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Question wording- incline question

  1. Nov 8, 2009 #1
    The question was:

    A 4.5-kg mass is given an initial velocity of 14 m/s up an incline that makes an angle of 37o with the horizontal. When its displacement is 8.0 m, its upward velocity has diminished to 5.2 m/s.

    I'm confused with directions of the velocity. In the solution they used the equation

    vf2=vi2+2*a*d

    anyway to find 'a' they subtracted (142-5.22)/(2*8)

    So doesn't this mean initial velocity and the upward velocity are parallel since they are being subtracted. I assumed the initial velocity would be parallel to the incline and the upward velocity completely vertical and thus i would have to 5.2/sin37.

    When you read the question, what direction would you assume? Maybe it's right and i'm just mixing up the axis?
     
  2. jcsd
  3. Nov 8, 2009 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Why would you assume the upward velocity was "completely vertical"? If the object were moving vertically, there would be no reason to mention the incline! The object is moving up the inclined plane. Yes, its velocity is always parallel to the incline.
     
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