A ball with a mass of #3 kg# moving at #7 m/s# hits a still ball with a mass of #10 kg#. If the first ball stops moving, how fast is the second ball moving?

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Answer 1 · 2016-04-29T09:48:37

#v_2^'=2,1 m/s#

#"if collision elastic and centered :"#
#vec P_1=m_1*v_1" momentum before collision for the first object"#
#vec P_1=3*7=21 " "kg*m/s#

#vec P_2=m_2*v_2" momentum before collision for the second object"#
#vec P_2=10*0=0#

#vec P_b=vec P_1+vec P_2" total momentum before collision"#

#P_b=21+0=21#

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

#vec P_1^'=3*0=0#

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

#vec P_2^'=10*v_2^'#

#P_a=P_1^'+P_2^'" total momentum after collision"#

#P_a=0+10*v_2^'#

#P_b=P_a" conservation of momentum"#

#21=10*v_2^'#

#v_2^'=21/10#

#v_2^'=2,1 m/s#