## Energy Assignment II

- What releases more heat: combustion of 10 grams of coal or 10 grams of gasoline? (1 point)

- If 1-kg of methane (CH
_{4}) is burned every second, how much “thermal power” is available? (2 points) - How many BTUs of heat energy are needed to raise the temperature of 12 gallons of water from 50
^{0}F to 130^{0}F? (2 points)

- What is the efficiency of an engine that has 3000 J of heat added during combustion and loses 2200 J of heat in the exhaust? (2 points)

- What is the change in electric potential energy when 3 Coulomb charge flows from 55 Volts to 40 Volts? Is this a gain or loss of energy? (2 points)

- A light bulb draws a current of 2 Amps when connected to a wall outlet (120 Volts). What is the resistance and wattage of the bulb? (3 points)
- A household circuit at 120 V is fused for 20 A. How many 100-Watt light bulbs can be simultaneously used in this circuit? (2 points)

- Suppose a family of four is considering purchasing a solar electric device for their home. Annually, they currently consume ~ 10,000 kWh of electricity and pay $0.1/kWh. Assume a 2.5 kW solar electric device operates perfectly for 4,000 hours a year and costs $15,000 (installed). Approximately how many years will it take to break even on this investment without any incentives or rebates? (3 points)
- Suppose you have a total of five (5) “vampire loads” in your house, each of which requires 10 W of power as long as they are plugged in (examples of “vampire loads” are cell phone chargers and plasma TV’s on standby – always on, often in dark corners, sucking electric power). If operated every day for one year, calculate the annual cost of electricity to power these loads if charged $0.2/kWh. (3 points)

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