Two objects of equal mass are moving with equal speeds in the horizontal plane. They collide and move off together (perfectly inelastic collision) at...

 Two objects of equal mass are moving with equal speeds in the horizontal plane. They collide and move off together (perfectly inelastic collision) at half the value of their original speed. (a) What is the angle between their initial velocities? {120o} (b) What percentage of the kinetic energy remains after the collision?