Math Is Fun Forum

joobimaths

Member

Registered: 2008-05-10

Posts: 1

Need Answers Please

If jims radius bicycle wheel does 1000 revoloutions on a trip which takes 12minutes what is jims average speed?

Please Help

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Need Answers Please

What is the radius of the bicycle wheel?

The wheel travels a horizontal distance of 2πr when it makes one revolution, where r is its radius. Thus, in 1000 revolutions, it travels a horizontal distance of 2000πr. If r is in kilometres, the average speed of Jim’s bicycle is then 2000πr ÷ 0.2 [∵ 12 min = 0.2 hr] = 10 000πr kilometres per hour.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Need Answers Please

Trust Jane, she is right!

Also:
  Speed = 1000 turns per 12 minutes = 1000/12 turns per minute
 
1000 ÷ 12 = 83 and 1/3 turns in a minute.

Now multiply 83 and 1/3 by π
to get how many wheel heights
there are in a minute, if you
pretend the height of the wheel
goes curvy around.  (262)

And then multiply that height thing
by 2 to get how many half-heights
of the wheel go around curvy in
a minute. (524)

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igloo myrtilles fourmis

SvenBee

Member

Registered: 2008-03-08

Posts: 106

Re: Need Answers Please

More of the same I guess: a wheel travels 2πr per revolution.  and average speed is d/t, where d is distance traveled and t is time. So if your distance is 1000 revolutions and you're time is 12 minutes, then your speed is (2000πr)/12. Hope this adds something >.<

-- yeah, for some reason my pi symbol comes up like this π so... yea

Last edited by SvenBee (2008-05-12 03:09:09)

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e...the red-headed stepchild of math.

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Need Answers Please

That's because you're using the one on the row of useful symbols: π
More recently, a bunch of "math smilies" got added, and the other pi is one of those.

In the same way that = , π = π.

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Why did the vector cross the road?
It wanted to be normal.