IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: Dania on September 25, 2010, 08:41:58 pm

Title: Momentum Question
Post by: Dania on September 25, 2010, 08:41:58 pm
Hi, can someone please explain to me fully, with and example [or any other method] what is meant by:

"Relative speed of approach = Relative speed of separation".

[I know it's silly, but I'm having problems trying to apply this principle]

Thanks :)
Title: Re: Momentum Question
Post by: astarmathsandphysics on September 25, 2010, 11:54:38 pm
Not really to do with momentum more restitution. I have done a page on my website. Will post a link first thing in morning.
Title: Re: Momentum Question
Post by: Deadly_king on September 26, 2010, 08:12:50 am
Quote from: Danii on September 25, 2010, 08:41:58 pm
Hi, can someone please explain to me fully, with an example [or any other method] what is meant by:

"Relative speed of approach = Relative speed of separation".

[I know it's silly, but I'm having problems trying to apply this principle]

Thanks :)

In other words it also implies that total kinetic energy is conserved.

Relative speed of approach is the difference between the speed of two particles which will be colliding in a matter of time.

Relative speed of separation is the difference between the speed of the two particles after collision.

Example : Nov 08 P1 No 10
Since collision is elastic the two particles will not merge after collision. Each will move separately at a certain speed such that total k.E is conserved.
For the two spheres not to merge ----> V2 > V1
Relative speed of approach = Relative speed of separation
u1 - (-u2) = v2 - v1

For this question....Answer is therefore D.

NOTE : u2 is taken to be negative since it moves in opposite direction.

If you have time......take a close look at this link.....it might help clear your doubts :)
http://thatlaureltree.blogspot.com/2008_03_01_archive.html
Title: Re: Momentum Question
Post by: Dania on September 26, 2010, 08:32:08 am
Thank you, that was really helpful :)
Title: Re: Momentum Question
Post by: Deadly_king on September 26, 2010, 08:35:37 am
Quote from: Danii on September 26, 2010, 08:32:08 am
Thank you, that was really helpful :)
You are most welcome :)

And don't worry it was not a silly question since many students get misguided by the question :P

I was one of them too  ;)
Title: Re: Momentum Question
Post by: astarmathsandphysics on September 26, 2010, 09:18:17 am
http://www.astarmathsandphysics.com/a_level_maths_notes/M2/a_level_maths_notes_m2_restitution_momentum_collisions.html