A ball with a mass of #2 kg# moving at #8 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? How much kinetic energy was lost as heat in the collision?

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Answer 1 · 2017-03-22T17:53:40

The velocity of the second ball #=1.78ms^-1#
The kinetic energy lost is #=49.8J#

Momentum is conserved

#m_1u_1+m_2u_2=m_1*v_1+m_2v_2#

#u_2=v_1=0#

#m_1u_1=m_2v_2#

#v_2=m_1/m_2*u_1#

#=2/9*8=16/9=1.78ms^-1#

#KE# before is #=1/2m_1u_1^2=1/2*2*8^2=64J#

#KE# after is #=1/2m_2v_2=1/2*9*1.78^2=14.2J#

Loss in #KE# is #=64-14.2=49.8J#