Re: [Phys-l] real-world problem

[brian whatcott <betwys1@sbcglobal.net>]

On 2/1/2011 1:08 PM, Paul Lulai wrote:
> A source for interesting / fun problems that aren't necessarily physics problems.
> Car Talk Puzzlers.  I haven't found a great way to implement them into my class, but they are fun.  I am starting to post these questions and the TPT Physics Question of the month for my students as extra credit options.  I don't yet feel comfortable requiring a certain number of these problems to be solved in the course of a quarter.  I might move in that direction once I have a better feeling for how my students do with them.
> <  http://www.cartalk.com/content/puzzler/>
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> Paul Lulai
The answer to a puzzle they asked two weeks ago would be helpful to 
pre-calculus students.

The question:
How can I find the quarter full mark using a dipstick in a [horizontal 
axis] cylindrical fuel  tank as fitted to a truck?

The answer:
Cut a circle from card.
Draw a diameter, and a perpendicular radius.

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Cut a semicircle out on the diameter line.
Balance the semicircle on the radius line with a pencil tip for the pivot.
This is the centroid of the shape, and represents the center of mass of 
a similar cylinder - this is about 40% of the radial distance from the 
center.

A stick marked with three lines scaled to the diameter of the fuel tank 
in question
therefore  fits the purpose.   A mark at 70% of the diametrical length,  
one at 50% of the diameter,  and one at 30% of the diameter.

Brian W