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Homework Help: Projectile on horizontal surface

  1. Aug 26, 2012 #1
    1. The problem statement, all variables and given/known data

    A particle is projected with a speed of 98 m s−1 at an angle A to the horizontal.
    The range of the particle is 940·8 m. Find
    (i) the two values of A

    3. The attempt at a solution

    U = 98cosAi + 98sinAj

    i direction

    s = ut
    940.8 = 98cosAt

    j direction

    s = ut + (0.5)at[itex]^{2}[/itex]
    0= 98sinAt - (0.5)gt[itex]^{2}[/itex]
    98sinA = gt/2
    t = 20sinA

    i direction
    940.8 = (20sinA)(98cosA)
    94.8 = (2sinAcosA)g
    94.8 / g = sin2A



    And I end up with a math error. Help please.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Aug 26, 2012 #2

    TSny

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    Oops.
     
  4. Aug 26, 2012 #3
    Ooops, sadly it doesn't solve the problem.

    94.08 = 2sinAcosA(9.8)
    94.08 / 9.8 = sin2A
    9.6 = sin2A

    math error
     
  5. Aug 26, 2012 #4

    TSny

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    This equation doesn't follow from 940.8 = (20)sinAcosA(98)
     
  6. Aug 26, 2012 #5
    AHHH!! Stupid error!! Thanks!!
     
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