P2207_fall10_lecture16 - 27 km/h ? P(54 km/h)/P(27 km/h) =...

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Today: Work done by friction, springs Compound bows Power
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A pig has a choice of three different frictionless slides as shown. With which slide will the pig reach the ground with the greatest speed? (Think about the work done on the pig by the pig's weight.) A. (a) B. (b) C. (c) D. all the same
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A toy gun has a spring with spring constant k =100 N/m . The spring is compressed a distance of 10 cm and a ball of mass m =10 g is inserted in the gun. After the trigger releases the spring, what will be the ball's speed v when the spring has returned to its equilibrium length? v=? A. 1 m/s B. 5 m/s C. 10 m/s D. 50 m/s E. none of the above
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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
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Unformatted text preview: 27 km/h ? P(54 km/h)/P(27 km/h) = ? A. 1 B. 2 C. 4 D. 8 E. 16 Power and Energy in Cycling Assume P cyclist Drag force velocity (P = Dv) P cyclist = 1/2 C A v 2 v = 1/2 C A v 3 Assume C~ 0.4, = 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: 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)...
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This note was uploaded on 10/27/2010 for the course PHYS 2207 at Cornell University (Engineering School).

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P2207_fall10_lecture16 - 27 km/h ? P(54 km/h)/P(27 km/h) =...

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