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Homework Help: Kinematics question needed to be solved. Help please

  1. Oct 15, 2011 #1
    1. The problem statement, all variables and given/known data

    A basketball is being thrown at the hoop (3.0m high) from 4.0 meters away. If the initial height of the ball is at 1.5m with an initial velocity of 3.0 m/s, at what angle should the ball be thrown? (Assume that air resistance is zero, and gravity = 9.81 m/s^2)

    2. Relevant equations

    This is a kinematics problem. Even my teacher has trouble solving it. Please help. The main formulas are:

    xf = x0 + Vx t + 1/2 a t^2

    yf = y0 + Vy t + 1/2 a t^2

    3. The attempt at a solution

    By using the above two formulas, we came up with a quadratic equation involving tan() and cos() functions. We can't go further. Anyone suggestions?

    12 tan(x) - 8.72(1/cos(x))^2 = 1.5

    Let x be the starting angle of the ball being being thrown (above the horizontal)

    Note: you can't just throw the ball to the hoop in a straight line, you will hit the hoop instead.
    Last edited: Oct 15, 2011
  2. jcsd
  3. Oct 15, 2011 #2
    if you show how you got the equation someone can help you.
  4. Oct 15, 2011 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to Physics Forums.

    Okay, but a would be zero in the xf equation.

    I get almost the same thing, except that I have 4tan(x) instead of 12tan(x).

    It's probably easiest to use a graphing calculator to solve the equation at this point. You only need to consider x between 0° and 90°, of course.
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