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Homework Help: 1d Motion

  1. Sep 17, 2005 #1
    2d Motion

    I've been stuck with this problem for a while. Appreciate if anyone can point me in the right direction.

    A boy stands in a field, he throws a stone with an initial 45 degree angle. The field has a 5 degree angle downwards, so the stone touches down at -5 degree angle and 82 meters away. g=9,8m/s^2

    Find the time (t) for the entire throw, and the initial velocity (v0) for the stone.
     
    Last edited: Sep 17, 2005
  2. jcsd
  3. Sep 17, 2005 #2
    sin45*v0*t=82*cos50
    sin45*v0=g*t1
    2*t1+t2=t
    sin45*v0*t2+0.5*g*t2^2=82*sin50

    4 equations for 4 unknows

    we use the symmetry of the motion, and the independence of the motions in different directions
     
  4. Sep 17, 2005 #3
    sorry, cos50 and sin50 above mean cos5 and sin5
     
  5. Sep 17, 2005 #4
    and you can also use energy , but i don't think it woulb be much more easier
     
  6. Sep 17, 2005 #5
    couldn't i do: R=Vi^2*sin2(THETAi)/g

    R=the length of the throw

    Solving for Vi= 21.72 m/s
     
  7. Sep 18, 2005 #6
    And then set up an integral for time?
     
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