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Elastic and Inelastic Collisions

AP Physics 1· difficulty 4/5

A 1.0 kg ball at 4.0 m/s strikes a stationary 3.0 kg ball in a perfectly elastic head-on collision. The 3.0 kg ball moves off at

  • A

    4.0 m/s

  • B

    2.0 m/s (v2′=2m1v1/(m1+m2)v_2' = 2 m_1 v_1 / (m_1 + m_2))

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  • C

    3.0 m/s

  • D

    1.0 m/s

Explanation

Standard 1D elastic formula: v2′=2m1v1/(m1+m2)=2(1)(4)/(1+3)=2.0v_2' = 2 m_1 v_1/(m_1 + m_2) = 2(1)(4)/(1+3) = 2.0 m/s. (And v1′=(m1−m2)v1/(m1+m2)=−2v_1' = (m_1 - m_2)v_1/(m_1 + m_2) = -2 m/s — bounces back.)

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