UNIT 5: WORK and ENERGY RECORD ALL ANSWERS ON ANSWER SHEET.

Transcription

1 PHYSICAL SCIENCE UNIT 5: WORK and ENERGY RECORD ALL ANSWERS ON ANSWER SHEET. name 1. Which of the following processes requires the most work? a. A 10 kg weight rests on a table. b. A person holds a 1 kg weight still with outstretched arms. c. A person lifts a 1 kg weight 1 m off the floor. d. A 10 kg ball is rolled across the floor at a constant speed for a distance of 10 m. 2. A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate moves a distance of 4.0 m, how much work does the man perform? a. 165 N c. zero b. 220 N d. 145 J 3. What are the units of power? a. watts c. joules per second b. horsepower d. All of the above 4. Which of the following statements about work and energy is not true? a. When work is done, energy is transferred or transformed. b. Energy may be defined as the ability to do work. c. Work and energy are always equal. d. Work and energy have the same units. 5. Gravitational potential energy depends on a. the mass of the object. c. the acceleration due to gravity. b. the height of the object. d. All of the above 6. A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy? a. 100 J b. 2,000 J c. 10 J d. 500 J 7. The kind of energy associated with atomic bonds is a. nuclear energy. c. chemical energy. b. light energy. d. kinetic energy. 8. A pendulum swings back and forth and has a kinetic energy of 400 J at a particular point in its path. Which of the following statements is not true? a. Both the kinetic and potential energy are decreasing. b. The minimum kinetic energy is zero. c. When the kinetic energy is zero, the potential energy will be 400 J greater. d. The potential energy increases when the kinetic energy decreases. 9. The brakes on a car exert a frictional force of 6,000 N in getting the car to stop. If the work done by the brakes is 120,000 J in coming to a stop, how many meters does the car travel after the driver applies the brakes? a. 6 m c. 12 m b. 20 m d. 40 m

2 10. An object has a kinetic energy of 810 J after falling a certain distance. If the mass of the object is 20 kg, what is the speed of the object at this time? a. 10 m/s c. 8 m/s b. 9 m/s d. 7 m/s 11. The transfer of energy as heat caused by the collision of molecules is called a. convection. c. contact. b. conduction. d. radiation. 12. The type of energy transfer that takes place between objects in direct contact is a. conduction. c. contraction. b. convection. d. radiation. 13. A type of energy transfer that can take place in empty space is a. convection. c. conduction. b. contraction. d. radiation. 14. Energy from the sun reaches Earth by a. conduction and radiation. c. conduction and convection. b. radiation only. d. conduction only. 15. Heat can a. Keep things warm b. Do work c. Make engines run d. All of the above 16. A material that reduces the flow of heat by conduction, convection, and radiation is. a. a conductor c. an insulator b. condensation d. a solar collector 17. The transfer of energy that does NOT require matter is. a. combustion c. conduction b. radiation d. convection 18. Energy from the Sun travels to Earth as. a. chemical energy c. radiant energy b. combustion d. mechanical energy 19. Which process is taking place in all three pictures? a. Conduction c. Specific heat b. Radiation d. Convection

3 20. Which statement about the figure above is true? a. Pot A has a higher temperature than Pot B. b. Pot B has a higher temperature than Pot A. c. Pot A has more heat energy than Pot B. d. Pot B has more heat energy than Pot A. 21. A material made of would be a very good conductor of energy. a. air. c. wood. b. liquid. d. metal Temperature is a measure of the average energy of an object s particles. a. mechanical c. potential b. kinetic d. light Which of the following is the name of a temperature scale? a. Celsius c. Kelvin b. Fahrenheit d. All of the above 24. The temperature at which all molecular motion tops is a. 0 C. c. 0 K. b. 0 F. d. All of the above 25. Which of the following temperatures is impossible to measure? a. 85 F c. 20 K b. 50 C d. 545 F 26. What is the mechanical advantage of a single, fixed pulley? a. 0.5 c. 2 b. 1 d A dropped racquetball will not return to its original position because a. potential energy is inefficient. b. the mechanical energy is stored up for later bounces. c. some of the mechanical energy is converted to nonmechanical energy. d. energy is not conserved 28. Which of the following phrases describes a situation in which potential energy is not changes into kinetic energy? a. an apple falling from a tree c. the string of a bow being pulled back b. a dart being shot from a spring-loaded gun d. a creek flowing downstream

4 MATCHING 1. A. Absolute zero B. Insulator C. Specific heat D. Conductor E. Temperature F. Expansion joint G. Calorimeter H. Heat The measure of the average kinetic energy of a substance; a measure of how hot or cold something is. A measure of the energy of a substance based on the temperature and amount of the substance. Thermal energy that flows from something at a higher temperature to something at a lower temperature. Temperature not attainable on Earth; the temperature at which particles come to a complete stop; 0 0 K or C Used on bridges and roads to compensate for thermal expansion of the concrete. A material that is a poor conductor of energy. (transfers energy poorly) Examples include wood and Styrofoam. A device used to measure the heat (specific heat) of a substance 7. A material that is a good conductor of energy. (materials through which heat can move easily) Particles are close together. Examples include most metals. MATCHING 2. Match each term with one of the descriptions below. a. power d. potential energy g. kinetic energy b. compound machine e. energy h. law of conservation of energy c. efficiency f. power 1. Work output of a machine divided by the work input; can never be greater than 100% (According to the video shown in class, a car s is about 20%) 2. the energy due to motion; depends on both mass and velocity 3. The rate at which work is done; measured in watts; P = W/t 4. Device made up of more than one simple machine; Examples include scissors, bicycles, wheelbarrow 5. States that energy can neither be created no destroyed by ordinary means; needs to be considered in the context of open and closed systems; the total amount of energy in the universe never changes, although energy may change from one form to another. 6. the energy of an object due to its position, shape, or condition; stored energy 7. The capacity to do work; exists in many forms; measured in joules

5 MATCHING 3 Match each simple machine with its set of examples. A. Simple lever B. Pulley C. Wheel and axle D. Inclined Plane E. Wedge F. Screw 1. 2.,

6 Kinetic vs. Potential Energy This graph shows a ball rolling from A to G. Use the graph above to answer the following Which letter shows the ball when it has maximum kinetic energy? Which letter shows the ball when it has maximum potential energy? Which letter shows the ball when it has the least potential energy? Which letter shows the ball when it has the least kinetic energy? 5. Which letter shows the ball when it has just a little more kinetic energy than A? 6. Which letter shows the ball when it has just a little more potential energy than letter C? 7. Which letter shows the ball when it has just a little less potential energy than letter F? 8. Which letter shows the ball when it has just a little more kinetic energy than letter G? 9. Which letter shows the ball when it has just a little less kinetic energy than letter D? 10. Which letter shows the ball when it has just a little less potential energy than letter C? Which sequence shows an increase in potential energy? A. E, F, B, G B. B, F, E, C C. D, E, B, F D. A, G, F, C Which sequence shows an increase in kinetic energy? A. E, F, B, G B. B, F, E, C C. D, E, B, F D. A, G, F, C

7 IDENTIFY/DRAW (Do this on your answer sheet!) Draw arrows in each picture to show the direction in which heat moves. PROBLEMS REQUIRING WORK. 1. A boy exerts an average force of 65 N when he lifts a box 1.2 meters. How much work does he do? a. 0 J b. 54 J c. 66 J d. 78 J 2. How much power is required to do 180 J of work in 2.4 s? a. 7.5 W b. 75 W c. 178 W d. 430 W Calculate the gravitational potential energy relative to the ground when an 82 kg person climbs to the top of a 2.0 m stepladder. a. 164 J b. 3.3 x 10 2 J c. 402 J d. 1.6 x 10 3 J A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy? a. 100 J b. 2,000 J c. 10 J d. 500 J A dog running at a speed of 12 m/s has 1,080 J of kinetic energy. What is the mass of the dog? a. 7.5 kg b. 15 kg c. 30 kg d. 45 kg

8 COMPLETION Complete each statement. Use the word bank below. A. convection B. conductor C. thermometer D. radiation E. conduction F. heat 1. In Figure 6-1, thermal energy is transferred to the sunbather in room B primarily by. 2. In Figure 6-1, most of the heat provided by the fireplace in room C goes up the chimney and is therefore transferred by. Figure In Figure 6-1, the thermal energy of the iron in room D is transferred to the clothes by. 4. In Figure 6-1, room A, the heat from the pot on the stove moves to the pot's handle by. 5. A(n) is a device for measuring temperature. 6. The energy transferred between the particles of two objects because of the temperature difference between the two objects is called. 7. The transfer of energy by the movement of fluids with different temperatures is called. 8. A(n) is a material through which energy can be easily transferred as heat

9 NGA 1. 2.

10 3. All carts shown below are identical 0.5 kilogram metal carts. Blocks are placed in the carts have a mass of 1 kilogram each. Which cart arrangement has the greatest amount of gravitational potential energy with the cart sitting at the top of the ramp as shown in each diagram? 4. The picture below shows the different positions of a skier as she is lifted to the top of a slope and then skis down the other side. Which statement best explains the change in the skier s potential energy? A. The skier loses potential energy as she is lifted up the slope and loses potential energy as she skis down the slope. B. The skier gains potential energy as she is lifter up the slope and maintains the same potential energy as she skis down the slope. C. The skier gains potential energy as she is lifted up the slope and loses potential energy as she skis down the slope. D. The skier loses potential energy as she is lifted up the slope and gains potential energy as she skis down the slope.

11 5. At what time does the box have the greatest kinetic energy? A s B s C s D s 6. Where is the potential energy of the box the greatest? A. The potential energy is constant throughout the motion. B. The potential energy is greatest at the top of the incline. C. The potential energy is greatest midway along the incline. D. The potential energy is greatest at the bottom of the incline 7. Jackie uses a portable electric drill to remove screws from a broken wooden table. He noticed that the screws holding the table together were warm to the touch after being removed from the wood. What explains this phenomenon? A. Mechanical energy from the drill was converted into thermal energy due to friction. B. Electrical energy from the drill was converted into chemical energy due to resistance. C. Thermal energy form the drill was converted into mechanical energy due to inertia. D. The process of removing the screw concentrated the thermal energy that was already present in the wood.

12 8. Using a jack, Sonia is able to raise a 15,000-newton (N) car off the ground with a force of 500N. What is the mechanical advantage of the jack? a. 2 b. 10 c. 15 d The efficiency of a machine is a measure of how much of the work put into a machine is converted to useful output work by the machine. What causes the efficiency of a machine to be always less than one? a. friction b. poor design c. limited strength of the user d. elastic limit of the parts 10. The graph shows the length and input force for the four inclined planes pictured above. A reasonable Hypothesis based on these data is that as the length of the inclined plane decreases,. a. the amount of work decreases b. the mechanical advantage increases c. the input force required decreases d. the input force required increases

13 11. Which of the diagrams shows a lever being used to do work? a. b. c. d.

14 PHYSICAL SCIENCE UNIT 5 TEST: name WORK and ENERGY ANSWER SHEET MATCHING 1 MATCHING 2 MATCHING 3 KE vs. PE IDENTIFY/DRAW COMPLETION NGA

15 PROBLEMS REQUIRING WORK