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Homework Help: One dimensional motion problems

  1. Aug 27, 2009 #1
    1. The problem statement, all variables and given/known data
    1) Runner A is initially 4.0 mi west of a flagpole and is running with a constant velocity of 6.0 mi/h due east. Runner B is initially 3.0 mi east of the flagpole and is running with a constant velocity of 5.0 mi/h due west. How far are the runners from the flagpole when they meet?

    2) A train is traveling down a straight track at 20 m/s when the engineer applies the brakes, resulting in an acceleration of -1.0 m/s^2 as long as the train is in motion. How far does the train move during a 40 s time interval starting at the instant the brakes are applied?

    2. Relevant equations
    1) V=Vi + at
    2) x=Vit + 1/2at^2
    3) V^2=Vi^2 + 2ax
    4) a=V/t
    5) v=x/t

    3. The attempt at a solution
  2. jcsd
  3. Aug 28, 2009 #2
    1) Can you find the displacement (with respect to the flagpole) of each runner at any given time? When they meet, what must their displacement be?

    2) How long does it take for the train to stop with the given acceleration? Thus how far would it have travelled?
  4. Sep 17, 2009 #3
    Set up an equation with respect to the flagpole being zero. If runner a is 4mi west (-4miles) and running 6mi/h east (+6mi/h) and runner b is 3 miles east (+3miles) running at 5mi/h west (-5mi/hr), then you can set them equal to each other to find when they meet. -4+6x=3-5x then x=.64 Then plug .64 back into one side of the equation (3-5(.64))= -.2 miles (.2 miles west). Thats how I got the right answer for my webassign.
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