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Homework Help: Motion and Speed

  1. Jan 10, 2010 #1
    1. The problem statement, all variables and given/known data
    Three identical balls, all with the same initial speed, are thrown by a juggling clown on a tightrope. The first ball is thrown horizontally, the second is thrown at some angle above the horizontal, and the third is thrown at some angle below the horizontal. Disregarding air resistance, describe the motions of the three balls, and compare the speeds of the balls as they reach the ground.

    2. Relevant equations

    3. The attempt at a solution
    I know that when the balls are thrown no matter their position, they will all land at the same time, but im not sure about the speeds
  2. jcsd
  3. Jan 10, 2010 #2
    I'm not sure if I agree with you.

    If the clown were to throw a ball at an angle below the horizontal (going towards the ground) and another ball going vertically up they aren't going to hit the ground at the same time.
  4. Jan 10, 2010 #3
    the balls thrown vertically and horizontally will land at the same time though right?
  5. Jan 10, 2010 #4
    How would you figure that?

    I can already tell you the answer is no, but more importantly we need to correct this flaw in your reasoning.
  6. Jan 10, 2010 #5
    we did an experiment in my class when you throw a ball directly vertical and a ball horizontally they land on the ground at the same time, but with the balls being thrown above and below the horizontal i suppose the results would be different
  7. Jan 10, 2010 #6


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    I think you mean, when a ball is DROPPED vertically and thrown horizontally, they land at the same time. If you actually throw a ball UP vertically, then it's not going to land at the same time as a ball thrown horizontally. (Just think, if you threw that ball really really hard, it'd take a while for it to come down right?)
  8. Jan 10, 2010 #7
    If you threw a ball horizontally it would have no component of vertical velocity and begin falling towards the ground with an acceleration of g immediately upon release.

    If you threw a ball directly upwards it would have some vertical velocity going upwards, so until this velocity is reduced to 0 it will continue to move in the upwards direction. Then, after it reaches its maximum height will it fall towards the ground with an acceleration of g.

    Got it?
  9. Jan 10, 2010 #8
    yes that is what we did, my mistake.

    yes i now understand. thank you both very much
  10. Jan 10, 2010 #9
    Hahaha sarah i randomly found you on the internet
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