physics

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It takes Pluto a longer time to travel around the sun than the Earth because Pluto:

a. has farther to go
b. goes slower
c. a and b
d. none of these

  • physics -

    Assume circular orbits.
    Now let me see
    F = Mplanet a where a is v^2/r, the centripetal acceleration with speed v and orbit radius r
    F = G Msun Mplanet /r^2
    so
    Mplanet v^2/r = G Msun Mplanet/r^2
    or
    v^2 r = G Msun for every planet around sun (I am calling Pluto a planet :)

    circumference of orbit = 2 pi r

    so time around T = 2 pi r/v

    but v = sqrt(G Msun/r)
    SO
    as r goes up, T goes up
    and as r goes up, v goes down
    SO
    it goes further, and it goes slower.

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