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Homework Help: Help on projectile motion

  1. Feb 24, 2009 #1
    I have two problems that I need help on.

    1. The problem statement, all variables and given/known data
    For the circus, they show a demonstration of projectile motion that usually warrants applause from the audience. At the instant a dart is launched at a high velocity, a target (often a cardboard money) drops from a suspended position downrange from the launching device. Show that if the dart is aimed directly at the target, it will always strike the falling target. (Use a specific set of numbers). So yeah, you're not given anything.

    2. Relevant equations
    No idea what equations you need.

    3. The attempt at a solution
    No idea on what to do.

    1. The problem statement, all variables and given/known data
    A child throws a ball onto the roof of a house, then catches it with a baseball glove 1 m above the grown. The ball leaves the roof with a speed of 3.2 m/s.
    a) For how long is the ball airborne after leaving the roof?
    b) What is the horizontal distance from the glove to the edge of the roof?
    c) What is the velocity of the ball just before it lands in the glove.

    Two details that weren't given to you is that the angle is 33 above the horizontal. However, because the ball is rolling DOWN on the roof, the angle, and the whole diagram is flipped around. Also, as the ball leaves the roof, it drops 5.2 m before it is caught.

    2. Relevant equations
    These equations may be of use:
    X = (vi^2sin2FETA)/g
    T = ((2vi)sinFETA)/g

    3. The attempt at a solution
    What I did is that I used SOH to find DELTA Y, then I subbed in everything to DELTA Y = (viy)(DELTA T) - 1/2gDELTA T^2. Then I used the quadratic formula to find T, but I kept getting a math error.

  2. jcsd
  3. Feb 24, 2009 #2


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    Homework Helper

    For the Circus, aren't the bullet and the target both dropping with the same acceleration? Then doesn't that mean that the horizontal velocity, so long as it is fast enough to get there before the ground interrupts the act, will continuously close the distance until impact. (If you were in the frame of reference of the object all you would see is the bullet coming straight at you.)

    For 2) what is the component of vertical velocity?

    Why don't you fill in your equation with the numbers you used?
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