A ball with a mass of #4 kg # and velocity of #3 m/s# collides with a second ball with a mass of #2 kg# and velocity of #- 1 m/s#. If #20%# of the kinetic energy is lost, what are the final velocities of the balls?

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Answer 1 · 2017-03-31T09:31:40

2.13 m/s

The energy of the first ball #E=0.5*m*v^2 = 18 kg.m^2/s^2#

The energy of the second ball #E=-1 kg*m^2/s^2#

Total energy when they collide #E=17 kg*m^2/s^2#

Now the net energy (after 20% becomes heat energy) #= 17*0.8=13.6 kg*m^2/s^2#

Total mass is 6 kg. Compute the velocity:

#13.6 = 0.5*6*v^2#

#v = 2.13 m/s#. On the first ball direction.