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Homework Help: Velocity and aceleration relative

  1. Mar 2, 2010 #1
    Hello Everybody...

    i have some problems to start with this problem someone can help me?
    thanks


    in the figure, block A moves to the left with a speed of 1m / s, decreasing at a rate of 0.5 m/s2 and block C is fixed. determine the velocity of B relative to A and the acceleration of B relative to A

    [URL]http://s3.amazonaws.com/answer-board-image/201032182236340315092363625008696.jpg
     
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Mar 2, 2010 #2
    Consider this.

    Imagine the distance between the pulley and Block C is 1 meter. The distance of the rope is 2 meters since it travels "down and back" from Block C.

    So, now lets move the pulley 2 meters away from Block C. Now the rope travels down 2 meters to the pulley and back 2 meters from Block C. This is a total of 4 meters of rope.

    So, now lets move the pulley 3 meters away from Block C. Now the rope travels down 3 meters to the pulley and back 3 meters from Block C. This is a total of 6 meters of rope.

    This pattern shows that

    for whatever distance the pulley moves, its passes though twice as much rope.

    Therefore, since the pulley is connected to Block A and the end of the rope is connected to Block B, we can say that Block B moves twice as fast as Block A.
     
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