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Question on relative motion and circular motion.

  1. Sep 10, 2006 #1
    Hey guys, I've been working on this physics for a few hours, and feel like I am just missing a key point. At first I felt that the problem was missing data, until in the same section I found another that I felt the same. Now I feel like I'm missing a concept or two.

    The first problem I have having issues with is:

    A science student is riding on a flatcar of a train traveling along a straight horizontal track at a constant speed of 10.5 m/s. The student throws a ball into the air along a path that he judges to make an initial angle of 60.0° with the horizontal and to be in line with the track. The student's professor, who is standing on the ground nearby, observes the ball to rise vertically. How high does she see the ball rise?

    Now, I see that the train is moving at 10.5 m/s, so although the student throws the ball at the angle of 60.0 degrees to the horizontal, the professor see's the ball's velocity as 10.0 m/s + the vector components at which the student throws the ball? Please guide me in the right direction.

    As for my second problem:

    A race car starts from rest on a circular track. The car increases its speed at a constant rate at as it goes 7.75 times around the track. Find the angle that the total acceleration of the car makes with the radius connecting the center of the track and the car at the moment the car completes its trip of 7.75 times around the circle.

    As for this problem, I am almost at an utter loss. Any help would be greatly appreciated, and I am by no means trying to get answers, just a general push in the right direction. Thanks in advance for your time.
  2. jcsd
  3. Sep 10, 2006 #2
    Heh, just an update, finally figured out the first one :). ANy help with the second would be appreciated!
  4. Sep 11, 2006 #3
    anyone :frown:
  5. Sep 11, 2006 #4

    Doc Al

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    Staff: Mentor

    In general, something going in a circle could have both a tangential and radial component of acceleration. However, since you are given no information about the speed of the car or the radius of the track, I don't see how you can solve this one.
  6. Sep 11, 2006 #5
    alright, thanks. In the book there was a similar problem, that asked what's the angle if it goes around once, and they said tan(1/4pi) = 4.55° is the answer. Definitely confused on this one..
  7. Sep 11, 2006 #6

    Doc Al

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    Staff: Mentor

    That answer would make sense if the car made it around in one second. Without that additional information, the problem cannot be solved.

    Are you sure you are presenting these problems exactly as given?
  8. Sep 12, 2006 #7
    Yeah I am, That's compied an pasted from webassign
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