Need help determining speed. CHP is LYING!! Drag racers and math geeks wanted!
12-04-2009, 10:30 AM
#1
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Need help determining speed. CHP is LYING!! Drag racers and math geeks wanted!
So I got pulled over leaving my driveway, I was merging from a center "suicide lane." He thought I was PASSING a car in the middle lane (oh the joys of STi ownership, they always think you are a dumb-racerboy) so.
He says I was doing 75 mph. I know he didn't get me on radar b/c of the conditions. I measured the distance I had to get to speed. 404 feet. which is .076 of a mile. Unless I got the fastst stock STi on the planet I cant do this. So for you drag racers/mathematicians....
How fast would I have been going in a 1/4 mile run with these statistics.
404 feet>>>>>@75 MPH
1320 feet = 1/4 mile 660 feet = 1/8 mile
HELP!!! I cheated in math class, cause I thought I would never need it!
He says I was doing 75 mph. I know he didn't get me on radar b/c of the conditions. I measured the distance I had to get to speed. 404 feet. which is .076 of a mile. Unless I got the fastst stock STi on the planet I cant do this. So for you drag racers/mathematicians....
How fast would I have been going in a 1/4 mile run with these statistics.
404 feet>>>>>@75 MPH
1320 feet = 1/4 mile 660 feet = 1/8 mile
HELP!!! I cheated in math class, cause I thought I would never need it!
12-04-2009, 10:39 AM
#2
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Assuming the acceleration is constant, my calculations come up as follows
404 feet - 75 mph
660 feet - 122.525 mph
1320 feet - 245.05 mph
I don't know of ANY Subaru that can pull a 245 mph quarter mile. That's over twice as fast as a stock 'Vette.
404 feet - 75 mph
660 feet - 122.525 mph
1320 feet - 245.05 mph
I don't know of ANY Subaru that can pull a 245 mph quarter mile. That's over twice as fast as a stock 'Vette.
12-04-2009, 10:40 AM
#4
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Considering a VW bug with a 2180cc motor in it, NA, can do the 1/8th mile at 103mph, I see nothing unbelievable about your sti doing 74 in that distance.
Sounds to me like you got caught "exhibition of speed", I would say pay it, do traffic school to keep it off your record, and be done with it...but I doubt considering your past posts here, that you will listen.
1.53 second stock 60' times, thats well within reason of hitting 75 at 400.
Sounds to me like you got caught "exhibition of speed", I would say pay it, do traffic school to keep it off your record, and be done with it...but I doubt considering your past posts here, that you will listen.
1.53 second stock 60' times, thats well within reason of hitting 75 at 400.
12-04-2009, 10:44 AM
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Considering a VW bug with a 2180cc motor in it, NA, can do the 1/8th mile at 103mph, I see nothing unbelievable about your sti doing 74 in that distance.
Sounds to me like you got caught "exhibition of speed", I would say pay it, do traffic school to keep it off your record, and be done with it...but I doubt considering your past posts here, that you will listen.
1.53 second stock 60' times, thats well within reason of hitting 75 at 400.
Sounds to me like you got caught "exhibition of speed", I would say pay it, do traffic school to keep it off your record, and be done with it...but I doubt considering your past posts here, that you will listen.
1.53 second stock 60' times, thats well within reason of hitting 75 at 400.
12-04-2009, 10:45 AM
#8
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This is going to be really difficult to solve mathematically -- you can't apply a typical position/velocity physics equation because your acceleration is not constant. Here is Torricelli's equation, from Newtonian mechanics, which would help you generate a value for acceleration, but like I mentioned earlier it would apply to the entire period of acceleration which is not the case. Furthermore you are going to then have to prove that the sti isn't capable of such a rate of acceleration.
v_f^2 = v_i^2 + 2 a \Delta d \,
It seems to me like your best argument in court would be to just bring in a google maps print out and show the proximity of your house to the merging lane.
v_f^2 = v_i^2 + 2 a \Delta d \,
It seems to me like your best argument in court would be to just bring in a google maps print out and show the proximity of your house to the merging lane.
Last edited by akdmx; 12-04-2009 at 10:47 AM. Reason: forgot to put the formula in
12-04-2009, 10:49 AM
#10
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thanks AKDMX, I think that equation would go over the judges head. And I don't think I can solve that equation either! 
thanks for the help bruv!
I am not sure, I was looking at the merge not my speedo, but I have test when road was clear, I can get to about 50 mph when pushing.
thanks for the help bruv!I am not sure, I was looking at the merge not my speedo, but I have test when road was clear, I can get to about 50 mph when pushing.
Last edited by horsecut54; 12-04-2009 at 10:51 AM. Reason: adding stuff
12-04-2009, 10:53 AM
#11
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/facepalm
ok, let me help you guys understand this. The acceleration curve is not a linear line, its a long sweeping curve. 1st into 2nd are going to accelerate at x2 the rate as 3rd into 4th, and so on.
So at 60 feet in lets say 2 seconds, your just in the middle of the power band between 2nd and 3rd. Hell even my Camry can get up to 60 in 400 feet, and its a 4cyl slushbox. HOWEVER, at that point it falls on its face, and takes another 60 feet to gain just 5mph. Again its all about the acceleration curve.
404 feet is only 200 feet shy of a 1/8 mile, so are still well within 3rd/4th gear range and pulling in the heavy powerband area. Looking around the net we find that a STOCK STI posts about 100mph on average in the 1/4, even if we assume a smooth acceleration curve, you are looking at a 100' speed of around 50mph +/- 2. Stretch that out to 400 feet, and factor in the curve and again, you are well within reason to be up at 70+/-2 and thats being conservative.
ok, let me help you guys understand this. The acceleration curve is not a linear line, its a long sweeping curve. 1st into 2nd are going to accelerate at x2 the rate as 3rd into 4th, and so on.
So at 60 feet in lets say 2 seconds, your just in the middle of the power band between 2nd and 3rd. Hell even my Camry can get up to 60 in 400 feet, and its a 4cyl slushbox. HOWEVER, at that point it falls on its face, and takes another 60 feet to gain just 5mph. Again its all about the acceleration curve.
404 feet is only 200 feet shy of a 1/8 mile, so are still well within 3rd/4th gear range and pulling in the heavy powerband area. Looking around the net we find that a STOCK STI posts about 100mph on average in the 1/4, even if we assume a smooth acceleration curve, you are looking at a 100' speed of around 50mph +/- 2. Stretch that out to 400 feet, and factor in the curve and again, you are well within reason to be up at 70+/-2 and thats being conservative.
12-04-2009, 10:54 AM
#12
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What was the actual violation on your ticket? You say he couldn't have gotten you on radar - if that's really true then you should be able to contest a speeding violation easily.
If it was reckless driving (for 'passing' in the center divider), then this discussion of speeds, etc is pretty moot since that's a judgment call on the part of the officer. If that's the case, I would contest it in court with a map of your house/driveway and where the incident took place to show that you were using the center lane to merge.
And on the note of speed/acceleration: internal combustion engine vehicles to not accelerate at a constant rate, just look at anyone's dyno plot of torque over RPMs and generalize RPMs as relative time. Torque is simply acceleration multiplied with the lever arm length (technically the cross product, but not relevant here). Unless a torque curve is table-top flat (as in some EVs), the acceleration varies a lot over time. Non-constant acceleration makes the problem very difficult to solve.
Edit: I see some others are also aware of this. Yay for physics!
If it was reckless driving (for 'passing' in the center divider), then this discussion of speeds, etc is pretty moot since that's a judgment call on the part of the officer. If that's the case, I would contest it in court with a map of your house/driveway and where the incident took place to show that you were using the center lane to merge.
And on the note of speed/acceleration: internal combustion engine vehicles to not accelerate at a constant rate, just look at anyone's dyno plot of torque over RPMs and generalize RPMs as relative time. Torque is simply acceleration multiplied with the lever arm length (technically the cross product, but not relevant here). Unless a torque curve is table-top flat (as in some EVs), the acceleration varies a lot over time. Non-constant acceleration makes the problem very difficult to solve.
Edit: I see some others are also aware of this. Yay for physics!
12-04-2009, 10:55 AM
#13
Try having the same thing happen, but on the freeway in moderate traffic, up a moderate grade, in the rain. I couldn't have broken 65mph, that was my last "speeding" ticket from the CHP. *coughquotasPerformanceGoalsquotascough*
Luckily I don't have anything on my record and it'd been 2 years since my last infarction, so I just bit the pillow @ traffic school.
Luckily I don't have anything on my record and it'd been 2 years since my last infarction, so I just bit the pillow @ traffic school.
12-04-2009, 10:56 AM
#14
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Okay, well according to the equation, if you hit 75mph (33.52800 m/s) after traveling 404 feet (123.1392 meters), then you maintained an acceleration of 4.56445 meters/second/second (m/s^2).
12-04-2009, 11:06 AM
#15
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What was the actual violation on your ticket? You say he couldn't have gotten you on radar - if that's really true then you should be able to contest a speeding violation easily.
If it was reckless driving (for 'passing' in the center divider), then this discussion of speeds, etc is pretty moot since that's a judgment call on the part of the officer. If that's the case, I would contest it in court with a map of your house/driveway and where the incident took place to show that you were using the center lane to merge.
And on the note of speed/acceleration: internal combustion engine vehicles to not accelerate at a constant rate, just look at anyone's dyno plot of torque over RPMs and generalize RPMs as relative time. Torque is simply acceleration multiplied with the lever arm length (technically the cross product, but not relevant here). Unless a torque curve is table-top flat (as in some EVs), the acceleration varies a lot over time. Non-constant acceleration makes the problem very difficult to solve.
Edit: I see some others are also aware of this. Yay for physics!
If it was reckless driving (for 'passing' in the center divider), then this discussion of speeds, etc is pretty moot since that's a judgment call on the part of the officer. If that's the case, I would contest it in court with a map of your house/driveway and where the incident took place to show that you were using the center lane to merge.
And on the note of speed/acceleration: internal combustion engine vehicles to not accelerate at a constant rate, just look at anyone's dyno plot of torque over RPMs and generalize RPMs as relative time. Torque is simply acceleration multiplied with the lever arm length (technically the cross product, but not relevant here). Unless a torque curve is table-top flat (as in some EVs), the acceleration varies a lot over time. Non-constant acceleration makes the problem very difficult to solve.
Edit: I see some others are also aware of this. Yay for physics!
I said he didn't get me on radar b/c he said I was doing 75, then worte on the ticket 70, then crossed that out and wrote 65. This whole situation stinks of something bad.