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Homework Help: Physics 11 vector help ?

  1. Jan 31, 2009 #1
    Physics 11 vector help plz?

    1. The problem statement, all variables and given/known data
    A boy and a girl both swim at 1.5 m/s. they set out together to cross a river that is 50.0m across and has a current flowing south at 1.0m/s.the girl takes a heading so she'll travel straight east across the river. meanwhile, the boy maintains an eastward heading that causes him to be swept downstream while crossing.
    What is the velocity of the girl relative to the ground?
    What is the velocity of the boy relative to the ground?
    how far apart will they be when both have reached the opposite bank?

    2. Relevant equations

    3. The attempt at a solution
    idk ???
  2. jcsd
  3. Jan 31, 2009 #2


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    Homework Helper

    Re: Physics 11 vector help plz?

    Since girl travels straight across the river, the resultant of two velocities ( girl's and river's) is perpendicular to the velocity of the river.
    If R is the resultant of two vectors P and Q having an angle theta, then the angle between R and P is given by
    tan(alpha) = Qsin(theta)/[P + Qcos(theta)]. In the above problem alpha = 90 degree. Find theta and R
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