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Homework Help: Keplers 1st Law

  1. Dec 30, 2012 #1
    1. The problem statement, all variables and given/known data
    Assuming that the sun lies at the principal focus of the solar system, and given that the semi-major axis and eccentricity of Mars is 1.5237 AU and 0.0934 respectively, calculate:

    The distance (in AU) when Mars is closest to the Sun (known as perihelion). The angle θ=0°

    2. Relevant equations

    r = a(1 - e^2) / (1 +e cos θ)

    3. The attempt at a solution

    The correct solution is 1.38 AU

    Though if I use the above eqn putting a=1.5237 and e=0.0934 I get an answer of 16.17.

    Thanks for any help!
  2. jcsd
  3. Dec 30, 2012 #2


    User Avatar

    Staff: Mentor

    Must be finger problems with the calculator :smile:

    What values do you calculate for the numerator and denominator of the expression?
  4. Dec 30, 2012 #3
    Sorry about that! I'm getting the correct answer now...!
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