A 5.00 kg ball is moving at 4.0 m/s to the right and a 6.00 kg ball is moving at 3.00 m/s to the left. The total momentum of the system is
A) 2.0 kg m/s to the right.
B) 2.0 kg m/s to the left.
C) 38 kg m/s to the right.
D) 18 kg m/s to the left.
E) 20 kg m/s to the right.

Question

Quizplus · Accepted Answer

The total momentum of the system can be calculated by adding the momentum of each ball, taking direction into account. The momentum of the 5.00 kg ball is $5.00 \, \text{kg} \times 4.0 \, \text{m/s} = 20 \, \text{kg m/s}$ to the right, and the momentum of the 6.00 kg ball is $6.00 \, \text{kg} \times 3.00 \, \text{m/s} = 18 \, \text{kg m/s}$ to the left. Subtracting these (since they are in opposite directions), the total momentum is $20 \, \text{kg m/s} - 18 \, \text{kg m/s} = 2.0 \, \text{kg m/s}$ to the right.

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