A ball with a mass of #2 kg# moving at #18 m/s# hits a still ball with a mass of #7 kg#. If the first ball stops moving, how fast is the second ball moving?

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Answer 1 · 2016-07-06T21:14:29

#vec v_2^'=5.12" "m/s" (rounded to two decimal place)"#

#vec P_1=m_1*vec v_1" the first object's momentum before collision"#

#vec P_1=2*18=36" "kg.m/s#

#vec P_2=m_2*v_2" the second object's momentum before collision"#

#vec P_2=7*0=0#

#Sigma vec P_b=vec P_1+vec P_2" the vectorial sum of momentums before collision"#

#Sigma vec P_b=36+0=36 " "kg*m/s#

#vec P_1^'=m_1*v_1^'" the first object's momentum after collision"#

#vec P_1^'=2*0=0#

#vec P_2^'=m_2*v_2^'" the second object's momentum after collision"#

#vec P_2^'=7*v_2^'#

#Sigma vec P_a=P_1^'+P_2^'" the vectorial sum of momentums after collision"#

#vec P_a=0+7*v_2^'=7v_2^'#

#Sigma P_b=Sigma P_a#
#"Momentum is reserved because collision is elastic."#

#36=7*vec v_2^'#

#vec v_2^'=36/7#

#vec v_2^'=5.12" "m/s" (rounded to two decimal place)"#