Question

MEDAL GIVEN TO CORRECT ANSWER.
Two cars collide with each other. Before the collision, one car (m = 1000 kg) is going north at 20 m/s and the other car (m = 1200 kg) is going south at 25 m/s. What is the momentum of the system made up of the two cars after the collision?

A. 10,000 kgm/s north
B. 50,000 kgm/s south
C. 50,000 kgm/s north
D. 10,000 kgm/s south

Answer 1

Momentum before the collision must equal the momentum after the collision. Conservation of momentum is universally true. Basically, work out the momentum before the collision, this is has to be the momentum afterwards.

Answer 2

Basically, the momentum before the collision will equal the momentum after the collision (Conservation of momentum).

So let's find the initial momentum:
Both cars are traveling in OPPOSITE directions, so we must subtract. Furthermore, please note that I am using "north" as the positive direction and "south" as the negative direction.

(20,000 kgm/s) - (30,000 kgm/s) = -10,000 <------- Negative answer

Because I chose "south" to be the negative direction, this means that the correct direction must be "south".

The correct answer then must be D.

Answer 3

Answer D. 10,000 kgm/s south

Answer 4

Please let me know if you have any questions!