Inelastic Collision Between Two Bodies

[aceking3150]

Homework Statement

It's given through a passage that a leukocyte has a mass of 8x10^-10 and platelet has a mass of 1x10^-11 indicating that they DO have very different masses. But am i wrong by saying that they have a common final momentum since they stick together after colliding? Wouldn't they have both a common final velocity AND a common final momentum since they would have a combined mass of 8.1×10−10. I've missed a few problems like this and I don't get whether I am misunderstanding something or they have them incorrect.

Relevant Equations

m1v1+m2v2 = (m1+m2)v'

 

[PeroK]

If the masses are different the momenta must be different for a common velocity. Unless that velocity is zero.

 

[Bandersnatch]

The question basically asks whether $m_1v'$ equals $m_2v'$.

 

[aceking3150]

I see how the masses are different, but if a perfectly inelastic collision is when the two stick together, wouldn't their masses combine into one? I see how if you look at them with separate masses even after they collide they would have different momenta. But, even though they've stuck together, their masses can be considered separate? I feel like that's what's confusing me.

 

[PeroK]

I see how the masses are different, but if a perfectly inelastic collision is when the two stick together, wouldn't their masses combine into one? I see how if you look at them with separate masses even after they collide they would have different momenta. But, even though they've stuck together, their masses can be considered separate? I feel like that's what's confusing me.

Does that mean that you are not you when you are in a car? Have you and the car merged into a single mass?

If the two cells are considered a common entity after the collision, then it would make no sense to ask about them as separate cells any more. The question would be something like: "what is the momentum of the final object?"

You may not be crazy, but I think you are having an existential crisis.

 

[HallsofIvy]

You appear to be misunderstanding the question. Yes, the two stick together so have the same velocity and can be considered to be a single object with mass m1+ m2 and momentum (m1+ m1)v. But "III" specifically says "the two cells will have a common final momentum" (emphasis mine). It is clearly talking about the two separate cells which have different momenta.

(I can't speak to whether you are crazy or not. But you are wrong. The correct answer is B.)

 

[aceking3150]

Does that mean that you are not you when you are in a car? Have you and the car merged into a single mass?

If the two cells are considered a common entity after the collision, then it would make no sense to ask about them as separate cells any more. The question would be something like: "what is the momentum of the final object?"

You may not be crazy, but I think you are having an existential crisis.

Ahhhhh, OK. I see what you mean now. I'm probably thinking of them as combining because my book has given so many examples of them combining entirely.

And as far as an existential crisis, you might be right, haha. Seeing as physics is my weakest area and I'm taking the MCAT in two weeks. :|