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Homework Help: Conservation of Momentum of a Star

  1. Apr 8, 2010 #1
    1. The problem statement, all variables and given/known data

    Iota Draconis is the eighth brightest star in the constellation Draco. Observations show that a planet, with an orbital period of 1.50 y, is orbiting this star. The mass of Iota Draconis is 1.05MSun.
    (a) Estimate the size (in AU) of the semimajor axis of this planet's orbit.
    1.33 AU <--- This answer has been found

    (b) The radial speed of the star is observed to vary by 627 m/s. Use conservation of momentum to find the mass of the planet. Assume the orbit is circular, we are observing the orbit edge-on, and no other planets orbit Iota Draconis. Express the mass as a multiple of the mass of Jupiter.
    ____________ × mass of Jupiter

    2. Relevant equations
    m1v1 = m2v2

    [tex]\frac{m*v^2}{r}[/tex] = [tex]\frac{G*M*m}{r^2}[/tex]

    3. The attempt at a solution

    Let the equations equal each other, and you end up with:

    m2 = [tex]\frac{r * M * v^2}{G}[/tex]

    I'd just like to know if my math/thinking is correct so far. I should just be able to plug in numbers and get "m", right?
  2. jcsd
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