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Physics displacement velocity mass elastic/inelastic help!

  1. May 2, 2016 #1
    NO TEMPLATE BECAUSE THREAD WAS STARTED IN WRONG FORUM

    A wrecking ball is a heavy steel ball, usually hung from a crane that is used for demolishing large buildings. Suppose we had a crane with a wrecking ball with a mass of m1 = 12,000 lbs. The crane produces a displacement on the ball of a height of Δy = 8.25 meters. As the crane stops turning, the wrecking ball swings downward in a circular motion. The operator of the crane was not paying any attention as he produced a displacement on the ball and at the bottom of the swing the ball collides with a parked vehicle that has a mass of m2.
    a. At the bottom of the swing, what is the wrecking balls velocity?
    b. Suppose when the wrecking ball swings down, its collision with the parked vehicle is perfectly elastic and the wrecking ball and the parked vehicle both experience the same velocity but in different directions. What is the mass m2 of the parked vehicle?
    c. Assume the collision is perfectly inelastic and the wrecking ball and parked vehicle stay stuck together. What is the velocity of the two objects immediately after they collide?
    d. Assuming with the same condition as in part (c.), what is the wrecking ball and parked vehicles new displacement Δy? (what is its maximum height hf of the two objects)
     
    Last edited by a moderator: May 2, 2016
  2. jcsd
  3. May 2, 2016 #2
    one can calculate the velocity of the ball by using energy conservation.i.e. the potential energy must have converted to kinetic energy.
    for b....one can use conservation of momentum as well as energy as the collision is elastic.and calculate the mass
    for c again you can use momentum conservation to get velocity and can calculate height.
     
  4. May 3, 2016 #3

    haruspex

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    I assume this was moved to a homework forum by a moderator. As a result, it is in a homework forum without including any attempt at a solution, which is against forum rules. @Jphil, please supply an attempt. At the very least, mention what physical principles and equations you consider relevant.
     
  5. May 3, 2016 #4
    i used mgh=0.5mv^2 for part a and got 12.7 m/s ^2 for the answer im not sure if that was right . and then i was stuck for the rest of the attempts
     
  6. May 3, 2016 #5

    haruspex

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    I confirm your answer for part a.
    For part b, what do you think the question means by "both experience the same velocity"?
    What equations or principles do you know relating to elastic collisions?
     
  7. May 3, 2016 #6
    i think that elastic collision most of the velocity becomes transferred to the object?
     
  8. May 3, 2016 #7

    haruspex

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    No,perfectly elastic means there is no loss of mechanical energy. What equation does that give you?
     
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