Vector diagram - particle collision

[jsmith613]

Homework Statement

see attached image

Homework Equations

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]

Homework Statement

see attached image

Homework Equations

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]

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]

? classical mechanism

why is it impossibel?

I'm assuming the mass is constant?

 

[jsmith613]

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]

momentum is consereved in B??

How is momentum conserved in B

 

[jsmith613]

How is momentum conserved in B

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

 

[dimension10]

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]

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]

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]

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]

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

Yes! That's it!

 

[dimension10]

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]

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]

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!