speedyxjs
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| posted on 20/3/09 at 10:47 AM |
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Science assignment help
I have just a couple of questions left and my brain wont work.
How do you calculate the braking efficiency of a car when all you have is the speed before braking, the deceleraction and the distance taken to stop?
How long can i resist the temptation to drop a V8 in?
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omega0684
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| posted on 20/3/09 at 10:55 AM |
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im a Virology man, sorry, different kinda science, lol, sorry no help what so ever! 
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001Ben
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| posted on 20/3/09 at 11:16 AM |
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I don't know if it will help but try here
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hughpinder
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| posted on 20/3/09 at 11:19 AM |
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calc deceleration from v = u -2as
v = 0 (stopped)
u = initial speed m/s
s = stopping distance in meters.
Efficiency depends on what braking is maximal - if its 1g, efficiency in percent
= ( a(from above) *100) / 9.81
Regards
Hugh
Added: That link that appeared just before my post is better!
[Edited on 20/3/09 by hughpinder]
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tegwin
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| posted on 20/3/09 at 11:19 AM |
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You have enough information there to work out the power dissapation required by the brakes to stop the car...
Id be buggered if I can remeber the formulas though... Pretty sure you need to work out the mass of the car and then take it from there!
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www.verticalhorizonsmedia.tv
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matt_gsxr
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| posted on 20/3/09 at 11:29 AM |
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dear mr Hugh
v = u - 2 as
is wrong.
just look at the units!!!
v.v = u.u - 2 a s
where in this case v = 0.
so
a = v*v / ( 2 * s)
This will yield "a" or the acceleration.
I'm not sure what you mean by efficiency. You could convert to braking force.
F = m a (Force = mass * acceleration) can be rerranged to tell you the force that you are decellerating with.
Note on units:
m in kg
v in m/s (1 m/s = 2.16mph, so to get speed in m/s divide mph by 2.16)
Matt
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Dangle_kt
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| posted on 20/3/09 at 11:32 AM |
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Eh?
Hasn't this forum got an english lanaguage only rule?
Sounds like a load of voodoo to me!
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02GF74
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| posted on 20/3/09 at 12:16 PM |
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quote:
Originally posted by speedyxjs
How do you calculate the braking efficiency of a car when all you have is the speed before braking, the deceleraction and the distance taken to stop?
It is Friday aftefnoon so I ain't gonna think to hard about this but I don't think you can. As ^^^ say, you almost certainly would need
to know mass of car.
I also don't think you need distance taken to stop since you have deceleration.
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hughpinder
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| posted on 20/3/09 at 01:12 PM |
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Matt
I am ashamed. Must think more carefully.
The 'braking efficiency' thing was in the original post.
Thanks
Hugh
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mr henderson
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| posted on 20/3/09 at 02:03 PM |
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Excuse me chaps, aren't we all (except me  ) forgetting something?
We're not in a newtonian 'body with no forces acting on it' situation here, we are in a car whcih would slow down quite quickly if
the engine was turned off situation.
Air resistance, the tyres and other sources of friction all need to be considered. If one knew how long the car would take to stop if the engine was
turned off but the brakes were not applied then we would be in a good position to start calculating the brake efficiency for when they
are applied
John
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Tinks1
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| posted on 20/3/09 at 03:36 PM |
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if V=0 then surely
U*U = 2as
a = U*U/2s
[Edited on 20/3/09 by Tinks1]
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