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Determine the time it takes for the ball to reach the plane of the fence

  1. Nov 24, 2003 #1
    Thanks for any help in advance.
    A ball of mass 0.5 kg, initially at rest, is kicked directly towards a fence from a point 32 meters away. The velocity of the ball as it leaves the kicker's foot is 20 meters per second at an angle of 37 degrees above the horizontal. The top of the fence is 2.5 meteres high. The kicker's foot is in contact with the ball for 0.05 second. The ball hits nothing while in flight and air resistance is negligible.

    a) Determine the magnitude of the average net force exerted on the ball during the kick.

    b) Determine the time it takes for the ball to reach the plane of the fence.

    c) Will the ball hit the fence? If so, how far below the top of the fence will it hit? If not, how far above the top of the fence will it pass?

    A 5.0 kg monkey hangs initially at rest from two vines A and B. Each of the vines has a length of 10 meters and negligible mass. Vine A is 30 degrees above horizontal then a 90 degree angle, and 60 degree of vine B.

    a) Determine the tension in vine B while the monkey is at rest.

    The monkey releases vine A and swings on vine B. Neglect air resistance.

    b) Determine the speed of the monkey as it passes through the lowest point of its swing.

    c) Determine the tension in vine B as the monkey passes through the lowest point of its first swing.

    http://ljhs.sdcs.k12.ca.us/faculty/mteachworth/physics-folder/units/ap-practice-problems-html/vert-circle-n-proj/ap-vertical-circle-n-proj.html [Broken]
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Nov 24, 2003 #2


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    Science Advisor

    These are relatively straight-forward applications of the basic formulas connecting acceleration, velocity, and distance. Show us what you have done so far and where you are stuck.
  4. Dec 2, 2003 #3
    I try my best to offer some assistance

    part A is simply a problem dealing with impulse. We know that momentum=mass*velocity and that a change in mometum = impulse.

    The momentum of this ball is (20 m/s) * 0.5 kg = 10 kg * m/s

    Impulse = force * time

    Ft = mv
    Ft = 10
    F(0.05) = 10
    F = 200 newtons

    Part B)

    time = distance/velocity

    time = 32 m / horizontal velocity
    time = 32 m / ((cos 37) * 20) m/s
    time = 32 m / ((4/5) * 20) m/s
    time = 2 seconds

    c) d = vt + .5at^2

    plug in your values for that, with a being -9.8 m/s^2 to get d
    if d is greater than 2.5 m, then the ball has crossed the fence
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