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Determine the balls initial velocity

  1. Dec 13, 2009 #1
    1. The problem statement, all variables and given/known data

    Question Reads: " A passenger in a hot air balloon throws a ball with an innitial unknown velocity. the ball accelerates at 9.8m/s down for 2.0s. at which time its instantenous velocity is 24m/s [45 below the horizontal]. determine the balls innital velocity "

    2. Relevant equations

    vf = vi + at

    3. The attempt at a solution

    ok, these kinds of problems are very new to me.
    i made vf = 24sine45 since we are only discussing the y direction speed.
    and vi = visinetheta.

    but the answer says 17m/s [10 degress above horizontal]

    where did 17 come from along with the angle ? please guide me
  2. jcsd
  3. Dec 13, 2009 #2
    Re: kinematics

    How it can gain horizontal velocity component if g only acts in y direction?

    So, horizontal speed is contant. The speed at 2 second = speed at 0 second.

    Now, you know after two seconds v_y is 24sine45, what it was 2 seconds?
  4. Dec 13, 2009 #3


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    Homework Helper

    Re: kinematics

    It is a projectile motion. Let initial component of velocity along y by viy. Final velocity is given. find vfy. Then use the relevant equation to find viy. Cake care of the signs of the quantities.
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