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Homework Help: Energy bike problem

  1. Mar 15, 2010 #1
    1). Shawn and his bike have a total mass of 45.0kg. Shawn rides his bike 1.80km in 10.0 min at a constant velocity. What is Shawn's kinetic energy?

    m=45.0kg (Shawn+Bike total mass)
    t=10.0min-->600sec
    d=1.80km-->1,800m

    K=1/2mv^2.
    so...K=1/2(45.0kg)(???)^2

    I'm assuming v=3m/s

    Therefore v=3.0m/s?
    ---------------------------------------------------------------------------------------------------------
     
  2. jcsd
  3. Mar 15, 2010 #2

    Filip Larsen

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    Almost got it. You got speed from distance and time (no need to assume 3 m/s, calculate it!), and then you insert this speed into the equation for kinetic energy you correctly quoted.

    If you are confused about why the kinetic energy can be constant with Shawn pedalling along, you may want to think about where all the energy his muscles release end up when its not going into increasing his speed (hint: what happens if he stops pedalling and why does that happen).
     
  4. Mar 15, 2010 #3
    So, did I complete the problem correctly?
     
  5. Mar 15, 2010 #4

    Filip Larsen

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    You didn't give any final answer. The question is what Shawns kinetic energy is, that is, the value of the formula for K you gave. In your post you inserted the mass in this formula but did not insert the speed. Insert that and calculate the result and you have your answer (which should also include a correct physical unit for energy).
     
  6. Mar 15, 2010 #5
    Thank you. And the unit for energy is Joule (J).
     
  7. Mar 16, 2010 #6
    Is the answer 202.5J correct?
     
  8. Mar 16, 2010 #7

    Filip Larsen

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    Yes, that is correct.
     
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