need help from someone who is good in physics

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kranzx

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theoretically, how much power (in bhp or kW) it takes to accelerate 960kg of mass from 0-60mph (or 0 - 100km/h) in 4.8 secs? let's just ignore all aerodynamics, drags, tyre friction, engine efficiency and such.

many thanks.
 
Energy is 1/2 m v^2, works out to 370.9 kJ. Divide that by 4.8 seconds gives you 77.3kW, or 104 horsepower.

That's if you are putting out the same power all the time though, with an internal combustion engine you are probably going to need a peak power output quite a bit higher than that since you won't be at peak power all the time plus you've got wheelspin and such to worry about.
 
To get a more realistic answer, you should try fooling around with different numbers in CarTest.

Because I'm bored, I'll go do that myself and see if I can't get you an answer.

Edit: I can't. It seems Windows XP refuses to run that old DOS program, and the Windows version is shareware. :indiff:
 
retsmah: thanks a lot, but i think i really have to take more factors into consideration to get a clearer picture.

Wolfe2x7: i'll give it a try. looks very good though. thanks a lot.
 
You can pretty accurately calculate acceleration of a vehicle, if you know a bit about it. At school last year we pretty quickly put together a simulation of our Formula car's acceleration to figure out what kind of gearing we wanted to run, it worked well enough to win the acceleration event at this years Formula SAE west competition. All you need is a torque or power curve, gearing, and tire break-away torque, and you can pretty acurately simulate what a 0-60 run is going to be like.

You won't really be able to accurately say how much power you need for a 4.8 second run. The power an engine puts out is a curve, a function of rpm, it's not a single number. You can probably get pretty close if you know the displacement of the motor, and can guess at what the power or torque curves look like.

If you happen to be interested in physics, it's a good, relativeley easy problem to work out. Which is uncommon in vehicle dynamics, most stuff relating to car performance is very difficult to calculate.
 
My math c (top math's in qld, australia for those who don't know what math c is) assignment is based on this stuff. Although its more graphing oscilatting motion, eg. suspension.
 
130bhp my answer comes straight from a lotus elise though.
 
That Lotus Elise has 190 HP though, at least in the US. And thats the one that accelerates that fast last I checked.

Like retsmah said, its an easy problem the way you put it, in reality, its a tad bit more annoying. Whats harder of course is predicting grip levels corner and such I think.

BTW, retsmah, I'll likely be at the next SAE event with WSU, if my life permits time :p
 
Yes, 190hp with 710kg pulls 4.7 - the 130HP version is in the late 5's or early 6's.
 
kranzx
theoretically, how much power (in bhp or kW) it takes to accelerate 960kg of mass from 0-60mph (or 0 - 100km/h) in 4.8 secs? let's just ignore all aerodynamics, drags, tyre friction, engine efficiency and such.

many thanks.
Click to expand...

Surely the underlined passage takes it out of the context of a car completely? And if it didn't, you need to ask whether it's FWD or RWD (or 4WD).

In no context at all, to push a mass of 960kg from rest to 60mph (96km/h - or 26.8m/s) in 4.8s:

Power = average speed * acceleration * mass

Average speed is start speed (0m/s) plus finish speed (26.8m/s), divided by two = 13.4m/s
Acceleration is finish speed (26.8m/s) minus start speed (0m/s), divided by time (4.8s) = 5.6m/s/s
Mass = 960kg

Power = 13.4m/s * 5.6m/s/s * 960kg
= 71,913.4W = 71.9kW

If you fancy converting kW to horsepower, that's 96.4hp. But remember, that's taking this as the instruction:

kranzx
let's just ignore all aerodynamics, drags, tyre friction, engine efficiency and such.
Click to expand...
 
Can you calculate it including those peramaters Famine?
 
No.

Not unless I had them. And even then... no.


Thing is, a 190hp car doesn't HAVE 190hp. It has 190hp @ n,nnn rpm. Over the rest of the range it doesn't have anywhere near 190hp. But we also know that at n,nnn rpm, excluding clutch slip, it's doing nn mph. You can't just peg it at 190hp, launch it and reach 60mph without varying the revs.

To work out a given vehicle's acceleration you really need the torque curve (ignore the engine power curve - it's a function of the engine torque curve anyway), the external temperature/humidity/height above sea level, the gearing in each gear (and final drive), the drivetrain efficiency curve, the wheel/tyre size (rolling radius - tyre footprint isn't terribly relevant), the current weight - and so on and so forth. It's mind-bogglingly nuts.

You can do a pretty bang-up job (within a couple of tenths) with the wheel torque curve and mass on their own - the rest is just fluff for making it accurate.
 
it's all started when someone made a bold claim of doing 4.8secs. the body is an 1.3L hatchback which is only 960kg. although the 1.8 model weight over 1100kg. engine is lifted from a VR4-RS with 240bhp on papers (as well as ECU, gearbox). i'm sure that car isn't 960kg anymore but i just wanted to know whether it is possible to achieve 4.8secs. we invited him to one of our gathering to settle it once and for all, only to find out he actually doomed his ride in year 2002.

 
kranzx
it's all started when someone made a bold claim of doing 4.8secs. the body is an 1.3L hatchback which is only 960kg. although the 1.8 model weight over 1100kg. engine is lifted from a VR4-RS with 240bhp on papers (as well as ECU, gearbox). i'm sure that car isn't 960kg anymore but i just wanted to know whether it is possible to achieve 4.8secs. we invited him to one of our gathering to settle it once and for all, only to find out he actually doomed his ride in year 2002.

Click to expand...

Short answer? No.

Sub-5s from FWD is extremely hard.
 
Did you ever get that DOS program to work for you, kranzx? That takes care of all of the calculation problems Famine mentioned, of course.

Theoretically, with that 240hp engine and a curb weight of about 1100kg, the power-to-weight ratio could be enough to do 4.8...but that's stretching it a bit, especially with the FWD, as Famine mentioned.
 
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