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Homework Help: Question on Relativity

  1. Feb 15, 2006 #1
    I have a teacher who is lacking in the explanation department, so I figured I could find an answer here. We are doing relativity in class, and I have a quick question on it.

    The problem is, "A passenger in a convertible throws a ball up into the air. the car is going 35 m/s. The upward velocity of the ball is 8 m/s. Give the equations that specify the ball position with regards to: the passenger (prime coordinates) and an observer on the road (unprime coordinates)."

    In the above problem, we are supposed to find x, y, z, x prime, y prime, and z prime. Our teacher told us that y and y prime are the same value, which I found. However, I cannot find x, x prime, z, or z prime. Any hints would be very helpful to me. The teacher said the following: x=x'+vt and x'=x-vt. However, I do not have the time, so I can't use those equations.

    Please help ASAP.
  2. jcsd
  3. Feb 15, 2006 #2


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    I think it would have taken you less time to determine the answer using those equations then to write the message.

    Do you know the kinematic equations for motion at rest? You can use those and just substitute the equations into eachother using the Gallilean transformation.
  4. Feb 15, 2006 #3
    But I can't use those equations because all I have is the two velocities. I don't have t, don't have x or x', and I don't know which v to use.
  5. Feb 15, 2006 #4


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    So when you say your teacher is "lacking in the explanation department" what you mean is you can't be bothered to do what he suggested?
  6. Feb 15, 2006 #5


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    Or even worse, did the teacher not know how to use the equations?
  7. Feb 15, 2006 #6
    No. I mean that I don't understand a thing he says. I went in for help on this problem after school. He threw the two equations x=x'+vt and x'=x-vt at me, told me to figure it out, and then I left.

    I don't get how I'm supposed to solve this problem without having t or either x value.
  8. Feb 15, 2006 #7


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    Well it appears that all he is asking for is the actual equations so you don't really need t although its pretty easy to figure out using the kinematic equations.
  9. Feb 15, 2006 #8
    But on the sheet, it has answer blanks for x', y', z', x, y, z. So I'm guessing he wants all the values. And we learned nothing about kinematic equations.
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