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Homework Help: Exponential Question?

  1. Sep 3, 2007 #1
    Exponential Question??

    1. The problem statement, all variables and given/known data

    If a car travelling at a speed of V can break at an emergency stop at a distance X. Assuming all other conditions are similar if the travelling speed of the car doubles, the stopping speed will be 4x. (I worked that out)
    A driver travelling at 40 km/h in a school zone can break to emergency stop in 3 meters. What would be the breaking distance of the car were travelling at 60 km/h.

    2. The attempt at a solution

    I have no idea how to figure this out. From what I've done, I think the number is going to be less the 7.5 but greater than 6. I'm not exactly sure how I got that though.

    Any help would be Greatly Appreciated!
  2. jcsd
  3. Sep 4, 2007 #2


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    Homework Helper

    If you solved the first one by equating the kinetic energy to a constant braking force times distance then you understand the problem. Doubling the velocity multiplies the kinetic energy by four. I don't understand why multiplying the velocity by 1.5 is throwing you for a loop. 2^2=4, 1.5^2=?
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