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Homework Help: Conservation of energy problem involving a projectile.

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data

    An athlete putts a shot of mass 7 kg a distance of 20 m. Show that the athlete must do to
    at least 700 joules of work to achieve this. (ignore the height of the athlete.)
    2. Relevant equations[


    3. The attempt at a solution

    when the ball reaches maximum height, its velocity is zero. I should problem find the angle that gives the ball its maximum range. I am not sure how to find the angle that gives the ball its maximum range. maximum range is 20 meters.

    .5*m*v^2=mgz ==> v=sqrt(2gz)= 20 m/s

    R cos(theta)=v*u/g
  2. jcsd
  3. Oct 21, 2008 #2
    anyone not understand my question
  4. Oct 21, 2008 #3
    I understand the question. I don't understand your solution.

    The angle that gives maximum range is 45 degrees.
    Use this to find the initial speed. Then find kinetic energy.
  5. Oct 22, 2008 #4
    Isn't this introductory physics?
  6. Oct 22, 2008 #5
    "Isn't this introductory physics? "

    It depends on the reference frame. :wink:
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