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Homework Help: Weird wording, can't understand what they want

  1. Sep 16, 2013 #1
    1. The problem statement, all variables and given/known data
    Figure P4.31 represents the total acceleration of a particle
    moving clockwise in a circle of radius 2.50 m at a certain
    instant of time. At this instant, find (a) the radial acceleration,
    (b) the speed of the particle, and (c) its tangential

    2. Relevant equations

    3. The attempt at a solution
    I probably don't need help with the problem per se. I just need help understanding what they want from me. What in god's name do they mean with "represents the total acceleration"!? The figure is just a circle that shows the radius, an angle, the velocity vector and an acceleration vector that is not centripetal. Oh yeah, and it says a=15m/s^2
  2. jcsd
  3. Sep 16, 2013 #2
    Total acceleration is the acceleration vector you are given. You are given its magnitude and, apparently, its angle with the velocity vector.
  4. Sep 16, 2013 #3
    http://www.csupomona.edu/~skboddeker/131/131hw/ch4h.htm [Broken]
    It's 4.5 on there.

    Thanks Voko!

    I'm still sort of confused... If there is another acceleration aside from the centripetal, then the object wouldn't be traveling in a circular path at all. Wouldn't it actually be moving further away from the center in this case?

    Also, when I draw the resultant vector, how do I know if I'm supposed to draw it from from the centripetal acceleration to the total acceleration or vice versa, or does it not matter and why?
    Last edited by a moderator: May 6, 2017
  5. Sep 16, 2013 #4
    As shown in the diagram, total acceleration is the vector sum of radial acceleration and tangential acceleration.

    It is perfectly possible to have non-zero tangential acceleration in circular motion. Consider a wheel initially at rest. Then at some point it is spinning with some constant speed. Clearly it must have had tangential acceleration between these two states. Yet all of its points can only move circularly.
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