19. A ball with a mass of 2 kg moves to the right at a speed of 0.28 m/s. It hits a ball of mass 0.5 kg which is at rest. After collision, the second ball moves to the right with a speed of 1.5 m/s. What is the speed and direction of the first ball after collision?

Answer 1

momentum before = 2 *.28

momentm after = 2 v + .5 * 1.5

.56 = 2 v + .75
2 v = -.19
v = - .095 (The Answer :)

Now by the way is this possible?
initial kinetic energy = (1/2)2 (.28)^2 = .0784 Joules

final Ke = (1/2)(2)(-.095)^2 + (1/2)(.5)(2.25)

= .009025 + .5625 = .5715 Joules

So despite momentum being conserved and an answer obtained, the solution is impossible because the system somehow gained energy during the collision :)