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Homework Help: Projectile Motion problem.

  1. Sep 17, 2008 #1
    1. The problem statement, all variables and given/known data
    I have a test on Projectile motion tomorrow, and I am just trying to figure out as much as I can about these kind of problems before that.

    circus performer is shot out of a cannon and flies over a net that is placed horizontally 5.0 m from the cannon. When the cannon is aimed at an angle of 30° above the horizontal, the performer is moving in the horizontal direction and just barely clears the net as he passes over it.

    (a) What is the muzzle speed of the cannon?
    (b) How high is the net?

    2. Relevant equations

    Vy= Voy + at

    i think thats it.

    3. The attempt at a solution

    Okay, so i tried...

    v= d/t
    Vo cos(30) = 5/t
    Vo(.866)= 5/t
    Vo(4.330) = t

    Then I think I use Vy= Voy +at, but I dont know what to do, do I just use it like Vy= Vo sin(30) + (-9.8)(Vo(4.330))?

    My biggest problem is that I don't know the steps in solving the problems, all my teacher has said to me is that I have to soolve for time and go from there.

    Any help is appreciated.
  2. jcsd
  3. Sep 17, 2008 #2


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    There's another equation you can use y(t)=v0y*t-(1/2)*g*t^2. Does that help?
  4. Sep 17, 2008 #3
    not really, but ill keep that in mind, My real problem is I don't understand when a certain variable is 0 or not.
  5. Sep 17, 2008 #4


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    That's kind of vague. And I've realized I jumped the gun on thinking you had t in terms of Vo. You had Vo(.866)= 5/t. You didn't solve for t correctly. Can you try that again?
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