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Car Speed physics question

  1. Jan 24, 2007 #1
    Can someone help me with this problem?

    Driving along a crowded freeway, you notice that it takes a time t to go from one mile marker to the next. When you increase your speed by 4.5 mi/h, the time to go one mile decreases by 11 s. What was your original speed?

    I cannot figure out how to do this problem, just the method alone would be very helpful. I kept thinking the original mile had to be in 60 sec, and I just cant figure out how to clearly go about this problem. Please help!
  2. jcsd
  3. Jan 24, 2007 #2


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    Staff: Mentor

    Use some variables to help you get going. What is the definition of speed? It's distance covered in some amount of time, right? So use V1 for the initial velocity, T1 the 11 second time, and the known D1=1 mi.

    Then V2 = V1 + 4.5 mi/h, and T2 = T1 - 11 s, and the distance is the same.

    Does that help?
  4. Jan 24, 2007 #3
    Thats basically restating what the problem says. Are there any formulas to relate them to each other, like proportions? This problem seems impossible to answer without knowing like the time it took for the first mile or some other piece of info.
  5. Jan 24, 2007 #4


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    Gold Member

    With the info that berkeman listed, I dont see how you cant the clue. You are asked to find V1:

    V1 = d/T1
    V2 = d/T2

    Cant you use the data thats listed and make things a little simpler?
    Last edited: Jan 24, 2007
  6. Jan 25, 2007 #5


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    Staff: Mentor

    ranger and I are doing our best, xsc. This an algebra problem. Show us the algrebra equations that you are having problems with, and we will try to offer help at the algebra level. You know that we do not offer solutions, correct?
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