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Homework Help: Grade 10 Physics: Velocity

  1. Mar 9, 2009 #1
    1. The problem statement, all variables and given/known data
    A flying saucer decelerates uniformly from 20 m/s [E] to 50 m/s [W] in 9 seconds. Find the velocity for the 9.0 interval.

    2. Relevant equations
    Velocity = acceleration x time
    or Velocity = displacement/time

    3. The attempt at a solution
    Velocity1 = 20 m/s [E]
    Velocity2 = 50 m/s [W]
    Time = 9 s
    Velocity = 30 x 9
    = 270

    However, the answer should be 15 m/s [W].
  2. jcsd
  3. Mar 9, 2009 #2


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    Homework Helper

    You need to consider what velocity represents.

    V = Δx/Δt

    Your space ship has been traveling East at 20m/s and reverses to 50m/s West.

    First figure how far it went in stopping going East and then figure how far it went West. Then you can develop the Δx that it traveled in the 9 sec.

    The units of your attempt should have told you there was a problem, because you had just the units of displacement in your answer.
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