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Relative Motion Question

  1. Oct 14, 2011 #1
    1. The problem statement, all variables and given/known data

    While driving north at 25 during a rainstorm you notice that the rain makes an angle of 38 with the vertical. While driving back home moments later at the same speed but in the opposite direction, you see that the rain is falling straight down.
    a)From these observations, determine the speed of the raindrops relative to the ground.
    b)From these observations, determine the angle of the raindrops relative to the ground.


    2. Relevant equations

    V=vy+vx
    V'=VR-V

    Where VR is the velocity of the rain



    3. The attempt at a solution

    When driving north I got

    V=(-vRsinθR)i + (-vRcosθR)j

    Using

    V'=VR-V

    I get V'=VR-V(-vRsinθR-25)i + (-vRcosθR)j




    Im not sure how to set it up for going south. Any suggestions?
    Would it look like this? V'=0i+ (-vRcosθR)j
    ?
    And to find θ, would i use [ v'x / v'y}tan-1?


    I thinks mostly all the subscripts and whatnot thats messing me up.
    Thanks in advance for any help given :)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 15, 2011 #2
    Think of the three reference frames in this problem of interest. At rest relative to earth, moving away from home in the car, moving towards home in the car. In each reference frame the rain will be falling at a different angle. See,



    Good luck!
     

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