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2010_term_one_key

# 2010_term_one_key - –2 So in fundamental units P = kg•m...

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SC/BIOL 2090.02 — Current Topics in Biophysics 07 October 2009 T ERM T EST O NE : KEY QUESTION ONE Proportion and Scaling of a 10-fold taller human If a human being were 10 times taller than normal, how thick would the legs have to be to provide the same strength as a human of normal height? The problem has been explored previously in course notes, lecture and assignments. Essentially, compressive strength scales per area, weight scales with volume (V 2/3 is proportional to A). If the human is 10 times taller, mass will be 10 times more, area must be increased 10 3/2 = 31 to maintain the same compressive strength. Other alternatives (compressive h critical and Euler ʼ s column) are awkward at best. [A 3/2 (8/8); partial credit for effort or creativity] QUESTION TWO Physical Meanings What is a Pascal? Remember that Dr. Lew is not a physicist, and he believes that units are important, in addition to your explanation. Apparently, pressure (P) is Force (Newtons) per area (m 2 ) [P = N•m –2 ]. Newtons (N) are kg•m•s

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Unformatted text preview: –2 . So, in fundamental units, P = kg•m –1 •s –2 . [P = N•m –2 (7/8); kg•m –1 •s –2 (1/8); partial credit for effort] QUESTION THREE Reynolds number The fairy fly is reputedly the smallest flying insect. In fact, the feathery appendages can barely be considered wings. How is it that a fairy fly can fly? See Next Page [formula setup (2/8); units (4/8); rational answer (2/8)] Hints: A comparative approach may be most useful, considering the physical environment of a fairy fly compared to that of a normal size bird. You can approximate their relative flight velocities as 2000 body lengths per minute. Terminal velocity may also be helpful, and is defined by: V t = 2 mg " AC d where V t is the terminal velocity, m is the mass, g the acceleration due to gravity (9.81 m/s 2 ), the density of air, A the effective area and C d the drag coefficient (assume it is 24/R e ). SC/BIOL 2090.02 — Current Topics in Biophysics 07 October 2009...
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2010_term_one_key - –2 So in fundamental units P = kg•m...

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