lecture17_notes

# lecture17_notes - A cyclist travels along a flat road at...

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A cyclist travels along a flat road at constant speed v. The power produced by the cyclist all goes to overcoming air drag . How does the power the cyclist must produce to travel at 54 km/h compare with that required to travel at 27 km/h ? P(54 km/h)/P(27 km/h) = ? A. 1 B. 2 C. 4 D. 8 E. 16

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Power and Energy in Cycling Assume P cyclist Drag force × velocity (P = Dv) P cyclist = 1/2 C ρ A v 2 × v = 1/2 C ρ A v 3 Assume C~ 0.4, r = 1.2 kg/m 3 , A~0.7 m 2 Assume human body ~ 25% efficient in converting food energy into mechanical energy. 1 Cal =4.2 J, 1 food Calorie =1 kCal = 4,200 J
Prof. Liepe: v ~ 8 m/s (17 mi/h) P ~ 86 W (~0.12 hp) Burns ~ 344 W, 1.24 MJ/hour, 295 kCal/hour Professional distance cyclist: v ~ 14 m/s (~30 mi/h) P ~ 460 W (~0.6 hp) Burns ~1.8 kW, 6.6 MJ/hour, 1580 kCal/hour Professional sprint cyclist:

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Unformatted text preview: v ~ 20 m/s (~45 mi/h) P ~ 1340 W (~1.8 hp) Burns ~ 5.4 kW, 19 MJ/hour, 4600 kCal/hour Average daily food energy intake for Tour de France Cyclists: ~10,000 kCal/ day (~7 lb of uncooked pasta) Which of the following forces are conservative forces? A. Gravity B. Spring force C. Friction D. two of the above E. three of the above A mass m is connected to a rigid massless rod of length L . The mass is released from the vertical as shown. What is its speed v at the bottom of its motion? m +y L v = ? A. gL B. (gL) 1/2 C. (2gL) 1/2 D. (4gL) 1/2 A block of mass m is released from the top of the frictionless track shown. What is its speed v at the top of the loop-the-loop? R h v = ? A. 2gh B. (2gR) 1/2 C. [2g(h-R)] 1/2 D. [2g(h-2R)] 1/2...
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