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Homework Help: Kinetic Energy&Work

  1. Dec 29, 2013 #1
    1. The problem statement, all variables and given/known data
    *The experiments drawing is attached.
    Ek at point O (the moment the ball is being pushed) = 1.25 J
    D (0 ; 0) , C (0 ; 0.05), E (0.25 ; 0), F (0.50 ; 0), G (0.75 ; 0)
    Friction is neglected

    1.Complete the chart by typing if the value of each variable is rising / decreasing / constant / equals to zero. (attachment added)
    2.Calculate the balls speed at point O.
    3.Calculate the work of ∑F that has been working on the ball from A to C. ( W∑F )
    4.The ball reaches one of the holes G/F/E - calculate which one it reaches.
    5.Add Cartesian axis on the drawing, locate in it the points :C,D,E,F,G and add to the drawing the route of the ball from point C until the point he touches the ground.
    6.Players has springs that pushes the spring with a constant F that is higher/lower than the original spring. Which one does one has to use for the ball to fall after point G? (The distance of AA' stays the same)

    *I'm having difficulties with basically everything*

    2. Relevant equations

    3. The attempt at a solution

    1. At point A'O: v:rising , a:rising, ∑F:constant, Mechanic Energy: rising
    At point OC: v:constant , a:0, ∑F:constant, Mechanic Energy: constant.
    From point C until the ball touches the ground: v:constant, a:rising, ∑F:rising, Mechanic Energy: constant.

    Ek=mv^2/2 => 1.25 = 0.1v^2/2 => 2.5= 0.1v^2 => v=5 m/s

    *If the question has anything missing - please write the answer you would have done just without placing the number in the variable. As in a parametric answer.

    Attached Files:

    Last edited: Dec 29, 2013
  2. jcsd
  3. Dec 29, 2013 #2


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    Seems to me there is some verbal description of the experiment missing at the start.
    Are we to ignore rolling/spin?
    As the spring expands from AA' to AO, is the force in the spring increasing, decreasing, or staying the same?
    In the chart, which energy does E refer to? Is it just the energy in the ball (PE+KE) or the energy of the whole system, or something else?
    You have calculated the velocity of the ball at O (assuming not rolling). What will be the speed at C? What dynamical equations do you know for the flight of the ball after C?
  4. Dec 29, 2013 #3
    We are to ignore the rolling/spinning.
    We assume that while the spring expands the force is staying the same.
    In the chart, E refers to Mechanic Energy (Ep+Ek).
    The speed at C should be 5 m/s,
    and the afterwards I suppose it's to be projectile motion
  5. Dec 29, 2013 #4


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    You're told that? Please post all the text describing the experiment.
    Yes, but just of the ball or of the whole system (i.e. including the spring)?
  6. Dec 29, 2013 #5
    The whole system I suppose, you think you can you help me solve it?
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