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Homework Help: Help on projectile motion problems ?

  1. May 23, 2010 #1
    Help on projectile motion problems plz?

    Someone who is 1.6m tall throws a ball 41 deg above the horizontal at 9.4m/s.

    A) How far away from the person will the ball land?
    B) How long will it be in the air?
    C) What is the ball's maximum height?

    df = di + vi(t) + .5(a)(t^2)

    Velocity of the ball in the y = 9.4(sin41) = 6.167m/s
    Time: 0 = 6.167 + (-9.8)(t); t = 0.63s
    Max vertical distance = 0 + (6.167)(.63) + .5(9.8)(.63^2) = 5.83002

    Is this right? I don't know if I did any of that right, and I don't know how to do the rest of the problem.
    Last edited: May 23, 2010
  2. jcsd
  3. May 23, 2010 #2
    Re: Help on projectile motion problems plz?

    You're well on your way now. You've figured that given an initial y-velocity, it would be smart to consider when it reaches zero velocity due to the downwards acceleration from gravity, and you've got that right. You've also calculated the max height of the ball, only forgetting the height of the thrower.

    Ask yourself now, how long does it take for the ball to drop to the ground from that height?
  4. May 23, 2010 #3
    Re: Help on projectile motion problems plz?

    Thanks! This helped a lot. I think I'll be okay from here.... just have to be able to do this on my final exam tomorrow. *Gulp* lol
  5. May 23, 2010 #4
    Re: Help on projectile motion problems plz?

    Best of luck! :)
  6. May 24, 2010 #5
    Re: Help on projectile motion problems plz?

    I believe the initial height of the ball is 1.6 meters not 0

    "Max vertical distance = 0 + (6.167)(.63) + .5(9.8)(.63^2) = 5.83002"

    [PLAIN]http://img694.imageshack.us/img694/563/1111am.png [Broken]

    "Time: 0 = 6.167 + (-9.8)(t); t = 0.63s"

    the equation will only get you t1, theres still another t1 and t2 you also have to find

    you can find t2 using the equation

    x = xo + vot + (1/2)at2

    and then using the "quadratic formula"

    thus you get the time it takes to fall, and you can use that with one of the kinematic equations to get the horizontal distance traveled and how long it will be in the air.
    Last edited by a moderator: May 4, 2017
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