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Homework Help: Maximum Velocity in projectiles

  1. Jul 12, 2011 #1
    1. The problem statement, all variables and given/known data
    A man stands on the roof of a building of height 16.6 and throws a rock with a velocity of magnitude 25.0 at an angle of 35.0 above the horizontal. You can ignore air resistance.

    Calculate the magnitude of the velocity of the rock just before it strikes the ground.

    2. Relevant equations

    y - y0 = v0y2 + 1/2 ayt2

    vy2 = v02 + 2ay(y - y0)

    3. The attempt at a solution

    I calculated that the projectile would go 10.5 meters above the building which would make the total height of 27.1m. I also calculated how much time it would be in the air - 3.74s - and then found the range - 76.6m (I didnt do all that for fun, it was to answer other parts of this question). I figured using the second equation I listed would give me the velocity of the y component.
    I get vy = 23m/s and then divided by sin(35) to get the velocity

  2. jcsd
  3. Jul 12, 2011 #2


    User Avatar

    Staff: Mentor

    The impact angle will not necessarily be the same as the launch angle, because impact is happening at a different elevation than the launch point.

    You've determined the y-component of the velocity, and you should be able to determine the x-component. Add them like you would any vector components.

    [By the way, you could also get to the answer by employing conservation of energy]
    Last edited: Jul 12, 2011
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