Energy Transformations Review

1. Energy TransformationsReview SPH4C – April 2010

2. True/False • The efficiency of an energy transformation is the ratio of the input energy to the useful output energy. • Two identical elevators travel from the ground floor to the penthouse of a building. One is loaded with passengers and the other is empty. Both elevators arrive at the same time. Therefore, they are operating with the same power.

3. True/False • Two energy transformations have efficiencies of 40% and 60%. The overall efficiency of the two energy transformations operating together is 24%. • A 1.0-MW generating station produces as much energy in one day as two 100-kW generating stations produce in five days.

4. True/False • Diesel engines require high-efficiency spark plugs because the fuel-air mixture is less highly compressed than in a gasoline engine. • The unit of work is the joule, which is equivalent to a newton-metre.

5. True/False • For an ideal extension spring, the force applied to the spring increases directly as the stretch increases. • The type of heat transfer that does not require any particles is called radiation.

6. True/False • Power is a scalar quantity measured in watts. • As the time interval required to perform a given amount of work increases, the power increases. • When expressed as a percentage, an efficiency of 0.55 is 55%.

7. True/False • Electric motors tend to have much lower efficiencies than gasoline motors. • In a four-stroke gasoline engine, the spark jumps across the gap in the compression stroke.

8. True/False • The overall efficiency of an energy-transformation technology is generally lower than the efficiency of only one energy transformation.

9. Multiple Choice Which of the following energy-transformation equations best describes the operation of a wind generator that is used to power an electric can opener? • thermal energy -> electrical energy -> kinetic energy • wind energy -> thermal energy -> kinetic energy • kinetic energy -> electrical energy -> kinetic energy • electrical energy -> kinetic energy -> thermal energy

10. Multiple Choice Which type of energy is most commonly a part of energy transformations? • electrical energy • chemical potential energy • kinetic energy • thermal energy

11. Multiple Choice The energy-transformation equationgravitational potential energy -> kinetic energy -> gravitational potential energycould represent which of the following events? • a roller coaster gliding up and over a hill • an arrow shot into the air • a bouncing ball • a car accelerating along a level road

12. Multiple Choice Work is • energy transferred to an object • energy transferred from an object • the product of force and distance • all of the above

13. Multiple Choice In which of the following cases is no work being done? • a child pushes against a wall that does not move • a child pulls a wagon across a horizontal surface • a child pulls a wagon up a hill • a wagon runs down a hill on its own

14. Multiple Choice Work is measured in joules when force and distance are respectively measured in • newtons and centimetres • kilograms and centimetres • grams and metres • newtons and metres

15. Multiple Choice How much work is done by a person who exerts a force of 8.0 N to push a 2.0-kg object horizontally over a distance of 3.0 m? • 48 J c) 16 J • 24 J d)12 J

16. Multiple Choice How far does a 5.0-N force have to move a 2.0-kg object to accomplish 24 J of work? • 4.8 m c) 2.4 m • 3.4 m d) 0.42 m

17. Multiple Choice How much energy is required to do 8.0 J of work? • exactly 8.0 J • much less than 8.0 J • much more than 8.0 J • slightly more than 8.0 J

18. Multiple Choice Using the force-displacement graph, determine the work done to move the object 100 cm. • 1.0 x 103 J • 20.0 J • 10.0 J • d)0.20 J

19. Multiple Choice A 25-g pen rolls off a desk onto the floor 60 cm below. Which of the following statements is true? • The pen gains 0.15 J of gravitational potential energy in the fall. • The pen loses 0.15 J of gravitational potential energy in the fall. • The pen gains 1.5 J of gravitational potential energy in the fall. • The pen loses 1.5 J of gravitational potential energy in the fall.

20. Multiple Choice A 62-g ball is dropped from the roof of a building 16 m above the ground. Neglecting air resistance, what is the ball’s speed upon landing? • 18 m/s c) 8.9 m/s • 13 m/s d) 5.7 m/s

21. Multiple Choice Which of the following would not be considered an advantage of CANDU nuclear reactors? • emissions to the atmosphere are low • Canada has considerable reserves of high quality uranium • CANDU reactors have impressive safety records • CANDU reactors are relatively inexpensive to build and operate

22. Multiple Choice Which of the following would not be considered to be renewable? • solar • wind • biomass • nuclear

23. Multiple Choice Which combination of light bulbs and operating times would consume the same quantity of energy as six 100-W light bulbs operating for 1.0 h? • either 60-W light bulbs operating for 1.0 h • ten 50-W light bulbs operating for 1.2 h • two 150-W light bulbs operating for 2.5 h • one 300-W light bulb operating for 1.8 h

24. Multiple Choice What is the proper sequence of a four-stroke engine following the intake stroke? • compression, exhaust, power • power, compression, exhaust • compression, power, exhaust • power, exhaust, compression