Energy use in daily life Transitional Reasoning Download PDF

Questions

1. 1.

   A home-entertainment center draws 150 W of electrical power during active use and is operated for 4 hours each day. For the remaining 20 hours of each day, it remains plugged in on standby mode, drawing a steady power of 20 W. Over a 30-day billing period, how much electrical energy does the system consume in standby mode, and what is the total electrical energy consumed by the system?

   • A) Standby energy: 6.0 kWh; Total energy: 24.0 kWh
   • B) Standby energy: 12.0 kWh; Total energy: 30.0 kWh
   • C) Standby energy: 14.4 kWh; Total energy: 32.4 kWh
   • D) Standby energy: 18.0 kWh; Total energy: 30.0 kWh
2. 2.

   An electric car consumes an average of 18 kWh of electrical energy per 100 km driven. A commuter drives this vehicle 50 km each day and recharges the battery at home using a dedicated 2.5 kW charging point that operates with an overall charging efficiency of 90%. How much electrical energy is drawn from the home grid to replenish this daily commute, and how long does the charging session take?

   • A) 9.0 kWh of electrical energy drawn from the grid, requiring a charging time of 3.6 hours
   • B) 10.0 kWh of electrical energy drawn from the grid, requiring a charging time of 4.0 hours
   • C) 10.0 kWh of electrical energy drawn from the grid, requiring a charging time of 3.6 hours
   • D) 8.1 kWh of electrical energy drawn from the grid, requiring a charging time of 3.24 hours
3. 3.

   A commuter rides an electric scooter along a flat street for a distance of 3000 m in 600 s at a constant speed. During this trip, a constant resistive force of 60 N opposes the scooter's forward motion, and the electric motor consumes 240 kJ of electrical energy from the battery. What are the average electrical power drawn from the battery and the overall energy efficiency of the scooter during this trip?

   • A) The average electrical power drawn is 300 W, and the efficiency is 60%.
   • B) The average electrical power drawn is 400 W, and the efficiency is 75%.
   • C) The average electrical power drawn is 400 W, and the efficiency is 60%.
   • D) The average electrical power drawn is 300 W, and the efficiency is 75%.
4. 4.

   A residential solar-plus-storage system delivers 10.0 kWh of electrical energy from rooftop photovoltaic panels to charge a domestic battery during the day. The battery and inverter system operates with a round-trip energy efficiency of 80%, with the remaining energy dissipated as thermal energy to the surroundings. In the evening, the household draws a steady electrical power of 1.6 kW from the battery to run essential appliances until the stored usable energy is exhausted. Based on this information, what is the total useful electrical energy delivered to the household, and for how long can these appliances operate continuously?

   • A) 2.0 kWh of useful energy is delivered, allowing the appliances to operate for 1.25 hours.
   • B) 12.5 kWh of useful energy is delivered, allowing the appliances to operate for 7.81 hours.
   • C) 10.0 kWh of useful energy is delivered, allowing the appliances to operate for 6.25 hours.
   • D) 8.0 kWh of useful energy is delivered, allowing the appliances to operate for 5.00 hours.
5. 5.

   A portable electric space heater with a rated power of 1500 W is controlled by an internal thermostat to maintain a steady room temperature. During operation, the heating element switches on for 18 minutes and off for 12 minutes in each 30-minute interval. Over a continuous 5-hour period of use, which statement correctly gives the total electrical energy consumed and the heater's average power demand?

   • A) Total energy consumed is 7.5 kWh, and average power demand is 1500 W.
   • B) Total energy consumed is 4.5 kWh, and average power demand is 900 W.
   • C) Total energy consumed is 4.5 kWh, and average power demand is 1500 W.
   • D) Total energy consumed is 3.0 kWh, and average power demand is 600 W.
6. 6.

   A washing machine uses an electric motor rated at 200 W to tumble clothes and an electric heating element to heat the wash water. In a standard hot-wash cycle, the heating element consumes 1.8 kWh of electrical energy while the motor operates for 1.0 hour. In an eco-wash cycle at a lower temperature, the heating element consumes only 0.6 kWh, but the motor runs for 2.0 hours to achieve equivalent cleaning performance. Which statement correctly compares the total electrical energy consumed by the two wash cycles?

   • A) The eco-wash cycle consumes more total electrical energy because doubling the motor's operating duration requires more additional energy than what is saved on water heating.
   • B) Both wash cycles consume an identical total electrical energy of 2.0 kWh because the energy saved by heating the water less is completely cancelled by the extra hour of motor operation.
   • C) The standard cycle consumes 3.8 kWh while the eco-wash cycle consumes 2.6 kWh because a 200 W motor adds 2.0 kWh of electrical energy for every hour it operates.
   • D) The standard cycle consumes 2.0 kWh while the eco-wash cycle consumes 1.0 kWh because the energy saved by heating less water far exceeds the small amount of additional energy used to run the motor longer.
7. 7.

   A homeowner replaces four 60 W incandescent bulbs with four 9 W LED bulbs that provide the same useful light output due to their higher energy efficiency. All four bulbs are turned on together for an average of 5 hours each day. If electrical energy costs $0.20 per kilowatt-hour (kWh), how much electrical energy is saved over a 30-day month, and what is the corresponding reduction in the electricity bill?

   • A) 1.02 kWh and $0.20
   • B) 7.65 kWh and $1.53
   • C) 36.0 kWh and $7.20
   • D) 30.6 kWh and $6.12
8. 8.

   To fill an overhead domestic water tank, a pump must deliver exactly 720 kJ of useful mechanical work to lift the water. A homeowner considers Pump A, rated at 800 W with an efficiency of 50%, and Pump B, rated at 1000 W with an efficiency of 80%. Which statement correctly compares the operation time and the total electrical energy consumed by the two pumps to complete this task?

   • A) Pump B operates for 15 minutes less time and consumes 540 kJ less electrical energy than Pump A.
   • B) Pump B operates for 15 minutes less time but consumes 360 kJ more electrical energy than Pump A.
   • C) Pump B operates for 10 minutes less time and consumes 540 kJ less electrical energy than Pump A.
   • D) Pump B operates for 10 minutes less time but consumes 360 kJ more electrical energy than Pump A.
9. 9.

   An electric kettle with a power rating of 2000 W takes 240 seconds to bring a sample of water to its boiling point, which requires 360 kJ of useful thermal energy. The remaining energy supplied to the kettle is lost as heat to the surrounding air and the kettle body. Which statement correctly evaluates the total electrical energy consumed and the overall energy efficiency of the kettle during this operation?

   • A) The kettle consumes 360 kJ of electrical energy and operates at an energy efficiency of 100%.
   • B) The kettle consumes 480 kJ of electrical energy and operates at an energy efficiency of 25%.
   • C) The kettle consumes 600 kJ of electrical energy and operates at an energy efficiency of 60%.
   • D) The kettle consumes 480 kJ of electrical energy and operates at an energy efficiency of 75%.
10. 10.

    A household operates a 1200 W microwave oven for 30 minutes each day and a 200 W television for 5 hours each day. A resident assumes that the microwave oven must contribute more to the monthly electricity bill because of its significantly higher power rating. Considering a 30-day billing month, which comparison correctly evaluates the total electrical energy consumed by these two appliances?

    • A) The television consumes more energy, using 12 kWh more than the microwave oven.
    • B) The microwave oven consumes more energy, using 12 kWh more than the television.
    • C) The television consumes more energy, using 24 kWh more than the microwave oven.
    • D) The microwave oven consumes more energy, using 18 kWh more than the television.