A ball with a mass of #7 kg# moving at #3 m/s# hits a still ball with a mass of #9 kg#. If the first ball stops moving, how fast is the second ball moving?

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Answer 1 · 2017-04-13T04:00:53

#2 ms^-1#

Momentum = mv

Momentum of the first ball = #7 kg times 3 m/s = 21 kg ms^-1#

Momentum is conserved.

#9 times v = 21#
#v = (21 kg ms^-1)/(9 kg#
#v = 2.3 ms^-1#

Answer 2 · 2017-04-13T06:35:54

#u_1=-0.375" "m/s#
#u_2=2.625" "m/s#

#P_1=m_1*v_1" momentum of the first object"#

#P_1=7*3=21" "kg.m/s#

#P_2=m_2*v_2" momentum of the second object"#

#P_2=9*0=0#

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

#Sigma P_b=21+0=21 " "kg*m/s#

#u_1=(2*Sigma P_b)/(m_1+m_2)-v_1" velocity of the first object after collision"#

#u_1=(2*21)/(7+9)-3#

#u_1=42/16-3#

#u_1=(42-48)/16#

#u_1=-0.375" "m/s#

#u_2=(2*Sigma P_b)/(m_1+m_2)-v_2" velocity of the second object after collision"#

#u_2=(2*21)/(9+7)-0#

#u_2=42/16#

#u_2=2.625" "m/s#