# The Naked Scientists Forum

### Author Topic: a multiple choice question  (Read 6884 times)

#### ghh

• Jr. Member
• Posts: 48
##### a multiple choice question
« on: 17/07/2006 11:03:59 »
an object "a" with a mass "m" is moving with a velocity "v"
it collides directly with another object "b" also with mass "m", but at rest. What is the resulting velocity of object "b"?
is it
A:  0
B:  v
C:  v/2
D: all of these.

Graham

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: a multiple choice question
« Reply #1 on: 17/07/2006 13:13:47 »
Assuming an ideal elastic collision and there is no rotational enegy involved, b will move of at velocity v and a will stop. remember your snooker / pool experience

Learn, create, test and tell
evolution rules in all things
God says so!

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #2 on: 17/07/2006 20:37:30 »
Thanks Ian
I will wait for more posts before responding.
I have an agenda behind this starter.
Graham

#### Solvay_1927

• Sr. Member
• Posts: 383
##### Re: a multiple choice question
« Reply #3 on: 25/07/2006 00:52:32 »
Well go on then, ghh, you've got my attention.  What's your answer - and what's your agenda?

My answers are:

I agree with Ian - if it's a perfectly elastic collision, the answer is v.

And if it's perfectly inelastic, the answer is v/2  (although object b would arguably no longer be a separate entity - a perfectly inelastic collision would produce a new object which is an amalgamation of objects a & b, and the new object would have mass 2m and move at v/2)

These answers make the following assumptions:
- none of a's translational kinetic energy is converted into another form (e.g. heat/sound) - which is also a requirement for a perfectly inelastic/elastic collision
- there's no rotational energy, as Ian has already stated
- you're measuring everything from the point of view of an observer who remains stationary at the original point where b was at rest (i.e. not from an observer who moves with b, for example)
- the speed is low enough (relative to the speed of light) that relativistic effects can be ignored
- the objects are free from the influence of all other forces (e.g. object b isn't stuck firmly to the ground or something)

Interestingly, if object b WAS stuck immovably to the ground, then the answer would be 0 - from the point of view of an observer also standing on the ground.  But for an observer in space, the answer would be everso slightly greater than 0.  (I'll leave it for you to work out why that's the case![}:)])

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #4 on: 30/07/2006 16:22:55 »
Quote
Originally posted by Solvay_1927

Well go on then, ghh, you've got my attention.  What's your answer - and what's your agenda?

Apologies Solvay, the thread had dropped so far I hadn’t noticed someone had chipped in.
The “Agenda” was to try to induce some Lateral Thinking.
The problem I want to address is the inability for classical mechanics to describe electro-magnetic waves. Also, on the other hand the authoritative text on “quantum mechanics” manages 900 pages without a single mention of the word “gravity”.
Something is clearly rotten in the state of Physics.
The reason for this silly question is to show that the problem in classical mechanics doesn’t just apply to electro-magnetism.
Of course answer “b” gains you your “pass” in O level physics. The problem in providing the answer (d) – which you both alluded to, is that this answer depends upon my “honesty” in setting the question. If in my condition (a) if the moving mass is a bullet, and the static mass is a party balloon, then the balloon is going nowhere, except in bits!(don’t bother to elaborate, the “collision” is between the moving object and the skin of the balloon). For answer (c), if the moving object is a grapefruit, and the static object is a billiard ball, then you can get any answer <v. Answer (b) only works if the objects are of identical density, or within their structural limits for an elastic collision. In fact classical mechanics has been playing “epicycles” long before Maxwell. It has branched into Thermodynamics, gas dynamics, fluid dynamics, and materials science. In all these cases limits have to be set so that the classical mechanical relationships only work between certain parameters, (as in the medium remains a gas, or a liquid, or a solid, etc.). There is clearly a deficiency in “pure Newtonian mechanics”.

In Quantum mechanics you have the “probability wave function”, but in this case they haven’t bothered to develop the dynamics between the parameters, but merely identify the limits of the condition at the “collapse of the wave function” when the “probability” is +/- 1. In other words the same epicyclic games!
Time to move the compass point!
The reason for using the particular example is that I considered whether the definition of momentum should take account of density, in which case it would become “mass x volume, per second” or in SI units Kg.m^3.sec^-1.
When I applied this I got some startling results. I believe I can now show precisely why Atomic particle effects have to be in increments of 1/n^2, as a consequence of Gravity. – and there are surprises on the way!
I would like to post this theory when I find out how to attach a pdf to a mail!

Graham

#### Solvay_1927

• Sr. Member
• Posts: 383
##### Re: a multiple choice question
« Reply #5 on: 31/07/2006 02:57:37 »
Graham,
I'd be very interested in seeing your theory.

I must admit to being very sceptical - I thought that the law of conservation of momentum (in it's current form, mv, rather than m.d^3.s^-1) was very well demonstrated experimentally as well as theoretically - but I'm always willing to be challenged.

I don't think you can add a PDF (or other) document on these Naked Scientists postings (MODERATORS - please confirm), but you could put it on a website somewhere and give us the link. (There are lots of providers that can give you free webspace.)

Otherwise, I'd be interested in you emailing it to me (click the "send an email" link on my profile).

In the meantime, maybe you could summarise the findings of your theory in a posting here, so everyone can get a feel for it?

Ta.
Paul.

#### another_someone

• Guest
##### Re: a multiple choice question
« Reply #6 on: 31/07/2006 03:45:16 »
'fraid no way to upload any attachments.

As you say, the best thing would be to find some web space to load it up to, and then post a link to that web space.

George
« Last Edit: 31/07/2006 04:49:12 by another_someone »

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #7 on: 30/07/2006 16:22:55 »
Quote
Originally posted by Solvay_1927

Well go on then, ghh, you've got my attention.  What's your answer - and what's your agenda?

Apologies Solvay, the thread had dropped so far I hadn’t noticed someone had chipped in.
The “Agenda” was to try to induce some Lateral Thinking.
The problem I want to address is the inability for classical mechanics to describe electro-magnetic waves. Also, on the other hand the authoritative text on “quantum mechanics” manages 900 pages without a single mention of the word “gravity”.
Something is clearly rotten in the state of Physics.
The reason for this silly question is to show that the problem in classical mechanics doesn’t just apply to electro-magnetism.
Of course answer “b” gains you your “pass” in O level physics. The problem in providing the answer (d) – which you both alluded to, is that this answer depends upon my “honesty” in setting the question. If in my condition (a) if the moving mass is a bullet, and the static mass is a party balloon, then the balloon is going nowhere, except in bits!(don’t bother to elaborate, the “collision” is between the moving object and the skin of the balloon). For answer (c), if the moving object is a grapefruit, and the static object is a billiard ball, then you can get any answer <v. Answer (b) only works if the objects are of identical density, or within their structural limits for an elastic collision. In fact classical mechanics has been playing “epicycles” long before Maxwell. It has branched into Thermodynamics, gas dynamics, fluid dynamics, and materials science. In all these cases limits have to be set so that the classical mechanical relationships only work between certain parameters, (as in the medium remains a gas, or a liquid, or a solid, etc.). There is clearly a deficiency in “pure Newtonian mechanics”.

In Quantum mechanics you have the “probability wave function”, but in this case they haven’t bothered to develop the dynamics between the parameters, but merely identify the limits of the condition at the “collapse of the wave function” when the “probability” is +/- 1. In other words the same epicyclic games!
Time to move the compass point!
The reason for using the particular example is that I considered whether the definition of momentum should take account of density, in which case it would become “mass x volume, per second” or in SI units Kg.m^3.sec^-1.
When I applied this I got some startling results. I believe I can now show precisely why Atomic particle effects have to be in increments of 1/n^2, as a consequence of Gravity. – and there are surprises on the way!
I would like to post this theory when I find out how to attach a pdf to a mail!

Graham

#### Solvay_1927

• Sr. Member
• Posts: 383
##### Re: a multiple choice question
« Reply #8 on: 31/07/2006 02:57:37 »
Graham,
I'd be very interested in seeing your theory.

I must admit to being very sceptical - I thought that the law of conservation of momentum (in it's current form, mv, rather than m.d^3.s^-1) was very well demonstrated experimentally as well as theoretically - but I'm always willing to be challenged.

I don't think you can add a PDF (or other) document on these Naked Scientists postings (MODERATORS - please confirm), but you could put it on a website somewhere and give us the link. (There are lots of providers that can give you free webspace.)

Otherwise, I'd be interested in you emailing it to me (click the "send an email" link on my profile).

In the meantime, maybe you could summarise the findings of your theory in a posting here, so everyone can get a feel for it?

Ta.
Paul.

#### another_someone

• Guest
##### Re: a multiple choice question
« Reply #9 on: 31/07/2006 03:45:16 »
'fraid no way to upload any attachments.

As you say, the best thing would be to find some web space to load it up to, and then post a link to that web space.

George
« Last Edit: 31/07/2006 04:49:12 by another_someone »

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #10 on: 31/07/2006 10:20:00 »
Thanks Paul and George
I have sent you both a copy.

Occam Rules OK!
Graham

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #11 on: 01/08/2006 21:46:21 »
I have found a home for the pdf
I have stated a new thread
"one particle, two forces and four dimensions".
Enjoy!
Graham

#### ghh

• Jr. Member
• Posts: 48
##### Re: a multiple choice question
« Reply #12 on: 02/08/2006 10:41:18 »
The new thread has been moved to the new theories section
G

#### Mjhavok

• Sr. Member
• Posts: 468
##### Re: a multiple choice question
« Reply #13 on: 03/08/2006 05:51:09 »
More variables have to be decided by the question, but if I had to I would choose Velocity B:V

#### The Naked Scientists Forum

##### Re: a multiple choice question
« Reply #13 on: 03/08/2006 05:51:09 »

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