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Motion Diagrams (true/false)

  1. Feb 8, 2009 #1
    1. The problem statement, all variables and given/known data

    The drawings indicate the motion of a ball (moving from left to right), subject to one or more forces on various surfaces. Each circle represents the position of the ball at succeeding instants of time. The time interval between each circle is one second.

    http://img239.imageshack.us/img239/87/kinma1rs9.gif [Broken]

    Which of the following statements are true about the motions depicted in the figures above? (Give ALL correct answers: B, AC, BCD.., or None )

    The velocity of the ball in pictures C and F is decreasing
    The velocity of the ball in pictures B, C and F is constant
    The acceleration of the ball in pictures B and C is zero
    The acceleration of the ball in pictures A and F is positive
    The velocity of the ball in pictures B, C and E is increasing

    2. Relevant equations



    3. The attempt at a solution

    1. False, C looks like its moving faster.
    2. False, can't be constant, doesn't look the same at all.
    3. False, C is clearly accelerating
    4. False, A is negative
    5. False, 2 are constant


    Maybe I'm doing something wrong here? BEcause this isn't right.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 9, 2009 #2
    bump!!!!!! help!
     
  4. Feb 9, 2009 #3

    cjl

    User Avatar

    No, it isn't right. The trick in this is knowing that the shots of the positions were always taken at the same time interval. Because of this, you can tell that the velocity of ball D is increasing, because in the direction of motion, it has traveled farther in each subsequent picture. If the distance is decreasing between subsequent photos, the velocity is decreasing, and if it is constant, the velocity is constant. Also, make sure to separate velocity and direction - if the acceleration is positive, all it requires is that the velocity be increasing - it is irrelevant whether it is going up or down a hill.
     
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