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Astronomy/Kepler Law Question that is KILLING me.

  1. Sep 21, 2006 #1
    For some reason, I just can't seem to get this problem right even though I go through it tons of times and I earnestly believe that my answer is correct, but I guess not.

    http://img.photobucket.com/albums/v45/takomastock/640ddd43.jpg" [Broken]

    "Use Kepler's Laws to determine the comparison between various items shown in the figure. Assume the figure is drawn to scale.
    (Select G-Greater than, L-Less than, E-Equal to, If the first is G and the rest E, enter GEEEE)."

    A) A planet with half the average distance to the star would have ..... half the period.
    B) If area 1 and 3 are equal the time to go from D to E is ..... the time to go from A to B
    C) The speed at A ..... the speed at D
    D) The planets's average speed between D and E is ..... the average speed between A and B
    E) Time to go from B to C is ..... time from A to B

    I've come up with all these answers and all are wrong. I even narrowed it down to believe that the last 4 answers are "EGLE", but it seems it's wrong.

    These are all the possibilities I've come up with, and nope. Still incorrect.









    Please freaking enlighten me. :cry:
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 21, 2006 #2
    1) T^2 = a^3 so as the semimajor axis is cut in half...the period moves down faster than half (L)
    B) they must be the same because equal areas are swept out during equal times. (E)
    C) (G) seems you understand this
    D) Look at the distance traveled in the same period of time...also, when an orbiting object is closer, its average speed is increased(L)
    E) the object's speed slows down as it moves away(G)

    I believe this is correct...please correct me if i'm wrong
    Last edited by a moderator: May 2, 2017
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