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Formula for time to distance from stop

  1. Nov 1, 2007 #1

    jph

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    Can someone please post the formula I need to use to determine the time it takes for a vehicle to start from a stopped position on a paved asphalt roadway (coef of approx .70), a grade of +3 degrees, and accelerate to a known distance?

    Thanks for any help.

    jph
     
  2. jcsd
  3. Nov 2, 2007 #2

    Shooting Star

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    Is this a homework question? In that case, you write what you have done so far.
     
  4. Nov 2, 2007 #3

    HallsofIvy

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    As stated this doesn't make a whole lot of sense. Since you give the "coefficient" (of friction?) I suppose we are to calculate the acceleration from force but you haven't told us the force exerted by the engine.
     
  5. Nov 2, 2007 #4

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    I think the vehicle is simply rolling downhill. Let the OP present the problem clearly.
     
  6. Nov 2, 2007 #5

    jph

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    Drive down

    This is not for homework or a class assignment. I'm trying to resolve a hunch on how a motor vehicle accident happened. I believe it was intentionally created, called a "drive down."

    I am aware of some speed formulas and can derive them from KE=FR.

    I believe that there is a formula that will allow me to determine the time it takes for a vehicle to accelerate from a stop to a given distance, and that it is dependent upon the force, rate of acceleration, etc. and I likely may not be able to apply the formula without having many other parameters in place first. I am not sure of what all parameters I must have to derive the time in this case.

    I do not recall the necessary elements needed for the formula.

    I should be able to obtain them. I know the coef of the roadway, the grade of incline, and the distance the vehicle traveled prior to impact. I know the type of vehicle and can get the weight of the vehicle to an approximation.

    Is there a formula, or am I searching for a pipe dream?

    Thanks
     
  7. Nov 2, 2007 #6

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    Ooh, a mystery thriller!

    The grade of just 3 degrees will be negligible, in compared to accelerations produced by cars.

    I also presume the co-eff of friction is that for rolling friction. Otherwise, it’s of no use.

    Assuming constant acceleration, d = (½)at^2. You can get ‘t’ from this, provided you know ‘a’.

    The component of g along the road will be g*(sin 3 deg). The resisting force is 0.7*m*g so the deceleration will be 0.7*g due to friction.

    The other component of acceleration has to be experimentally found. You may also get the maximum acceleration from the car manual, but I can’t see how you will know the actual value.

    If you can figure out roughly the speed at impact, then you can know the accn by using v^2=2da.
     
  8. Nov 2, 2007 #7

    jph

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    Thank you!!

    I appreciate your response. It was very helpful.

    jph
     
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