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Homework Help: Help with an Energy Question please

  1. Feb 6, 2006 #1
    Hello. I'm stuck on this question. Any help would be appreciated:

    The orbit of the Earth about the Sun is almost circular. The closest and farthest distances are 1.47x10^8 km and 1.52x10^8 km, respectively. Determine the maximum variations in a) potential energy, b) kinetic energy, c) total energy, and d) orbital speed that result from the changing Earth-Sun distance in the course of 1 year.

    I got part a) no problem. However, I'm not sure about b), c) or d).

  2. jcsd
  3. Feb 6, 2006 #2
    You can easily calulate the velocity of the Earth at any arbitrary point on the ellipse:
    v = \left[ GM_sM_e\left(\frac{2}{r}-\frac{1}{a}\right)\right]^{1/2}
    and the total energy as
    E = -\frac{GM_sM_e}{2a}
    The semi major axis a for the Earth orbit is [itex]a = 149.6\cdot 10^6km[/itex]
    Last edited: Feb 6, 2006
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