SPH 4C Energy Transformations

SPH 4C Energy Transformations Review

1. What is work? What is energy? What is the formula for calculating work? What are the units for work and energy?

2. Name 6 different types of energy and an example of a source of that energy. Ex. Sound (source = speaker)

3. An engineer uses a single car to test the roller coaster track, shown in Fig. B. In answering the following questions, assume that friction can be ignored and the speed at A is O. In each case, give a reason for your answer. (a) Where is the gravitational potential energy the greatest? (b) Where is the kinetic energy the greatest? (c) Where is the speed the greatest? Fig. B (d) Give a written description of what happens to the speed of the car as it rolls from A to B and so on to E.

4. A 30 kg box is held 5.0 m above the ground. How much gravitational potential energy

does it possess? If it is lowered to 2.0 m above the ground, how much Eg was lost? (1470 J; 882 J)

5. A 0.025 kg bullet traveling at 245 m/s hits a tree. How much kinetic energy does the bullet impart on the tree? (750 J)

6. What does the law of Conservation of Energy have to say about a falling rock?  Epg will turn into Ek

7. Why is energy never truly conserved in a mechanical system?  “lost” to heat and sound; inefficiencies in the system

8. Dr. Boom sends his 3.5 kg monkey straight up with a velocity of 24.0 m/s. How high will the monkey go before it comes to a complete stop? (29.4 m)

9. A 40 g spring with a constant of 24 N/m is stretched by 30 cm. If it is let go, and no energy is lost, how high will the spring go? (2.76 m)

10. A ball of mass 2 kg has a starting velocity of 7.0 m/s at the bottom of a ramp. It only reaches a height of 2.0 m. a) Calculate the total energy of the ball at the bottom of the ramp. (49 J) b) Calculate the gravitational potential energy of the ball at the top of the ramp. (39.2 J) c) How much energy did the ball lose? (9.8 J) d) Where did lost the energy go? (friction = heat, sound)

\sph4C\energy\071dc57b6f49ebe344c34770d8db2fe2.doc e) Calculate the efficiency of the ramp. (80%)

11. Write the energy transformation equation (diagram) for using a slingshot. Kinetic Energy Elastic Potential Energy Kinetic Energy

12. Explain why it is impossible to have a motor that is 100% efficient.  Some E is always lost to heat and sound in moving parts, due to friction

13. When thermal energy is transferred, when does it stop?  When the temperatures of the two substances are equal

14. Why is the inside of an astronaut’s suit made from highly reflective material? From what form of heat transfer is this protecting the astronaut?  Reflects radiation from leaving when there is no sun; reflects sun’s radiation when the astronaut is exposed to the sun

15. Describe each of the thermal energy transfer methods and give an example.  Conduction – BBQ grill on meat  Convection – warm air in a room rises to the top floor, and cold air sinks to the basement  Radiation – Sun’s energy warms the Earth

16. Give examples of thermal energy loss in the home, and the type of transfer they are.  Conduction – heat leaves through the door, the glass and also the walls  Convection – warm air rises through to the attic; drafts leak out of the poor seals in windows and doors  Radiation – Infra Red can leave through windows

17. How can we protect against heat loss (give 3 examples)? Which type of transfer does each insulation method prevent?  Fiberglass insulation in the attic – convection  Double glazed windows – convection and conduction  Fill wall sockets with foam (behind drywall) – convection and conduction  Reflective blinds / curtains - radiation

18. A thermos is a good device for maintaining a liquid’s temperature. What methods of insulation does it use?  Double-wall vacuum seal  Hollow plastic top; Rubber/plastic seal between cap and bottle  Reflective interior

19. Sketch an energy flow diagram illustrating the efficiency of a car engine if 100% is input from fuel, 5% is lost to air as sound, 4% is lost to the road as heat, and 70% is lost from the engine as heat.

Chemical Car Engine Kinetic E of Car Potential E of 21% Fuel 100%

Wasted heat & sound 20. Sketch an energy flow / path diagram for a propane barbecue. 79%

\sph4C\energy\071dc57b6f49ebe344c34770d8db2fe2.doc Chemical Barbecue Thermal Energy Potential E of Propane

Wasted heat & sound

21. If the average cost of electricity during mid-peak time of use is $0.089/kWh, how much does it cost to run a 60 W lightbulb for 3 hours a night for a week? ($0.112)

22. Which are the most efficient types of light bulb in the home today? Which are the least efficient?  CFL (compact fluorescent); halogens

23. a) Where is most of your electricity used in the home? (heating appliances: water heater, dryer, stove, A/C) b) How can you as an individual reduce how much energy you use / waste in your home? (turn lights off; reduce temperature of house and water supply; stop heat loss leakage)

24. In energy conservation, no energy is actually “lost”. Where, then, does the lost energy go? (turns into other forms of “unwanted” energy)

25. The specific heat capacity of water is 4200 J/(kgC). The specific heat capacity of aluminum is 900 J/(kgC). If 2 kg of each substance had its temperature raised by 20 C, how much energy would be needed in total? (2.04 x 105 J)

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