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Homework Help: Radial acceleration around a planet

  1. Oct 17, 2008 #1
    1. The problem statement, all variables and given/known data

    Consider a planet of radius 7.31 x 10^6 m with a rotation period of 25.4 hours. Compute the radial acceleration of a point on the surface of the planet at the equator owing to its rotation about its axis.

    2. Relevant equations

    T = [2(pi)r]/v
    a_r = -[(v^2)/r]

    3. The attempt at a solution

    so i know one period (T) is 25.4 hours, and r = 7.31 x 10^6 m. so i use that and find velocity, and tried to plug that into the radial acceleration equation, but i got the wrong answer. what am i doing wrong? is it something to do with units of time?
  2. jcsd
  3. Oct 17, 2008 #2
    oh, and my answer was 2.88 x 10^8 m/s2
  4. Oct 17, 2008 #3

    D H

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    Staff Emeritus
    Science Advisor

    Did you convert the hours to seconds? If not, you are spot-on regarding time.

    That means you did something else wrong in addition to the time units error. Please show your work.
  5. Oct 17, 2008 #4
    25.4 hours = 91440 seconds = 2(pi)(7.31 x 10^6)/v
    so v = 502.3 m/s
    a_r = [(502.3 m/s)^2]/(7.31 x 10^6) = 0.0345 m/s^2

    would that be the right answer? it seems kind of small.
  6. Oct 17, 2008 #5

    D H

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    Staff Emeritus
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    Looks fine to me.
  7. Oct 17, 2008 #6
    thanks a lot D H.
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