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Relative motion question

  1. Sep 28, 2016 #1
    1. The problem statement, all variables and given/known data

    1. The problem statement, all variables and given/known data
    A newspaper boy throws papers sideways onto the porches of his customers while riding his bicycle along the sidewalk. The sidewalk is 15m in front of the porches. The boy throws the papers at a horizontal speed of 6m/s relative to himself, and rides the bicycle at a speed of 4m/s relative to the sidewalk.
    Question: If he waits until he is directly opposite a porch, at what horizontal angle with respect to the sidewalk will he have to throw the paper to hit the porch?


    2. Relevant equations

    soh cah toa
    3. The attempt at a solution
    Here is the triangle I'm supposed to get, but what I don't get is why is the hypoteneuse of the triangle 6m/s, when that is the horizontal speed, shouldn't the horizontal line of the triangle be 6?

    4509cb0bc1cc061483b2f9632c47e7b5.png
     
  2. jcsd
  3. Sep 28, 2016 #2
    Who said that triangle has to be like that? I also understood from the question that 6m/s should be on the X the other side, not the hyp.
    And thus hypotenuse would be derived from pythagoras theorem
     
  4. Sep 29, 2016 #3

    haruspex

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    He is not throwing the newspaper straight sideways from himself, but back at an angle. Yet the speed relative to the boy is 6m/s, so that is 6m/s at the perceived angle. To a bystander, the paper does travel perpendicularly to the boy's path. (But at some other speed.)
     
    Last edited: Sep 29, 2016
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