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Projectile motion problem

  1. Sep 9, 2012 #1
    1. The problem statement, all variables and given/known data

    starting at 2.00m away from a waterfall .55m in height, at what minimum speed must a salmon jumping at an angle of 32.0° leave the water to continue upstream?

    2. Relevant equations

    Δx=vi(cosθ)Δt
    Δy=vi(sinθ)Δt-1/2g(Δt)2

    3. The attempt at a solution

    there were some other equations in the book, but i just can't make the connection, i know i can find vx,i and vy,i if i had vi but i don't know any velocities. i tried using cos32°=(2.0m/h) but i can't get any further, so little help would be appreciated. also i am new.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 9, 2012 #2
    From the first equation, you can express Δt (unknown) in terms of everything else in it.

    You can plug that Δt into the second equation, thus getting an equation for the unknown initial speed.
     
  4. Sep 9, 2012 #3
    starting at 2.00m away from a waterfall .55m in height, at what minimum speed must a salmon jumping at an angle of 32.0° leave the water to continue upstream?
    ....................................................

    First you have to know about vector operation.
    [itex]\vec{A}[/itex]=[itex]\vec{B}[/itex]+[itex]\vec{C}[/itex]

    You have to think of the reversal.
    The salmon is jumping at minimum speed with 32.0° angle.
    So will call this velocity [itex]\vec{A}[/itex]

    Thus [itex]\vec{A}[/itex] has 2 components [itex]\vec{B}[/itex] which say in forward direction and [itex]\vec{C}[/itex] in upward direction.

    Horizontal velocity is constant.
    Vertical motion is affected by gravity.
     
    Last edited: Sep 9, 2012
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