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Formula for time to distance from stop

by jph
Tags: distance, formula, stop, time
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jph
#1
Nov1-07, 06:39 PM
P: 3
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
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Shooting Star
#2
Nov2-07, 05:07 AM
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P: 1,982
Is this a homework question? In that case, you write what you have done so far.
HallsofIvy
#3
Nov2-07, 05:28 AM
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PF Gold
P: 39,345
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.

Shooting Star
#4
Nov2-07, 06:16 AM
HW Helper
P: 1,982
Formula for time to distance from stop

I think the vehicle is simply rolling downhill. Let the OP present the problem clearly.
jph
#5
Nov2-07, 10:49 AM
P: 3
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
Shooting Star
#6
Nov2-07, 11:28 AM
HW Helper
P: 1,982
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.
jph
#7
Nov2-07, 12:32 PM
P: 3
I appreciate your response. It was very helpful.

jph


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