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Homework Help: Projectile Motion - motion on a horizontal surface !

  1. Jan 5, 2013 #1
    Projectile Motion - motion on a horizontal surface plz help!

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

    Isaac Newton shot a dirty snowball 76m across a horizontal field. It passed directly over Edmund Haley's head, and was in the air for 7.6s. How high did it get above the field? Answer in m.

    2. Relevant equations

    Δd = V1(Δt) + 1/2(g)(Δt)^2
    and i think some projectile motion equations, not sure if those will help.

    3. The attempt at a solution

    since at maximum height the velocity will be zero i tried this:
    Δd = 0m/s(Δt) - 1/2(9.8m/s^2)(7.6s)^2
    Δd = 283m
    but this is not the right answer, so i would appreciate it if someone could help me with this.
    Thank you.
  2. jcsd
  3. Jan 5, 2013 #2
    Re: Projectile Motion - motion on a horizontal surface plz help!

    Hi bonbloc
    At maximum height, velocity (its vertical component, that is) is 0
    By symmetry, you can easily see that the maximum height is also reached right in the middle of the trajectory.
    So you will have v=0 at T/2 (7.6/2)
    From this, you should be able to calculate the vertical component of the velocity.
    Write then the equation of motion y(t) which will require this initial value and plug in the found velocity and T/2

  4. Jan 5, 2013 #3

    rude man

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    Re: Projectile Motion - motion on a horizontal surface plz help!

    Think of the snowball at its high point. It took 7.6/2 = 3.8s to get there (symmetrical trajectory). Now it's stationary & beginning to fall. How far does it fall in the remaining 3.8 sec?

    It doesn't matter how far it went horizontally, or what its horizontal velocity was.
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