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Can someone check my maths?
turbodisplay - 20/12/09 at 02:24 PM

Assuming no friction and a constant hp engine, a 1000kg car takes :
30 hp to go from 0 - 15mph in a second.

482 hp to go from 0 - 60mph in a second.

I think I`m right just would like to get a second opinion.
Thanks
Darren

[Edited on 20/12/09 by turbodisplay]

matt_claydon - 20/12/09 at 03:17 PM

Kinetic energy = 0.5*m*v^2

60 mph = 26.8 m/s

Therefore KE at 60 mph is:

0.5 * 1000 * 26.8 * 26.8 = 359120 joules

To get that much KE in one second would therefore require a power input of 359120 W, i.e. about 360 kW.

360 kW = ~483 hp.

I assume you did the 15 mph calc the same way. Neglecting friction is rather a big assumption though

[Edited on 20/12/09 by matt_claydon]

clairetoo - 20/12/09 at 03:18 PM

Not sure about your maths , but my 232 bhp drag-bike would go from 0 - 60 in .97 sec - but it only weighed 270 kg (with me sat on it)

So I guess double the power and 4x the weight done quite add up ?

turbodisplay - 20/12/09 at 03:52 PM

Thanks matt, saved my sanity! I used the same calc, but I was having problems reversing the calculation, so wanted to check.

I agree that ignoring friction is very wrong, I will adddress that!
Claire how much did you rev the engine, you can get huge increase in power by storing energy in the flywheel, so the inital hp could be in excess of 1000hp!

Thanks
Darren

clairetoo - 20/12/09 at 04:02 PM

quote:
Originally posted by turbodisplay

Claire how much did you rev the engine, you can get huge increase in power by storing energy in the flywheel, so the inital hp could be in excess of 1000hp!

Thanks
Darren

Bikes dont have a flywheel
In fact , it had a lightened crank and clutch as well as a taller primary drive (to slow down the clutch and gearbox) - it left the line at 8400 , and hit 12800 before hitting second gear (at about 62 mph)

turbodisplay - 20/12/09 at 04:44 PM

As you can see I`m not a bec person!
Obviously there is some rotating mas though.
Thinking about it 4 times less mass, half the power means 0.5 s, with friction 1s sounds right.
Darren

Angel Acevedo - 21/12/09 at 03:05 AM

No friction=No traction.
Spinning on 2 axis!!!
engine wise and wheel wise....

Ninehigh - 23/12/09 at 12:45 AM

True but how would he factor in the friction? For starters what's the drag coefficiency of the vehicle, and then what's the drag of the tyres?

Then is there anything else? Winds, crosswinds.. No doubt there are far too many variables.