Re: [Phys-l] Student Misconceptions

["Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>]

Average speed = Distance/time

As defined in most textbooks, which I presume would be precursor material to asking the question.

 Which implies a unique answer to your question provided reasonable assumptions such as "return the same way" means retracing your path on the way home that you took originally.

I.e. avg speed = (2x)/{(x/60)+(x/30)}= 60*60/90 = 40 mph

Where x equal the one-way distance (the delta odometer reading)

I use this as an example of follow what the definitions tell when performing a calculation; rather than jumping to intuition.



> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of Robert Cohen
> Sent: Thursday, September 29, 2011 5:15 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] Student Misconceptions
>
> - - - - -
> Anthony Lapinski wrote:
> <snip>
> If you drive somewhere with an average speed of 60 mph and return the
> same way with an average speed of 30 mph, then is your average speed
> for
> the entire trip less than, equal to, or more than 45 mph?
> <snip>
> - - - - -
>
> Average over time or over space?
>
> Robert A. Cohen, Department of Physics, East Stroudsburg University
> 570.422.3428   rcohen@esu.edu    http://www.esu.edu/~bbq
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