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Kinematics Question

  1. Sep 9, 2007 #1
    Kinematics Question (Speed, velocity and acceleration)

    1. The problem statement, all variables and given/known data
    For each of the following situations below circle the appropriate signs for each quantity listed.
    Assume east is + and west is -

    (see photo below)

    2. Relevant equations
    None I believe

    3. The attempt at a solution
    I did it but I'm not really sure if I'm right. Can someone tell me if its all right or how you determine the right answers
    Last edited: Sep 9, 2007
  2. jcsd
  3. Sep 9, 2007 #2

    Doc Al

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    Staff: Mentor

    Only b is correct. Explain your reasoning for your answers. For example, what determines whether displacement is + or -?
  4. Sep 9, 2007 #3
    Well to be honest I'm really not sure. This is my first week of Physics (AP) and I've been really confused about the class so far.

    For A and C which parts were wrong?

    For A:
    Displacement + because as you move away from 0 your displacement from the original increases doesn't it?
    Velocity + because your moving west so its +
    Acceleration your speeding up so its +
    If you start east and move west isn't it then negative?

    I'm really not sure. If you can could you please explain the right answers to me it would be a huge help
  5. Sep 9, 2007 #4

    Doc Al

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    Staff: Mentor

    Signs--which indicate direction--count. Note the instructions that east is + and west is -. If it is east of the origin, its displacement is +.

    Again, direction and signs count.

    Speeding up in what direction?
    Isn't what negative? "Moving west" describes velocity, so velocity would be negative. But what about displacement and acceleration?
  6. Sep 9, 2007 #5
    Ok then for A taking direction into account since west is - then displacement, velocity and acceleration would all be - wouldn't they?

    For C acceleration would be + and displacement + because your position is changing.

    Is that correct?
  7. Sep 9, 2007 #6

    Doc Al

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    Staff: Mentor

    All good!
  8. Sep 9, 2007 #7
    Thank you very much
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