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Example 9-6

Example 9-6 - driving at the minimum...

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Example 9-6 A Flywheel-Powered Car Context-Rich You are driving an experimental hybrid vehicle that is designed for use in stop-and-go traffic. In a  car with conventional brakes, each time you brake to a stop the kinetic energy is dissipated as  heat. In this hybrid vehicle, the braking mechanism transforms the translational kinetic energy of  the vehicle’s motion into the rotational kinetic energy of a massive flywheel. As the car returns to  cruising speed, this energy is transferred back into the translational kinetic energy of the car. The  100-kg flywheel is a hollow cylinder with an inner radius  R 1  of 25.0 cm, an outer radius  R 2  of 40.0  cm, and a maximum angular speed of 30,000 rev/min. On a dark and dreary night, the car runs  out of gas 15.0 mi from home with the flywheel spinning at maximum speed. Is there sufficient  energy stored in the flywheel for you and your nervous grandmother to make it home? (When 
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Unformatted text preview: driving at the minimum highway speed of 40.0 mi/h, air drag and rolling friction dissipate energy at 10.0 kW.) PICTURE The kinetic energy is calculated directly from. SOLVE 1. The kinetic energy of rotation is Answer: 2. Calculate the moment of inertia of the hollow cylinder using an expression from Table 9-1 : Answer: 3. Convert to rad/s: ω Answer: 4. Substitute these values to find the kinetic energy: Answer: 5. Energy is dissipated at 10 kW at a speed of 40 mi/h. To find the energy dissipated during the 15-mi trip, we first need to find the time required for the trip: Answer: 6. The energy is dissipated at 10 kW for 1350 s. The total energy dissipated is Answer: 7. Is there enough energy stored in the flywheel? Answer:...
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Example 9-6 - driving at the minimum...

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