A blue and a green billiard ball, each with a mass of 0.15 kg, collide directly. Before the collision, the blue ball had a speed of 3 m/s while the green ball had a speed of -2 m/s. After the collision, the blue ball stays in place while the green ball continues in motion. What is the momentum and direction of the green ball? 1.0 kg.m/s in the opposite direction from its original travel direction.

1.0 kg.m/s in the same direction from its original travel direction.
0.3 kg.m/s straight ahead
0 kg.m/s, sitting still.

1 answer

The total momentum before the collision is given by the equation:

Total momentum before = (mass of blue ball x velocity of blue ball) + (mass of green ball x velocity of green ball)
Total momentum before = (0.15 kg x 3 m/s) + (0.15 kg x -2 m/s)
Total momentum before = 0.45 kg.m/s - 0.3 kg.m/s
Total momentum before = 0.15 kg.m/s

Since momentum is conserved in a collision, the total momentum after the collision should also be 0.15 kg.m/s. Since the blue ball stays in place after the collision, the entire momentum should be carried by the green ball.

Therefore, the momentum of the green ball is 0.15 kg.m/s. Since the green ball is moving in the opposite direction from its original travel direction, the correct answer is:

1.0 kg.m/s in the opposite direction from its original travel direction.