3.7 Practice Questions PDF

3.7 Practice Directions: Show your work and include units. Use GRASS to do these questions. 1. Calculate the power of a drill which transfers 2000 J of energy in 5 seconds. Show your answer in watts and kilowatts. Remember: 1000 W = 1 kW 2. A runner transforms 3500 J of energy in 5 minutes. What i...

3.7 Practice Directions: Show your work and include units. Use GRASS to do these questions. 1. Calculate the power of a drill which transfers 2000 J of energy in 5 seconds. Show your answer in watts and kilowatts. Remember: 1000 W = 1 kW 2. A runner transforms 3500 J of energy in 5 minutes. What is the runner’s power? Express your answer in watts and kilowatts. 3. How much energy was released from the battery in a 2 W flashlight that was switched on for 4.5 hours? 4. A microwave oven operates on 1500 W of power and is used for 20 minutes. How much electrical energy, in joules, is used by the microwave oven? 5. What is the efficiency of a toaster that converts 2000 J of electrical energy into 200 J of useful heat energy? 6. A light bulb takes in 30 J of energy per second. It transfers 3 J as useful light energy and 27 J as heat energy. Calculate the efficiency. 7. A kettle takes in 2000 J of energy per second. It transfers 1500J as useful heat energy and 500J is wasted as sound energy. Calculate the efficiency of the kettle. 8. A refrigerator operates on average for 12 hours a day. If the power rating of the fridge is 600 W, how much electrical energy does the fridge use in one week in joules? 9. A 750 Watt hairdryer is used for 15 minutes. a. Calculate the electrical energy used in Joules and in Kilojoules b. Calculate the cost to use 15 min. every day for 1 year @ 8 cents/kw▪h 10. A room has a 60 watt, a 100 watt, and a 150 watt light bulb. How much does it cost to use all of the lamps for 2.5 hr @ 8 cents/ kW▪h? 11. An electric heater draws 1100 W of power. Electricity costs 8¢ per kW h. How much does it cost to operate the heater 3.0 h a day for 30 days? 12. Bob has an electric lawn mower which transfers 5kW▪h of energy. The cost of energy is 10 cents/kW▪h. Calculate the total cost of running his lawn mower for 1 hour. 13. Ingrid’s washing machine has a power of 2kW. She uses it for 2 hours. Each kW▪h costs her 5 cents. a. First calculate the energy used by the washing machine. b. Now calculate the total cost of running the washing machine.