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Throw a ball up how high does it go

  1. Apr 3, 2008 #1
    An object is projected straight upward from the surface of Earth with an initial speed of 2.98 km/s. What is the maximum height it reaches?


    Ok i know this seams like a really easy problem but i cant figure it out... since this question is from our chapter on gravity i have trued usuing is ke initial = potential energy final...
    ke initial being(1/2 m v^2) and potential energy final being: (GMm/r^2)^1/2 M is the mass of the earth and m is the mass of the ball
     
  2. jcsd
  3. Apr 3, 2008 #2
    You're not going to throw the ball so high that its distance to the center of mass of the earth will change by a significant percentage. g is nearly constant. Therefore PE at height h will be mgh.
     
  4. Apr 3, 2008 #3
    he said 2.98 km/s. that will get you high enough for g get significantly smaller.

    the potential energy for a mass at distance r from the earth is -GmM/r, if the potential at infinity is 0, so there is both an initial and a final potential energy.
     
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