exam 1 problems

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Pennsylvania State University *

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102

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Mechanical Engineering

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Dec 6, 2023

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An 80-watt incandescent light bulb is operated for 101 hours, and a 14 watt LED light bulb is operated for the same period of time. At 0.06 dollars per kWh, what is the cost savings (units of $) of the LED bulb? Answer to two decimal places, do not include unit symbols. Correct! Correct Answer 0.4 margin of error +/- 5% Energy = Power x duration. For example, 100W x 120h = 12,000Wh = 12 kWh, and 15W x 120h =1,800 Wh = 1.8 kWh Energy savings is the difference (12-1.8) kWh = 10.2 kWh; at the rate of 10 cents per kWh this amounts to $1.02 WATCH CONVERSIONS A 150-watt electric warming blanket is operated for 10 hours per day during the winter, and winter lasts 105 days per year. At 0.09 dollars per kWh, what is the cost of the energy consumed by the electric blanket (dollars) each year? Answer to two decimal places, do not include unit symbols. Correct Answer 14.17 margin of error +/- 1% The electric blanket cost depends on the price and the consumed energy, and the consumed energy is derived from the power rate and working hours. For example, kWh x hr / day x day / y x $/kWh = $ / y. The renewable energy consumption in a place is 6 billion BTUs, while the nonrenewable energy consumption is 13 billion BTUs. After one year, the renewable energy consumption increased by19 %, while the nonrenewable energy consumption increased by 7 %. What is the new ratio of renewable energy to nonrenewable energy? Answer to two decimal places, do not include unit symbols. You Answered Correct Answer 0.51 margin of error +/- 5% To get the answer, you need to calculate the new renewable energy consumption and nonrenewable energy consumption first. The flame temperature in an automobile engine is 1,019 °C, and the exhaust is emitted at 58 °C. What is the Carnot efficiency of the engine? (Answer units: %) You Answered Correct Answer 74.37 margin of error +/- 2

Use the Carnot efficiency formula and be sure to convert the temperatures to Kelvin for the formula. Please refer to section 3.7: The Carnot Efficiency. The useful output from a heat engine is 227 cal. The energy that is wasted is 5,915 J. What is the Carnot efficiency of the engine? (Answer with units of %. i.e. 30 not 0.3. you do not need to provide the %) Correct! Correct Answer 13.8 margin of error +/- 1 Efficiency = ((useful energy output) / (useful energy output + waste energy output))*100. Note: Use units consistently. Please refer the section of the Efficiency of Energy Conversion Devices. If the energy input of a system is 81 calories and its output is 49 calories, what is the efficiency of the system? (Answer units: %, i.e. 30 not 0.3, do not include the %) Correct! Correct Answer 60.5 margin of error +/- 1 System Efficiency = (useful energy output) / (total energy input) * 100. Please refer to section: Efficiency of Energy Conversion Devices. The following step efficiencies apply to the use of gasoline in a car: Crude production: 91.3%, Refining 87.2%, Transportation 89.2%, Engine efficiency 27%. What is the total efficiency of the process? (Answer units: %, i.e. input 10 not 0.1. Be sure to exclude the % as Canvas does not accept symbols) Correct! Correct Answer 19.2 margin of error +/- 1 Overall Efficiency of a system is the product of step efficiencies. Please refer to section 3.9: Calculating Overall Efficiency. The Carnot efficiency of the automobile engine is 53%, and the flame temperature is 517 ℃ , what is the exhaust temperature ( ℃ )? Answer to two decimal places, do not include unit symbols. You Answered Correct Answer 98.22 margin of error +/- 3 Use the Carnot efficiency formula and temperatures in Kelvin.

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