Results 1 to 4 of 4

Thread: Relative velocity question

  1. #1
    Newbie
    Joined
    Mar 2018
    From
    London
    Posts
    2

    Relative velocity question

    Lets say if I have particle P with velocity Vp which is intercepting another particle Q with velocity Vq. For the particles to intercept, should the velocity of P relative to Q (Vp-Vq) always be pointing towards Q? My textbook says:

    We 'fix the target' by applying the vector -Vq to Q, but we must also apply this vector to P as well, ending up with Vp-Vq= pVq, which points towards the position of Q when it is stationary.

    Can some please explain
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Nov 2010
    Posts
    3,715
    Thanks
    1510

    Re: Relative velocity question

    I am not understanding your notation. Do you have a specific example they give? Specifically, what does $pVq$ mean? You have a point $P$, and a velocity $V_p$, but you do not have a value $p$. Is that a scalar or vector? How many dimensions are you working with? This question is obviously much easier to answer in two dimensions than it is in three. What do you mean by "intercept"? What type of particle collisions are you working with? Are there glancing collisions? Or after an "interception", do you have two particles acting as one (sort of a fusion of the two)?
    Last edited by SlipEternal; Mar 5th 2018 at 01:09 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2018
    From
    London
    Posts
    2

    Re: Relative velocity question

    Relative velocity question-pic1.jpgRelative velocity question-pic2.jpg

    pVq means the velocity of P relative to Q.
    We are working in two dimensions
    By intercept, we are just talking about whether they would meet in their trajectories. I really do not understand the stuff they said in the second picture Why did they just reduce the velocity of Q to 0 and add its vector onto P? Please could you, if possible, explain it in layman terms as I've been trying to make sense of this for ages!
    Last edited by bindra; Mar 5th 2018 at 03:41 PM.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Nov 2010
    Posts
    3,715
    Thanks
    1510

    Re: Relative velocity question

    Quote Originally Posted by bindra View Post
    Click image for larger version. 

Name:	pic1.jpg 
Views:	6 
Size:	162.8 KB 
ID:	38557Click image for larger version. 

Name:	pic2.jpg 
Views:	6 
Size:	150.5 KB 
ID:	38558

    pVq means the velocity of P relative to Q.
    We are working in two dimensions
    By intercept, we are just talking about whether they would meet in their trajectories. I really do not understand the stuff they said in the second picture Why did they just reduce the velocity of Q to 0 and add its vector onto P? Please could you, if possible, explain it in layman terms as I've been trying to make sense of this for ages!
    Imagine empty space where there are no points of reference. You have two particles moving around. To the observer outside the system, we can observe the two particles moving around. Suppose you were sitting on one of the objects. To you, you have no frame of reference to determine if you are moving or not. Your only frame of reference is the other particle. You watch the other particle move with respect to you, but as far as you are concerned, you are at rest while sitting on your particle. Since you cannot view the whole system, but only your reference from your perch atop your one particle, you cannot see that you, too, are moving.

    Now, add in the rest of the world. You now have more frames of reference. But, you remember that feeling of being "stationary". Now, you watch the world zipping by you. Is it you that is moving? Or is it the world moving beneath you? So long as you use a consistent frame of reference, physics does not care which reference you use. The math will work out every which way. This example was showing you that.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. relative velocity
    Posted in the Advanced Applied Math Forum
    Replies: 9
    Last Post: Jul 17th 2017, 06:04 AM
  2. relative velocity
    Posted in the Advanced Applied Math Forum
    Replies: 4
    Last Post: Mar 18th 2017, 03:57 AM
  3. Relative Velocity Question
    Posted in the Advanced Applied Math Forum
    Replies: 4
    Last Post: Apr 2nd 2010, 12:26 AM
  4. Extremely difficult question on relative velocity?
    Posted in the Advanced Applied Math Forum
    Replies: 1
    Last Post: Sep 2nd 2008, 09:45 AM
  5. relative velocity (physics question)
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: Mar 5th 2008, 07:16 AM

Search Tags


/mathhelpforum @mathhelpforum