Momentum Problem, please help!?

Question

On a horizontal frictionless table, masses A and B (3 kg, 6 kg) slide to the right and left, respectively. They have speeds of 3 m/s and 1 m/s, respectively. The two masses collide, and bounce off each other. After the collision, they travel in opposite directions at speeds of 1.5 m/s and 1.250 m/s, respectively.
(Note:In this problem, please use + dir = right, - dir = left, to indicate direction.)

a.) Calculate A's momentum:
before collision:
after collision:
Explain why it is NOT conserved.


b.) Calculate B's momentum:
before collision: kg*m/s
after collision: kg*m/s
Explain why it is NOT conserved.


c.) Calculate the A+B system's momentum:
before collision: kg*m/s
after collision: kg*m/s
Explain why IS it conserved.


d.) Calculate the kinetic energy of the A+B system:
before collision: J
after collision: J

Answer 1

a)
Before
3*3=9 kgm/s
after
3*(-1.5)= -4.5 kgm/s

not conserved because of the collision and movement of B

b)
Before
6*(-1)=-6
After
6*1.25=7.5
not conserved because of the collision and movement of A

c)
Before
9-6=3
after
7.5-4.5=3

conserved because the center of mass of any collision follows the Law of Momentum Conservation

d) Before
.5*3*9+.5*6*1
16.5 J

After
.5*3*1.5^2+.5*6*1.25^2
8.0625 J
Not conserved = inelastic collision

j