Two cars collide at an intersection. one car has a mass of 900 kg and is moving 10 m/s to the north, while the other has a mass of 1000 kg and is moving 7 m/s to the south. what is their combined momentum?

2000 kgm/s to the north.  

Explanation:

For any   colliding bodies, momentum must be conserved.

In this case we are required to find the momentum before collision.

Since the two cars are moving to different direction, we are going to take one velocity as negative.

∴ (900×10) + (1000× -7) = 9000 + - 7000

                                       = 9000 - 7000

                                       = 2000 kgm/s

Since the answer is positive and we had taken the velocity due north as positive, the combined momentum is 2000 kgm/s to the north.  

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