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Homework Help: Elimination on velocities and angles

  1. Jan 29, 2009 #1
    1. The problem statement, all variables and given/known data

    How do you eliminate this?

    V3(cos A) + V4(cos 30) = 5 Equation 1
    V3(sin A) = -(V4)(sin 30) Equation 2
    V3^2 + V4^2 = 25 Equation 3

    2. Relevant equations

    3. The attempt at a solution

    I let

    x= V3 ; y=V4

    and I got

    x(cos A) + y ((sqrt)3) = 10
    -2x(sin A) = y
    x^2 + y^2 = 25

    but I'm totally stuck... any help?
  2. jcsd
  3. Jan 29, 2009 #2
    Replace value of V4 from 2 in 1 and 3,

    Square equation 1 to get expression for angle A,

    Replace value of angle A in eq 3 to get value of V3
  4. Jan 29, 2009 #3


    User Avatar
    Science Advisor
    Homework Helper

    Two methods:

    i] put x = 5cosB, y = 5sinB

    or ii], in this particular case, it seems easier to use the second equation to eliminate y immediately. :wink:
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