Tbr phyics momentum question

[moto_za]

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Please help me for question below. Why is answer not D?

48. A large truck, traveling due south with speed v,
collides with a small car traveling due north with the
same speed v. After the collision, the car is moving
due east, with the same speed it had prior to the collision.
What can you conclude about the final velocity of the truck?

A. It points southwest.
B. It points southeast.
C. It points south.
D. It points west.

 

[PiBond]

Please help me for question below. Why is answer not D?

48. A large truck, traveling due south with speed v,
collides with a small car traveling due north with the
same speed v. After the collision, the car is moving
due east, with the same speed it had prior to the collision.
What can you conclude about the final velocity of the truck?

A. It points southwest.
B. It points southeast.
C. It points south.
D. It points west.

Think of it in terms of conservation of momentum. Who has more momentum? The truck, because of its mass--they both have same velocity (v). At the beginning of the problem the truck's momentum outweighs the cars momentum so we have a "net" momentum going south. After they collide, the tell us that the car is heading east--therefore, I'm thinking "well I have to conserve momentum so the truck must be heading slightly west to offset our east-bound car momentum". It's only "slightly" because it's a much heavier object. Therefore, the truck should be heading south west because we have "net" momentum in the south direction initially as we previously mentioned.

Hope that helps. I'm not very eloquent when it comes to physics.

 

[echolalia16]

m1v1(truck) + m1v1 (car) = m2v2 (truck) + m2v2(car).

Because the car and truck are driving at the same velocity, we really just need to focus on their masses to determine net momentum. The "large" truck we can assume weighs more than the "small" car, so m1(truck) and m2(truck) are greater than m1(car) and m2(car). Because the car ends up going to the East (an East/West component has been added) the truck we know is going to go to the West some, but it is more massive, thus its momentum was greater than the car's. As a result, it isn't gong to go completely West, but rather Southwest, to fulfill the conservation of momentum.