A ball with a mass of # 6 kg# is rolling at #7 m/s# and elastically collides with a resting ball with a mass of #3 kg#. What are the post-collision velocities of the balls?

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Answer 1 · 2016-05-11T20:31:28

#v_1^'=7/3 m/s#
#v_2^'=28/3 m/s#

#6*7+3*0=6*v_1^'+3*v_2^'" conservation of momentum"#

#42=6*v_1^'+3*v_2^'" "(1)#

#v_1+v_1^'=v_2+v_2^'" conservation of the kinetic energy"#

#7+v_1^'=0+v_2^'" (2)"#

#42=6*v_1^'+3(7+v_1^')#

#42=6v_1^'+21+3v_1^'#

#42-21=9v_1^'#

#21=9v_1^'#

#v_1^'=21/9#

#v_1^'=7/3 m/s#

#"use (2)"#

#7+7/3=v_2^'#

#v_2^'=28/3 m/s#