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Conservation Laws - Finding angle ?

  1. Nov 3, 2011 #1
    Conservation Laws - Finding angle ???

    1. The problem statement, all variables and given/known data

    Having trouble with question 2, a) - See below

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    2. Relevant equations



    3. The attempt at a solution

    Which conservations laws am I suppoe to use to figure this out?

    THanks!
     
  2. jcsd
  3. Nov 3, 2011 #2

    gneill

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    Staff: Mentor

    Re: Conservation Laws - Finding angle ???

    What conservation laws do you know? Which ones are usually applied to kinematic problems?

    EDIT: @ehild: Spooky.
     
    Last edited: Nov 3, 2011
  4. Nov 3, 2011 #3
    Re: Conservation Laws - Finding angle ???

    You can use the conservation of momentum law that states the momentum before the collision is equal to the momentum after the collision. momentum being equal to mass*velocity.

    You can use the law that states that potential energy before the action is equal to the kinetic energy after the action to find the height in which the ball travelled upward.

    Those were the only two that I needed to solve the problem, good luck!
     
  5. Nov 5, 2011 #4
    Re: Conservation Laws - Finding angle ???

    Potential, can you tell me the formula you used?

    Im still having trouble with A), finding the angle?
     
  6. Nov 5, 2011 #5

    gneill

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    Staff: Mentor

    Re: Conservation Laws - Finding angle ???

    Use conservation of momentum to find the velocity immediately after the putty sticks to the wood.

    That velocity gives you the KE of the wood+putty. After that, conservation of energy (Gravitational PE vs KE) will tell you how high the wood+putty can rise. After that it's just geometry.

    Why don't you start by writing the expression for conservation of momentum that pertains to the collision?
     
  7. Nov 5, 2011 #6
    Re: Conservation Laws - Finding angle ???

    I used the formula PE=mgh and KE=(mv^2)/2
    the law states that the potential energy at the top is equal to the kinetic energy at the bottom, so mgh=(mv^2)/2

    and as for the law of momentum, Pbefore = Pafter (p is momentum) so before the collision, the only thing moving was the putty. after the collision, both the putty and the wooden ball are moving. so, Mputty*Vputty=(Mputty+Mball)*V (the velocity would be the new velocity of the ball and putty combined)
     
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