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Homework Help: Calculating when 2 points meet

  1. Jun 21, 2010 #1
    1. The problem statement, all variables and given/known data
    Runner A runs at 6.0m/s for 10s. Runner B accelerates from 4.0 m/s to 10.0 m/s steadily in 10s. How far does Runner A go in 10s? How far does Runner B go in 10s? At what time did Runner B pass Runner A if they were both at the same position at t=0?

    2. Relevant equations
    d= v*t, d = 1/2(v1+v2)*t

    3. The attempt at a solution

    Runner A:
    d = v*t
    d = (6.0m/s)(10s)
    d = 60m

    Runner B:
    d = 1/2(v1+v2)*t
    d = 1/2(4m/s+10m/s)*(10s)
    d = 1/2(14m/s)*(10s)
    d= 70m

    so therefore at 10s, Runner B has already surpassed Runner A by 10m. But how would you find when Runner B passed Runner A?

    Many thanks.
  2. jcsd
  3. Jun 21, 2010 #2
    Do you see that you want to find t such that vt = ½(v1+v2)t? How can you write v2 in terms of t?
  4. Jun 21, 2010 #3
    im sorry. i dont understand..
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