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Homework Help: Physics 20 - Word Problems

  1. Sep 11, 2010 #1
    1. The problem statement, all variables and given/known data

    If a plane can travel 2.00 x 10^3 km in 3.00 hours, what is its velocity in m/s?

    2. Relevant equations

    3. The attempt at a solution

    V =
    d = 2.00 x 10^3 km
    t = 3.00h

    V = 2.00 x 10^3 km / 3.00h

    V = 2000km / 3.00h

    V = 666.67km/h

    666.67 kilometers = 666 670 meters - 666.67 hours = 2 400 012 seconds
    I'm not sure what to do at this step changing it to m/s

    V = ?m/s
  2. jcsd
  3. Sep 11, 2010 #2


    Staff: Mentor

    When you are converting between different units remember that you can always multiply by factors of 1. E.g.

    [tex]\frac{1 min}{60 s}=1[/tex]

    If you pick your factors of 1 correctly you can get the units you don't want to cancel out and just leave the units you do want. E.g.

    [tex]120 s = 120 s \; 1 = 120 s \frac{1 min}{60 s} = 2 min[/tex]

    Notice how the s on top in the original units cancels out the s on bottom from the factor of 1, leaving only min from the factor of 1.
  4. Sep 11, 2010 #3
    I still don't understand.Are you converting into minutes? I converted into minutes which is 160minutes, do I take my m/160minutes to get my final answer of m/s?
  5. Sep 11, 2010 #4


    Staff: Mentor

    You have km/h and you want m/s so you need a factor which gives you m on top and cancels out the km, and you need another factor which gives you s on top and cancels out the h. Can you figure out what those factors are?
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