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Momentum Principle. Please help (due in 1 hour 30 minutes)

  1. Sep 2, 2011 #1
    1. The problem statement, all variables and given/known data

    Part 1:

    EDIT: I got part 1. The answers is 11.1m/s can anyone still help me with the others? I got 11.1 by this formula: Vi-(9.8*t)

    A ball is kicked from a location on the ground
    ~ri = <10, 0,−8>m with initial velocity
    ~vi = <−10, 16,−5> m/s.
    The ball’s speed is low enough that air resistance is negligible.
    Find the y component of the ball’s velocity
    0.5 s after being kicked. (Use the Momentum
    Principle!)
    Answer in units of m/s

    2. In this situation (constant force), which velocity will give the most accurate value for
    the location of the ball 0.5 s after it is kicked?
    1. The final velocity of the ball
    2. The initial velocity of the ball
    3. The arithmetic mean of the initial and
    final velocities

    3. What is the y component of the average velocity (vector) of the ball over this time interval?
    Start by finding Vavg,y.
    Answer in units of m/s

    4. Now use the average velocity to find the y
    component of the ball’s position 0.5 s after
    being kicked.
    Answer in units of m

    5. Now consider a different time interval: the interval between the initial kick and the moment when the ball reaches its highest point. We want to find how long it takes for the ball to reach this point, and how high the ball
    goes.

    What is the y component of the ball’s velocity at the instant when the ball reaches its
    highest point (the end of this time interval)?
    Answer in units of m/s

    6. Consider the expression for the update form
    of the momentum principle,
    mvf,y = mvi,y + Fnet,y delta(t).
    If you were to simplify this expression and
    fill in all known quantities with numerical
    values, what would you end up with? (Here,
    vf,y refers to the y component of the ball’s
    velocity at the highest point in its trajectory.)
    1. 11.1 m/s = 16 m/s+(−9.8 m/s2) (0.5 s)
    2. 0 = 11.1 m/s + (−9.8 m/s2)delta(t)
    3. 0 = 16 m/s + (−9.8 m/s2) (0.5 s)
    4. 0 = 16 m/s + (−9.8 m/s2)delta(t)
    5. 11.1 m/s = 16 m/s + (−9.8 m/s2)delta(t)

    7. How long does it take for the ball to reach its highest point?
    Answer in units of s

    8. Knowing the time you calculated in the previous parts, first find the y component of the
    average velocity during this time interval, and then use it to find the maximum height attained by the ball.
    Answer in units of m

    2. Relevant equations

    p=gamma(m)(v)

    Momentum Principle
    Pf=Pi +Fnet(delta(T))

    3. The attempt at a solution

    I tried using the momentum principle but I don't know where to get the final velocity from.

    Any help is appreciate. I can't seem to figure out how to do this multiple question problem. It is due in about a 1 hour and 30 minutes. So please help me out if you know anyway to figure out how to do this.
     
    Last edited: Sep 2, 2011
  2. jcsd
  3. Sep 2, 2011 #2
    EDIT: I got part 1. The answers is 11.1m/s can anyone still help me with the others? I got 11.1 by this formula: Vi-(9.8*t)
     
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