A ball with a mass of #4 kg # and velocity of #1 m/s# collides with a second ball with a mass of #5 kg# and velocity of #- 8 m/s#. If #25%# of the kinetic energy is lost, what are the final velocities of the balls?

1 Answer
Mar 28, 2017

Approximately 5.20 meters per second

Explanation:

Kinetic energy formula is #E= 0.5*m*v*v#
m is for mass (kg) and v is for velocity (m/s).
The first ball's kinetic energy is #E1=2 kg*m*m/(s*s)#
The second ball's kinetic energy is #E2=160 kg*m*m/(s*s)#
Total energy when they collide is #E=162 kg*m*m/(s*s)#

However only 75% of this value is saved after collision of these balls. In other words total kinetic energy after collision is #121.5 kg*m*m/(s*s)#

Final mass of these balls #9 kg# but what is final velocity?

#121.5 kg*m*m/(s*s) = 0.5*9*v*v#

#27 = v*v#

#5.196 = v# (as m/s).

This is the answer of the velocity of the final ball (9 kg). It moves similar to the direction of the second ball with a lower speed.