1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Particle Motion

  1. Mar 31, 2012 #1
    1. The problem statement, all variables and given/known data
    A particle moves in a straight line away from a fixed point O in the line, such that when its distance from O is x its speed v is given by v=k/x , for some constant k.

    (a) show that the particle has a retardation which is inversely proportional to x3
    The answer is -k2*x-3

    (b) if a,b,c,d are points in that order on the straight line, such that the distances ab, bc, cd are all equal, show that the times taken to travel these successive distances increase in arithmetic progression.

    2. Relevant equations
    Possible the answer to the first one comes into relevance, -k2*x-3

    3. The attempt at a solution
    let the four points have x coordinates
    x, x+xo , x+2xo , x+3xo
    Last edited: Mar 31, 2012
  2. jcsd
  3. Mar 31, 2012 #2


    User Avatar
    Homework Helper

    For part a) how would you find the retardation ? (negative acceleration)

    (Hint: use the chain rule to express 'a' in terms of 'v' and 'x')

    For part b) try finding time based on t= distance/velocity at the given points.
  4. Apr 1, 2012 #3
    I still can't figure it out :L
  5. Apr 1, 2012 #4


    User Avatar
    Homework Helper

    If a=dv/dt, can you use the chain rule to re-write this in terms of v and x? (Hint: you will have to have a dv/dx term)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook