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Basic motion stuffs, time and velociton

  1. Mar 6, 2005 #1


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    Basic motion stuffs, time and velociton :(

    oh my gosh... i can't believe i forgotten how to do this...
    i have to work out the time when will the two particles meet... where one particle (A) is travelling at a velocity of 80km/h, and (B) is travelling with a velocity of 100km/h while (B) is 350km behind (A)
    (assume they are travelling toward the same directions)

  2. jcsd
  3. Mar 6, 2005 #2
    [tex] s_a = s_b [/tex]
    [tex] s_a = s_0 + v_a * t [/tex]
    [tex] s_b = v_b * t [/tex]

    Insert both in first equation and calculate t.
  4. Mar 6, 2005 #3
    Basic algebra.

    Distance=rate x time

    so for the equation distance = rate x time just plug in x and x+350 as your distance, use t for time
    since x is the same value, you can combine the two and solve for t.
  5. Mar 6, 2005 #4


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    I'm a bit confused, do you add the 2 distances?
    [tex]x+x+350=100 \\ or \\ 80? *t?[/tex]
    Maybe I'm stupid but I'm confused...
  6. Mar 6, 2005 #5
    use relative time frames. Take the moving particles frame that is behind the other particle, subtract the other cars speed and no consider that the other particle is stationary.

    [tex] V_{slower\ particle} = 80km/h [/tex]
    [tex] V_{faster\ particle} = 100km/h [/tex]
    [tex] V_{faster\ particle\ relative\ to\ slower\ one} = 100km/h - 80km/h = 20km/h [/tex]

    now your system becomes linear.


    [tex] d = Vt [/tex]

    you should know what to sub in where.


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