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Homework Help: Physics Force and Motion Problem

  1. Feb 7, 2010 #1
    An interstellar ship has a mass of 1.20 x 10^6 kg and is initially at rest relative to a star system. (a) What constant acceleration is needed to bring the ship up to a speed of 0.10c (where c is the speed of light, 3.0 x 10^8 m/s) relative to the star system in 3.0 days? (b) What is that acceleration in g units? (c) What force is required for the acceleration? (d) If the engines are shut down when 0.10c is reached (the speed then remains constant), how long does the ship take (start to finish) to journey 5.0 light-months, the distance that light travels in 5.0 months?


    *If anyone could show the steps to the solution to this problem that would be great. I'm unsure of how to even begin.
     
  2. jcsd
  3. Feb 7, 2010 #2

    Redbelly98

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    Welcome to Physics Forums.

    (a) What is the relationship between a, Δv, and Δt?
     
  4. Feb 8, 2010 #3
    a = Δv / t-0
     
  5. Feb 8, 2010 #4

    Redbelly98

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    Yes. You can use that to solve part (a).
     
  6. Feb 8, 2010 #5
    so I would set:


    Δv = 3.0 x 10^8 m/s

    t = 3.0 days

    a = ?

    and putting that into the previously mentioned equation would equal: 10^8 m/s

    I feel like I did something wrong?
     
  7. Feb 8, 2010 #6

    Redbelly98

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    The only thing wrong is your units. The "days" from "3.0 days" should be included in the answer somehow.

    EDIT:
    Hold it, where did you get Δv = 3.0 x 10^8 m/s ???
     
    Last edited: Feb 8, 2010
  8. Feb 8, 2010 #7
    Would the units for part (a) be meters / day then?

    Now, for part (b) would I divide the acceleration from part (a) by 9.8 m/s^2?
     
  9. Feb 8, 2010 #8

    Redbelly98

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    Note: see the EDIT in my previous message.

    No. Think about the calculation you did.

    You start with Δv in units of m/s. Next you divide this by something with units of days. That gives units of ____?

    Yes, but first we must get a correct (a), including units.
     
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