A pickup truck of mass 3500 kg moving at 72 kmh-1 collides head-on with a car of mass 2000 kg moving in the opposite direction. After colliding, both the pickup and the car came to rest. (i) An 8 grade physics student commented that the law of conservation of momentum was NOT upheld in this collision, since both vehicles were moving before the collision and none of them was moving after colliding. State whether or not you agree with the student's comment and give a reason why you agree or disagree.​

Explanation:

The Law of Momentum Conservation says that the mass times the velocity of the truck + the mass times the velocity of the car BEFORE they hit has to = the mass of the tuck times the velocity of the truck + the mass of the car times the velocity of the car AFTER they hit. If we don't know the velocity of the car, we can solve for it, and then we can say that Momentum has been conserved. Before I do that, I am going to tell you that 72 kmh is 20 m/s.

The 0 is because if there is no velocity after they hit, it doesn't matter what the velocities are; anything times 0 is 0.

70,000 + 2000x = 0 where x is the velocity of the car

70,000 = -2000x so

x = -35.

As long as the car was initially traveling 35 m/s in the opposite direction )hence, the - sign), momentum is conserved. So I'm not sure exactly how you can answer this otherwise.