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Circular Motion of a ball around the earth

  1. Oct 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Calculate thow long it would take a ball to orbit the earth once , just above the surface , at a speed of 7920 ms^-1 . The radius of earth is 6400km.


    2. Relevant equations
    Well Im not sure to be honest.


    3. The attempt at a solution
    I tried using S=ut+1/2(a)(t)^2

    Then used (-b +/- √b^2-4ac)/2a

    But got stuck in (-b +/- √b^2-4ac)/2a because got a negative sign answer in the √

    Cant find a formula in the book for this - probably have to manipulate some other formulas, but as I said im not sure
     
  2. jcsd
  3. Oct 3, 2010 #2
    If you know the radius of the earth, you can calculate the circumference.

    You know the speed of the ball.

    With those two pieces of data you can calculate the time taken to complete the journey:

    Time = Distance / Speed

    No need for SUVAT equations here.

    Jared
     
  4. Oct 3, 2010 #3
    Thanks alot Jared - I feel dumb now for using SUVAT lol

    -PsyG
     
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