Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Circular Motion (Orbiting Objects)

  1. Dec 14, 2011 #1
    1. The problem statement, all variables and given/known data
    *Part 1*
    A satellite is in a circular orbit 4000 km above
    the Earth’s surface; i.e., it moves on a circular
    path under the influence of nothing but the
    Earth’s gravity. Find the speed of the satellite. The radius of the Earth is 6.37 x10^6 , and the acceleration of gravity at the satellite’s altitude is3.71055 m/s^2.
    Answer in units of km/s

    *Part 2*
    Find the time it takes to complete one orbit
    around the Earth.
    Answer in units of s.

    2. Relevant equations


    3. The attempt at a solution

    For part one, I used a=v^2/r (3.71055=v^2/(6.37x10^6+4,000,000) and then converted it to km/s. I got 3.84784035 km/s which was wrong. Am i doing something wrong?

    I also have no idea how to do part 2 :(
    Last edited: Dec 14, 2011
  2. jcsd
  3. Dec 14, 2011 #2


    User Avatar
    Homework Helper

    I got nearly twice that. Take time to solve it for v on paper before keying it in!
    I don't see a part 2.
  4. Dec 14, 2011 #3
    Did I use the correct equation? And sorry about that, I just labeled part 2!
  5. Dec 14, 2011 #4


    User Avatar

    Staff: Mentor

    You've used a correct equation, but you didn't finish; you solved for v2, not v.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook