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Fluid fag-chanics

Name: ANONYFUCKED 2009-09-14 16:33

sup textboardians,

I have a problem with an assignment (in b4 do your homework yourself), and want a nudge in the right direction. It's in a 'fluid mechanics' unit, but I swear it's not related to the current lectures. The questions was originally in norwegian (don't fucking ask) so I ran it through google translate and corrected a bit of grammar but it's still poorly worded i think.

"A bicycle rider who weighs 90kg including the bike, crosses a finish line with constant speed. At this time,the cyclist is exerting 290W and it can be assumed that all the effects will take to overcome air resistance. The Cyclists front surface area is 0.35m2, the air density is 1.2kg/m3 and (motsandskoeffisienten?) can be set at Cd = 0.9.

a) What speed is the cyclist travelling as he passes the finish line?

After finishing the race, the cyclist straightens up so that the front surface area is doubled. From now on, he let the bike drop at a horizontal distance and the bike slows due to the air resistance

b) How long does it take from finishing the race until the speed is halved"

The lecturer is talking about mach numbers and compressible flows right now, and I have no fukken idea how that could be related. Any help lads?

Name: Anonymous 2009-09-14 17:43

motsandskoeffisienten?
Cd would be the drag coefficient.
The lecturer is talking about mach numbers and compressible flows right now, and I have no fukken idea how that could be related.
Sounds like it isn't - this should be a pretty simple application of the drag equation.
See if anything at http://en.wikipedia.org/wiki/Drag_(physics) looks familiar.

Name: Anonymous 2009-09-14 17:52

ahh right so still dimensional analysis I suppose. hrrmmm. and no idea what the fuck motsandskoeffisienten means, norwegian mumbojumbo. (yep taking a class in norwegian and don't speak any).

Name: Anonymous 2009-09-15 5:13

Not sure how to go about part b) ...

any help?

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