1. Not finding help here? Sign up for a free 30min 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!

Constrained motion problem

  1. Apr 8, 2013 #1
    1. The problem statement, all variables and given/known data

    See attached picture.


    2. Relevant equations



    3. The attempt at a solution

    I have the solution, but I'm puzzled by the first step in their solution, which reads

    Xa^(2) + Xb^(2) = L^(2)

    The solution provider then takes the time derivative of this expression which then produces

    2Xa(Xa(dot))+2Xb(Xb(dot)) = 0

    where Xa(dot) and Xb(dot) is the Xa or Xb symbol with a dot over it.

    Thanks for you're assistance!
     

    Attached Files:

    Last edited by a moderator: Apr 10, 2013
  2. jcsd
  3. Apr 8, 2013 #2
    Here is the solution if my explanation was confusing in any way.
     

    Attached Files:

  4. Apr 8, 2013 #3
    Any help would be greatly appreciated.
     
  5. Apr 9, 2013 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    I don't understand what's puzzling you. The first line is just Pythagoras' theorem applied to the triangle of which AB is the hypotenuse.
     
  6. Apr 9, 2013 #5
    The line below it, when taking the time derivative of the first line how do they end up with that expression?
     
  7. Apr 9, 2013 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    If x = x(t), can you write down the expression for (d/dt)x2?
     
  8. Apr 10, 2013 #7
    2x? or x(t)dx/dt = x(t)*x'(t)
     
  9. Apr 24, 2013 #8
    How did you know that x was a function of time?
     
  10. Apr 24, 2013 #9

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    No, but each answer you offer is half right. Do you know the chain rule?
     
  11. Apr 25, 2013 #10
    yep, i understand now haruspex, thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Constrained motion problem
  1. Problem on motions (Replies: 1)

  2. Motion problem (Replies: 5)

Loading...