A ball with a mass of #7 kg# moving at #4 m/s# hits a still ball with a mass of #21 kg#. If the first ball stops moving, how fast is the second ball moving? How much kinetic energy was lost as heat in the collision?

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Answer 1 · 2017-08-21T09:58:32

The velocity of second ball is #=4/3ms^-1#. The loss of kinetic energy is #=37.33J#

We have conservation of linear momentum

#m_1u_1+m_2u_2=m_1v_1+m_2v_2#

Therefore,

#7*4+21*0=7*0+21*v_2#

#v_2=7*4/21=4/3ms^-1#

Loss of kinetic energy is

#DeltaKE=1/2m_1u_1^2-1/2m_2v_2^2#

#=1/2*7*4^2-1/2*21*4^2/3^2#

#=56-18.67=37.33J#