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?

A. 2000 kgm/s south
B. 2000 kgm/s north
C. 16,000 kgm/s north
D. 16,000 kgm/s south

Question

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?

 		A.	2000 kgm/s south
 		B.	2000 kgm/s north
 		C.	16,000 kgm/s north
 		D.	16,000 kgm/s south

anonymous · Answer

(900 kg)(10 m/s) - (1000 kg)(7 m/s) = combined. 

If > 0, then north
If < 0 then south.

anonymous · Answer

i got 2,000 kgm/s north. 
is that correct? @douglaswinslowcooper

anonymous · Answer

Just so!

anonymous · Answer

this question is kind of alike, do i solve it the same? 
Two birds collide in midair. Before the collision, their combined momentum was 15 kgm/s to the north. What is their combined momentum after the collision? @douglaswinslowcooper

anonymous · Answer

Principle is the same: unless there is an external force to change the total momentum of the system, it remains the same total before and after the collision.

anonymous · Answer

so it would still be 15 kgm/s , and it would be north as well? @douglaswinslowcooper

anonymous · Answer

Yes, indeed.