
#1
Nov107, 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 



#2
Nov207, 05:07 AM

HW Helper
P: 1,986

Is this a homework question? In that case, you write what you have done so far.




#3
Nov207, 05:28 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 38,882

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.




#4
Nov207, 06:16 AM

HW Helper
P: 1,986

Formula for time to distance from stop
I think the vehicle is simply rolling downhill. Let the OP present the problem clearly.




#5
Nov207, 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 



#6
Nov207, 11:28 AM

HW Helper
P: 1,986

Ooh, a mystery thriller!
The grade of just 3 degrees will be negligible, in compared to accelerations produced by cars. I also presume the coeff 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. 



#7
Nov207, 12:32 PM

P: 3

I appreciate your response. It was very helpful.
jph 


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