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Math Help - How to calculate the final velocity.

  1. #1
    TGS
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    How to calculate the final velocity.

    A bullet of mass 0.205 kg traveling horizontally at a speed of 250 m/s embeds itself in a block of mass 3.5 kg that is sitting at rest on a nearly frictionless surface.

    What is the speed of the block after the bullet embeds itself in the block?
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  2. #2
    Flow Master
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    Quote Originally Posted by TGS View Post
    A bullet of mass 0.205 kg traveling horizontally at a speed of 250 m/s embeds itself in a block of mass 3.5 kg that is sitting at rest on a nearly frictionless surface.

    What is the speed of the block after the bullet embeds itself in the block?
    Use conservation of momentum.
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  3. #3
    TGS
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    I've already tried that... I got it wrong.
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    Quote Originally Posted by TGS View Post
    I've already tried that... I got it wrong.
    Please show your work and I will review it.
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  5. #5
    TGS
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    m_1 v_{1i} + m_2 v_{2i} = m_1 v_{1f} + m_2 v_{2f}

    m_1 v_{1i} + 0 = 0 + m_2 v_{2f}

    (0.205 kg) (250m/s) = (3.5kg) (v_{2f})

    v_{2f} = 14.643
    Last edited by mr fantastic; September 25th 2009 at 06:44 PM. Reason: Improved the latex and formatting
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  6. #6
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    Quote Originally Posted by TGS View Post
    m_1 v_{1i} + m_2 v_{2i} = m_1 v_{1f} + m_2 v_{2f}

    m_1 v_{1i} + 0 = 0 + m_2 v_{2f}

    (0.205 kg) (250m/s) = (3.5kg) (v_{2f}) Mr F says: Your mistake is here.

    v_{2f} = 14.643
    Since the bullet is embedded in the block, the correct equation is (0.205 kg) (250) = (3.5 + 0.205) (v_{2f}) ....
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  7. #7
    TGS
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    ohhhhh... thank you.
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