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Homework Help: Free Fall

  1. Feb 2, 2005 #1
    Suppose I throw an object up in the air. What is the direction of velocity on the way up, at its highest point and on the way down. Accelartion is constant, correct?
  2. jcsd
  3. Feb 2, 2005 #2
    Velocity is just speed but with a direction. As the object goes up, the velocity will be in the same direction as the object travels (up, which is +ve). At the highest point, the object is not moving. And on the way down, the object is moving down, so you can figure the velocity, right?

    As for acceleration, it is ALWAYS equal to [tex]-9.81\frac{m}{s^2}[/tex]
  4. Feb 2, 2005 #3
    Sorry this is childs play but I am new to physics. So velocity is positive as it goes upward, when it reaches the top it becomes zero, and as it falls velocity is negative.

    Suppose i throw an object upward at 5m/s when the object returns to my hand its velocity is still 5m/s, correct? Or wait -5m/s?
  5. Feb 2, 2005 #4


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    Yes,once u chose an axis for the vertical coordinate,then u have various signs for the components of the vectors,in particular for "v"...

    So it's -5ms^{-1}.

  6. Feb 2, 2005 #5
    Anytime an object is moving upwards, its velocity is +ve. Anytime it's moving downwards, its velocity is -ve. If it's not moving, its velocity is zero. So when the object returns to you hand, its velocity is -5m/s. (Same speed as when it left your hand, but opposite direction). Hope you get it now... :smile:
  7. Feb 2, 2005 #6
    This is only true if you define the upwards direction as positive.
  8. Feb 2, 2005 #7
    Yes, Sirus. Everything is relative. But usually, when you are asked for the velocity of an object travelling downwards, you put down a negative velocity as the answer. :devil:
  9. Feb 2, 2005 #8
    wow, thats a fast response. I got it now. Thanks everyone :biggrin:
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