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Homework Help: Projectile motion of a stone

  1. Nov 1, 2007 #1
    1. The problem statement, all variables and given/known data

    Suppose the stone is thrown at an angle of 30 degrees below the horizontal. If it strikes the ground 57m away. find (a) the time of flight (b) the initial speed, and (c) the speed and the angle of the velocity vector with respect to the horizontal at impact. (Hint: for part (a) use the equation for the x-displacement to eliminate vot from the equation for the y-displacement.)

    answers: (a) 1.57s (b) 41.9 m/s (c) 51.2 m/s, -45 degrees

    2. Relevant equations

    x final- x inital= vo cos(theta)t
    y final- y initial= vo sin(theta)t- 1/2g t^2

    3. The attempt at a solution

    i get that vot= 57/cos(30) and i plug it into the equation for y-position but i can't get the same answer.
  2. jcsd
  3. Nov 1, 2007 #2
    I'm a bit curious, what value are you using for the displacement y?
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