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Math Help - Momentum and collisions question.

  1. #1
    Junior Member silvercats's Avatar
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    Momentum and collisions question.

    2 objects called A and B are weighted.3KG and 2KG.A has 2m/s velocity and B has 6m/s before the collision and they collide face to face.after the collision ,object A moves to opposite direction with a speed of 4m/s.What is the velocity of B after the collision?

    answer has to be 15m/s.But I never get it


    here how i did it
    put m1u1+m2u2=m1v2+m1v2 to the right

    3kg * 2m/s + 2kg *( -6m/s) = 3kg * (-4m/s)+2v
    =6-12=-12+2v
    v=3m/s not 15
    Last edited by mr fantastic; April 23rd 2011 at 01:31 PM. Reason: Title.
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  2. #2
    Senior Member abhishekkgp's Avatar
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    Quote Originally Posted by silvercats View Post
    2 objects called A and B are weighted.3KG and 2KG.A has 2m/s velocity and B has 6m/s before the collision and they collide face to face.after the collision ,object A moves to opposite direction with a speed of 4m/s.What is the velocity of B after the collision?

    answer has to be 15m/s.But I never get it


    here how i did it
    put m1u1+m2u2=m1v2+m1v2 to the right

    3kg * 2m/s + 2kg *( -6m/s) = 3kg * (-4m/s)+2v
    =6-12=-12+2v
    v=3m/s not 15
    looks right... you sure that 4m/s is not relative velocity of A w.r.t B after the collision.
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  3. #3
    Junior Member silvercats's Avatar
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    Quote Originally Posted by abhishekkgp View Post
    looks right... you sure that 4m/s is not relative velocity of A w.r.t B after the collision.
    yup.
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  4. #4
    Senior Member abhishekkgp's Avatar
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    Quote Originally Posted by silvercats View Post
    yup.
    well then i can't find any mistakes if the collision is one dimensional.
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  5. #5
    Junior Member silvercats's Avatar
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    I think books's answer must be wrong.I got the same thing too .thanx!
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