# Street help: A car traveling down the street stopped 150 feet after the brakes were applied.About how fast was the car traveling? - Help.com

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## A car traveling down the street stopped 150 feet after the brakes were applied.About how fast was the car traveling?

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what car

what tires

what was the weather like day night time of year

I believe that basic physics and elementary algebra are the tools you need for this.

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to many varibles to give a correct answer

tire wear road con temp of the day
time of year

60 mph = 5,280 fpm = 88 fps.
I would say about 45 mph assuming conditions are good.

I don’t think a proper answer is achievable. Like Just Max said, there are too many variables.

Car weight, ABS vs non ABS, tires, road conditions, weather, amount of force applied to the brake pedal, suspension…

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Take into consideration, guys, “A car traveling down the street stopped 150 feet after the brakes were applied.”

This is an absolute statement. No matter what the conditions were/are, the absolute is: the car stopped 150 feet after the brakes were applied.

To me, conditions and variables would come into question IF it were about stopping the car within the distance of 150 feet.

It leaves a lot to the imagination. I imagine that they could have slammed on the breaks, maximizing deceleration, or maybe they were going 1/2 mile per year and pressed the breaks very lightly.

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*brakes

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Big Al, I disagree.

If we had to identical cars, but car A weighted 1 ton and car B weighted 2 tons, car A would have to be travelling faster than car B. The more mass a car has the harder it is to stop it, since the braking distance is the given value then the speed would vary. This is probably the most important variable, since there is no way around it.

ABS, suspension, road conditions and weather would dictate the efficiency of the braking. Although I agree we could probably leave them out and simply assume the car braked as efficiently as possible (without slipping), there would still be no way around the fact that the mass of the car is missing.

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Yunikat wrote:
Big Al, I disagree.

If we had to identical cars, but car A weighted 1 ton and car B weighted 2 tons, car A would have to be travelling faster than car B. The more mass a car has the harder it is to stop it, since the braking distance is the given value then the speed would vary. This is probably the most important variable, since there is no way around it.

ABS, suspension, road conditions and weather would dictate the efficiency of the braking. Although I agree we could probably leave them out and simply assume the car braked as efficiently as possible (without slipping), there would still be no way around the fact that the mass of the car is missing.

I can see what you’re saying, but the question entails an absolute that requires a bit of reverse formulation.
150 feet is quite a distance, really.

Most average size cars have an average weight of about a ton and a half.
ABS breaks are a federal standard since. . .well - forever.
I think it is both safe and fair to presume optimum conditions in all concerned factors.

mindhealer wrote:
It leaves a lot to the imagination. I imagine that they could have slammed on the breaks, maximizing deceleration, or maybe they were going 1/2 mile per year and pressed the breaks very lightly.

This is funny! !Lol. Actually, this is the only statment that threw me. However, even the best running fuel efficient engine would need gas before the year is over.
:P

Look -
at 60 MPH, you travel 5,280 per minute or 88 feet per second.
If you assume that you can bring the car to a stop within 3 seconds that’s a general distance of 264 feet.
However, in the technical sense, the loss of speed is expodentially less from one second to the next.
It could be that the car is traveling 60MPH.
If I were smater, I’d be able to figure it out - there is an answer.
Investigators are able to determine how fast a vehicle was taveling as it skidded to a crash by measuring the skid marks. There is a formula.

BIG AL ONE wrote:
This is funny! !Lol. Actually, this is the only statment that threw me. However, even the best running fuel efficient engine would need gas before the year is over.
:P

So you’re saying the car ran out of gas and stopped after only a week or two of braking instead of waiting out the whole couple of months that pressing on the brake pedal would have taken to stop the vehicle? If so, I fully agree, but only given the circumstantial evidence we have at hand. If any new evidence shows up I might have to change my opinion.

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Velocity (speed, more or less) is a relative measure. If the car were traveling east, it would be moving faster than if it were moving west, relative to, say the earth’s core. That does not factor in the earth’s own orbital velcity around the sun, or the solar systems velocity, or our galaxy’s, etc.

If the car were traveling 212 MPH, it could have stopped within 150 feet, if there were a good, solid wall at the end of the street. Survival of the occupants, however, would be unlikely.

I think the biggest factor is what sort of urban area the car is in. Some places the traffic is so intense that it doesn’t matter what the laws of physics “technically” are, you are required to bend them to suit local custom.

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BIG AL ONE wrote:
Most average size cars have an average weight of about a ton and a half.
ABS breaks are a federal standard since. . .well - forever.
I think it is both safe and fair to presume optimum conditions in all concerned factors.

Average size cars may have an average weight in the USA, I bet they don’t in the rest of the world. Average size cars where I live, for instance, are a lot less. I owned a “small” car that weighted around 900Kg, my dad’s van is an average size car here and doesn’t reach 1050Kg.

ABS breaks may be federal standard and all cars may be produced with them since X years, but not all ABS cars break equally (nor all cars have ABS brakes). Their deceleration factor puts out even more variables. It would be far easier to assume maximum braking performance possible, yet there would be not only car mass but also deceleration value missing from the equation.

Yes, we can assume optimum conditions, just for the problem’s sake. So with optimum conditions and maximum breaking efficiency (whatever that may be), what would be the deceleration rate of a car?

BIG AL ONE wrote:
Look -
(…)
If you assume that you can bring the car to a stop within 3 seconds that’s a general distance of 264 feet.
However, in the technical sense, the loss of speed is expodentially less from one second to the next.

You cannot assume how much it would take to brink a car to a stop. That’s the thing.

Also, the loss of speed is exponentially *more* from one second to the next. :)

BIG AL ONE wrote:
Look -
If I were smater, I’d be able to figure it out - there is an answer.
Investigators are able to determine how fast a vehicle was taveling as it skidded to a crash by measuring the skid marks. There is a formula.

You’re right, there are *pseudo* formulas, but no agreement in which one should be used. All it takes to vary the breaking distance of a car is to install worse tires and you’ll have a bigger breaking distance. Or increase the weight. Or wet the road a little bit. Or vary break pedal pressure. Or change brake fluids. Or put it tires with less thread. Worse brake pads. Different ABS system. Different distribution of weight on the car itself. Change suspension. Etc, etc etc.

Investigators are *NOT* able to determine how fast a vehicle was travelling by it skids. They make an educated guess, but it is a guess. As soon as I know (and googled), there is absolutely no way to calculate stopping time of a car with the variables provided by the OP, and no possible educated guess.

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I would like to hope that the OP’s question is based on a homework assignment.
And would be kind enough to reply to his/her own post.

BIG AL ONE wrote:
Look -However, in the technical sense, the loss of speed is expodentially less from one second to the next.

Yunikat wrote:
- the loss of speed is exponentially *more* from one second to the next. :)

Yes - thank you for the technical correction. I’m sometimes gramatically challenged. The terms and conditions of “loss” was meant to be a single factor.

BIG AL ONE wrote:
I would like to hope that the OP’s question is based on a homework assignment.
And would be kind enough to reply to his/her own post.

Well I was hoping the OP would provide a little more info though. Don’t get me wrong, I still am wondering how one would go about estimating the braking distance (or initial speed in this case). After you brought up that insurance investigators do it I got myself curious on how they make the educated estimation. After all, in some cases that may mean the difference between someone being blamed of an accident or innocent.

A quick google search did show up some of those formulas but the math is way beyond me. Maybe you could solve them? Also, I’m wondering if they still do it nowadays; modern vehicles don’t skid a lot. Any ideas?

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Yunikat wrote:
- modern vehicles don’t skid a lot. Any ideas?

You would be right. Todays vehicles don’t skid (in direct forward motion) too much.
This is because of the “advances in ABS technology.” The ABS (antilock brake system), releases the tires before they can lock up.

That was ans always be a load of crappola. I remember the days BEFORE ABS. If I want to lock up my tires to their maximum extreme it should happen and be there.

But the driving of today is not the same as it was yesterday, it’s sofer and more delicate (don’t go too fast now). Because if you do, you can forget any real stopping power, the accident is eminant. ABS will fail you every time.

The data of yesterday concludes that speed was the primary cause of mosst accident in conclusionary reports, thus, we must slow society down.
Goodbye 70’s muscle cars. :’(

Funny you mention that, I don’t like today’s cars either. Today’s cars create bad drivers, in my opinion. Not only they isolate the driver from the world too much with their tomb silence, there isn’t any real feedback from the road nor any true signs that the car is on its limit. Unfortunately I’m not old enough to have known those older cars, but as a young guy I still prefer buying older mechanical cars.

On top of that, with all the “security” features that save drivers from mistakes only make the drivers push beyond the physical limits of the car and the day the computer fails… We have an upside down car and a wall that used to be there.

ABS is somewhat helpful (since most people tend to slam their brakes and lock their wheels) but it also seems to fail whenever people need it the most. Either way, it’s not that hard to learn braking properly.

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BIG AL ONE wrote:

Yunikat wrote:
- modern vehicles don’t skid a lot. Any ideas?

The data of yesterday concludes that speed was the primary cause of mosst accident in conclusionary reports, thus, we must slow society down.
Goodbye 70’s muscle cars. :’(

Sorry for the double post, forgot this paragraph.

Funny thing is, supposedly today’s cars are safer, and they are able to push their limits a lot more more “safer” than older cars (with all the computer assistance). They do brake faster too. However, despite being “safer”, speed limits stayed to same, yet they crash a lot more.

To me, the more sissier the cars, the dumbest the drivers.

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Yunikat wrote:
To me, the more sissier the cars, the dumbest the drivers.

A fair conclusion. because there is a severe lack of respet for the tin can.
When you’re behind the wheel of 700 horses or more, the fear of what the machine is commands respect from the driver as well as others on the road.

BIG AL ONE wrote:

Yunikat wrote:
To me, the more sissier the cars, the dumbest the drivers.

A fair conclusion. because there is a severe lack of respet for the tin can.
When you’re behind the wheel of 700 horses or more, the fear of what the machine is commands respect from the driver as well as others on the road.

I meant sissier in the aspect of driver assist, but I do agree that when one fears what’s under the hood respects cars a lot more. I wouldn’t last a couple of hours with the foot over 700hp though. It’s just too much for me!

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