helpz me

[tris-]

sorry to cross post or what ever its called these days. but i just realised there is a lot of car nuts in here.

for anyone in the know, could you possibly tell me how you can determine at what speed a cars wheels will lock, or if thats even possible. as ive been posed the following question -

"1 Determine the minimum stopping distances at all speeds up to the cars maximum when the cars wheels lock and the car skids to a halt on the road for the following conditions"

maybe im reading it wrong. imo its stating the cars wheels will lock at maximum speed, but then again i could be wrong.

 

[Kryten]

think you're reading it wrong : it is assuming that you're travelling at said maximum speed and stamped on the brakes - which in a vehicle with no ABS would simply lock the wheels. question is a shit one bearing in mind ABS though...

 

[tris-]

kryten, i believe ABS is not a factor at all. go as far as to pretend that ABS does not even exist. i think im reading it wrong too, so its good to know someone else agrees

 

[Kryten]

aye - if this is a mathematical (mechanical maths) question ignore all the car things and just assume you're dealing with something weighing nearly 2 tonnes taking into account the friction from that weight and the 4 bits of rubber on the road

 

[tris-]

aye, it is maths i am doing. basically i need to build a model in excel to calculate stopping distances upto the maximum speed of two different cars. that is simple enough for me, its the maths im shite at. although i did re arrange a formula to work out friction coefficients and i was pretty chuffed with that.

i cannot work out if that question is saying "work out the coefficients then determine if the wheels are locked, and also show the stopping distance" or if its saying to use the coefficients made available to us for 3 different road types. which show static and kinetic ones. now afaik, if its a kinetic coefficient then the wheels have locked. so it maybe that the question is saying "use the kinetic coefficients for the three road types to work out the stopping distances".

 

[Gumbo]

It's a horribly flawed question in the real world, but I can see how it might almost work as a maths question. If you make some enormous and plain wrong assumptions.

 

[Trem]

Agreed, there is so many different answers to the same questions.

Depends how quick the reactions are, depends how quick and how hard you press the pedal, depends on what type of brakes and car is involved etc.

Stupid stoodent question

 

[Damini]

It's a basic physics question, badly phrased. You have to assume the wheels are locked and braking is instantly applied so that you can then factor the mew and speed into the formula (spinning wheels and human variables would screw this formula up).

Up to the maximum is giving you the range of speeds for which to find this value, so I guess it's asking you for either a formula to work this out with the speed given as x, or asking you to draw a graph to plot these values.

 

[Damini]

Basically:

Assume the wheels aren't turning.

Assume braking is instant.

The car is travelling at (range 0 to maximum velocity) on a surface that has a mew of (input different road surfaces values) : what are the stopping distances within this range.

 

[tris-]

im glad im not the only one thinking it was shittly worded. the point is not for it to be realistic or anything of that nature. ok sure it uses real physics theories and all that jazz. but the point of the exercise was to recieve a problem then plan and design a solution to it.

that isnt the only question we have to answer.

thanks for das inputs.