Vector diagram - particle collision

*jsmith613*

1. The problem statement, all variables and given/known data

see attached image

2. Relevant equations

3. The attempt at a solution

So I know as it is a VECTOR diagram it must either be B or C

So I checked that 1, 2, 3, 4 all pointed in the correct directions and they do in both diagrams.
I chose B (but at random) and the answer was C.
Why is the answer C?

thanks

Infinitum

Hi jsmith!!

Use the conservation of momentum, this tells you the initial total momentum should be equal to the final total momentum. In which of the options, do you see this??

*dimension10*

Quote by jsmith613

1. The problem statement, all variables and given/known data

see attached image

2. Relevant equations

3. The attempt at a solution

So I know as it is a VECTOR diagram it must either be B or C

So I checked that 1, 2, 3, 4 all pointed in the correct directions and they do in both diagrams.
I chose B (but at random) and the answer was C.
Why is the answer C?

thanks

First of all, is this supposed to be a Classical Mechanics question or a Quantum mechanics question? Because if it is Classical mechanics, then the question is impossible. But in Quantum mechanics, it is possible.

*jsmith613*

Quote by dimension10

First of all, is this supposed to be a Classical Mechanics question or a Quantum mechanics question? Because if it is Classical mechanics, then the question is impossible. But in Quantum mechanics, it is possible.

??? classical mechanism

why is it impossibel?

*dimension10*

Quote by jsmith613

??? classical mechanism

why is it impossibel?

I'm assuming the mass is constant?

*jsmith613*

Quote by Infinitum

Hi jsmith!!

Use the conservation of momentum, this tells you the initial total momentum should be equal to the final total momentum. In which of the options, do you see this??

momentum is consereved in B??

*dimension10*

Quote by jsmith613

momentum is consereved in B??

How is momentum conserved in B

*jsmith613*

Quote by dimension10

How is momentum conserved in B

resultant momentum of both is in the same direciton, no?

*dimension10*

Quote by jsmith613

resultant momentum of both is in the same direciton, no?

In classical mechanics, you have ##m_1v_{1i}+m_2v_{2i}=m_1v_{1f}+m_2v_{2f}## but that does not hold in the question, so I think it is a Quantum mechanics question...

Infinitum

Quote by jsmith613

resultant momentum of both is in the same direciton, no?

Uh nope, it isn't. And you can't be sure about the direction in B as the exact magnitude and direction of original aren't given.

Also, direction isn't the only necessary factor. The magnitude remains same too. Observe C carefully.

*jsmith613*

Quote by dimension10

In classical mechanics, you have ##m_1v_{1i}+m_2v_{2i}=m_1v_{1f}+m_2v_{2f}## but that does not hold in the question, so I think it is a Quantum mechanics question...

I just reaslied that i have to apply head-to-tail rule
if I apply this it ALWAYS works for ALL questions that have bothered me in the past
:)

Infinitum

Quote by dimension10

In classical mechanics, you have ##m_1v_{1i}+m_2v_{2i}=m_1v_{1f}+m_2v_{2f}## but that does not hold in the question, so I think it is a Quantum mechanics question...

I believe classical mechanics does hold in the question....

Infinitum

Quote by jsmith613

I just reaslied that i have to apply head-to-tail rule

Yes!! That's it!

*dimension10*

Quote by Infinitum

I believe classical mechanics does hold in the question....

Then I don't think I understood the question properly. What I understand of it is:

$$v_{1i}=1$$
$$v_{2i}=2$$
$$v_{1f}=3$$
$$v_{2f}=4$$
$$m_1,m_2=\mbox{Constant}$$

Infinitum

Quote by dimension10

Then I don't think I understood the question properly. What I understand of it is:

$$v_{1i}=1$$
$$v_{2i}=2$$
$$v_{1f}=3$$
$$v_{2f}=4$$
$$m_1,m_2=\mbox{Constant}$$

You didn't read the question properly

1, 2, 3, 4 are the momenta before and after collision, not the velocities.

*dimension10*

Quote by Infinitum

You didn't read the question properly

1, 2, 3, 4 are the momenta before and after collision, not the velocities.

Oh! I didn't see that!

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Infinitum	Hi jsmith!! Use the conservation of momentum, this tells you the initial total momentum should be equal to the final total momentum. In which of the options, do you see this??