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A 5 kg ball moving to the right at 2 m/s runs into a 2 kg ball moving to the left at 5 m/s. If the collision was perfectly inelastic, what is their final speed?

User Hayat
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1 Answer

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The momentum in a coliision is conserved, since this is a perfect inelastic collision the balls will stick together after the colission then in this case we have:


m_1v_1+m_2v_2=(m_1+m_2)V

where V is the final velocity of the system. Since one ball is moving to the right and the other is moving to the right one of their velocities (the one moving to the right) is positive and the other one is negative, then we have:


\begin{gathered} 5(2)+2(-5)=(5+2)V \\ 10-10=7V \\ 7V=0 \\ V=0 \end{gathered}

Therefore their final speed is zero.

User Bob Kerns
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