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Homework Help: A Coordinates and Interval Question

  1. Jan 15, 2010 #1
    1. The problem statement, all variables and given/known data
    During a 4.95 s interval, a particle's coordinates change from x = 10.4 m, y = 4.95 m to x = 31.5 m, y = -4.95 m. Assuming the particle's velocity is constant, what will its coordinates be at the end of the next 4.95 s interval?

    x= ____m
    y= ____m

    2. Relevant equations

    3. The attempt at a solution
    My first thought was to take the x and y's given and find y=mx+b however I'm not sure that it is relevant or even helpful.

  2. jcsd
  3. Jan 15, 2010 #2


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    Science Advisor
    Homework Helper

    You should consider both directions independently.

    So x and y satisfy
    x = u t + a,
    y = v t + b

    Equivalently, the distance covered in the second 4.95 seconds is the same as that covered in the first interval.
  4. Jan 15, 2010 #3

    I'm not sure I understand what you're saying. What do the variables represent in your equations? I'm sorry if these are silly questions, however I just finished my second day of Physics and am completely new to it (and also very bad at it!).
  5. Jan 15, 2010 #4


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    Staff: Mentor

    CompuChip is showing the equations of motion for a constant velocity. You can break the problem up into the orthogonal velocities in the x and y directions. So his first equation says that x(t) is equal to x(0) = a, plus an offset given by the velocity u multiplied by the time t.

    Does that help?
  6. Jan 15, 2010 #5

    I understand that much, however I don't understand how those equations work with my numbers?
  7. Jan 15, 2010 #6


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    Staff: Mentor

    You are given a delta-t and a delta-x and a delta-y. From those numbers and those equations, you can figure out what those constants are (u, a, v, b). With those constants and the next delta-t, you can figure out what the final positions will be after the second delta-t.
  8. Jan 15, 2010 #7
    Thank you, I appreciate your time!
  9. Jan 15, 2010 #8
    I definitely over analyzed the question. All you do is find the change in x and changed in y and add them to the last x and y coordinates. I didn't have to do anything with time or velocity.
  10. Jan 15, 2010 #9
    In this case, yes, but what if the next interval was 6.1 seconds. Profs have bbeen known to do such things, esp physics profs!:smile:

    So knowing the velocities is a necessary skill on the third day.
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