. All the rest is OK.
    My answer is 2.08m/s
     
  4. Oct 9, 2011 #3
    I tried your answer. That is incorrect also....Eeek please help!
     
  5. Oct 9, 2011 #4
    That equation should have a positive sign in front of it....but still I get the answer wrong because my original answer is still 20.9 m/s
     
  6. Oct 9, 2011 #5
    I wasted an attempt with 2.08 m/s. I have one try left please somebody help!
     
  7. Oct 9, 2011 #6
    The tolerance allowed for this answer is +/- 2%. Does that mean I am just using the incorrect amount of significant figures ?
     
  8. Oct 9, 2011 #7

    Doc Al

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    Staff: Mentor

    Hf - Ho should be negative.
     
  9. Oct 9, 2011 #8
    With Hf - Ho = 0 - 11.3 = -11.3 meters, I get 2.08 m/s. This answer is still wrong according to the WileyPlus electronic homework submission site.
     
  10. Oct 9, 2011 #9

    Doc Al

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    Staff: Mentor

    I'd say that answer is correct. As far as your online homework system goes, it may be looking for a different number of significant figures.
     
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