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Homework Help: Circular Motion of earth's orbit Problem

  1. Sep 23, 2010 #1
    Hello everyone! Please, help me understand the following problem:

    1. The problem statement, all variables and given/known data
    Earth's orbit around the Sun is nearly circular. The period is 1 yr = 365.25 d.
    (a) In an elapsed time of 5 d, what is Earth's angular displacement? Solved!
    (b) What is the change in Earth's velocity, Δv? Confused!

    2. Relevant equations
    ω = Δθ/Δt
    v = rω

    3. The attempt at a solution
    I easily solved the first problem doing this: Δθ = (2π x 5 days)/365.25 days = 0.0860 rads
    However, whenever I enter a solution for the second problem, the computer does not accept my answer, even though I'm solving it correctly. This is what I did:
    First, I tried to solve for the angular velocity of the object. Since the computer wants the answer in meters per second, I converted Δt to seconds:
    ω = Δθ/Δt = 0.0860121192 rads / (5 days x 86,400 sec) = 1.99x10^-7 rads/sec
    Now, I substitute the distance between the sun and the earth in meters and the angular velocity into v = rω to solve for v.
    v = rω = (1.5x10^14 m)(1.99x10^-7 rads/sec) = 2.99x10^7 m/s
    The correct answer, according to the computer, should be 2570 m/s.
    What am I doing wrong? :cry:
  2. jcsd
  3. Sep 23, 2010 #2
  4. Sep 23, 2010 #3
    Are you sure? That's similar to what I did, and that's not the answer, as I stated above.
  5. Sep 23, 2010 #4
    its 2 days over there in the link i gave

    and its 5 days in your case

    just make the adjustments
  6. Sep 24, 2010 #5
    Well... I exactly followed their whole procedure. I'm getting the wrong answer still, the correct answer should be 2570 m/s. Thank you for the link though! Anyone else? Help :cry:
  7. Sep 24, 2010 #6
    well may be the answer what u think is right is wrong :biggrin:
  8. Sep 24, 2010 #7
    I am coming to that conclusion :approve:. However, before telling my professor, it would be nice if someone in the Physics Forums could check my work and OK it first, if that's alright. o:)
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