1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Length of one day on another planet

  1. Apr 10, 2016 #1
    1. The problem statement, all variables and given/known data
    Imagine another planet with an acceleration of 10m/s^2 at its equator when ignoring the rotation of the planet. The radius of the planet is 6.2 x 10^6m. An object dropped at the equator yields an acceleration of 9.70m/s^2. Determine the length of one day on this planet.
    r=6.2x10^6m
    g=9.70m/s^2
    a=10m/s^2--> I don't know why we were given the first acceleration, I don't think it's equal to ac.

    2. Relevant equations
    I used Fc=4pi^2mr/T^2 and isolated for T.

    3. The attempt at a solution
    I used the above equation, plugging in mg for Fc because I think the force of gravity is the centripetal force. The 'm' variables cancelled out since I just divided them out. Then, I plugged all of my other given values in and solved for T. Since T is the time it takes in seconds to complete one revolution, I divided my result by 3600 to get the time it takes in hours to complete one revolution. My final answer was about 1.3hours. However, the book's answer is 7.9hours. I don't know where I went wrong
     
  2. jcsd
  3. Apr 10, 2016 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Fgravity does more than keep a person in a cicular orbit. It also keeps his feet on the ground .... with a given force mg.
     
  4. Apr 10, 2016 #3
    But the formula I used just asked for Fc
     
  5. Apr 10, 2016 #4

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    So ?
     
  6. Apr 10, 2016 #5

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If a person with a mass of 80 kg stands on a scale, the scale will show 80 x 9.7 kg, so the scale will push up with 776 N. Where does that force come from ?
     
  7. Apr 10, 2016 #6
    It's the force of gravity, but how is that important in centripetal acceleration?
     
  8. Apr 11, 2016 #7

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If the planet wouldn't rotate, what would the scale indicate ?
     
  9. Apr 13, 2016 #8
    Apparently you have to subtract the acceleration of the dropped object from the acceleration of the planet
     
  10. Apr 14, 2016 #9

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Is that understandable ?
     
  11. Apr 27, 2016 #10
    I don't understand why you're supposed to do that, but that's what my teacher said
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Length of one day on another planet
  1. Another one (Replies: 3)

  2. Another one (Replies: 7)

  3. Another one (Replies: 4)

Loading...