Slide 1 / 113 Slide 2 / 113 8th Grade Energy of Objects in Motion Classwork-Homework 2015-08-25 www.njctl.org Slide 3 / 113 Classwork #1: Energy
1 Define Energy. Slide 4 / 113 2 What two things are necessary for work to be done on an object? Slide 5 / 113 3 How can you determine the amount of work done on an object? Slide 6 / 113
4 What would happen to an object s velocity if positive work was done on an object? Slide 7 / 113 5 Based on the diagram below, is positive or negative work being done on the object? Explain. Slide 8 / 113 6 Based on the graph below, is positive or negative work being done on the object? Explain. Slide 9 / 113
7 A ball is dropped from the roof of the building. The ball initially had 100 J of energy. Just as it landed, it had 90 J or energy. a. How much work was done on the ball as it fell? b. What did the work? Slide 10 / 113 8 What are the two major forms of energy? Slide 11 / 113 9 What is the definition of mechanical energy? Slide 12 / 113
10 What is the definition of non-mechanical energy? Slide 13 / 113 Slide 14 / 113 Homework: Energy 11 What would happen to an object s velocity if no work was done on the object? Slide 15 / 113
12 Based on the diagram below, is the person s speed increasing or decreasing due to air resistance. Explain in terms of work being done on the person. Slide 16 / 113 13 At what time on the graph below does the object start to experience negative work being done on it? Explain. Slide 17 / 113 14 An adult is driving a car which has 50 J of energy. At the end of the drive, the car still had 50 J of energy. How much work was done on the car during the drive? Slide 18 / 113
15 What are the two forms of mechanical energy? Slide 19 / 113 16 Name two examples of non-mechanical energy. Slide 20 / 113 Slide 21 / 113 Classwork #2: Kinetic Energy
17 What two factors does kinetic energy depend upon? Slide 22 / 113 18 If an object is accelerating, how does its kinetic energy change? Justify your answer. Slide 23 / 113 19 If a mouse and an elephant have the same kinetic energy, can you determine which one is running faster? Explain. Slide 24 / 113
20 If an object s speed is doubled, how does its kinetic energy change? Slide 25 / 113 21 If the mass of an object is doubled, how does its kinetic energy change? Slide 26 / 113 22 How much kinetic energy does an 80 kg man have while running at 3 m/s? Show your work. Slide 27 / 113
23 A 6 kg object has a speed of 20 m/s. What is its kinetic energy? Show your work. Slide 28 / 113 24 A 1000 kg car s velocity increases from 5 m/s to 10 m/s. What is the change it the car s kinetic energy? Show your work. Slide 29 / 113 25 What is the SI unit for kinetic energy? Slide 30 / 113
Slide 31 / 113 Homework: Kinetic Energy 26 When is the only time that an object has no k inetic energy? Slide 32 / 113 27 If an object is decelerating, how does its kinetic energy change? Slide 33 / 113
28 How can a more massive object have the same kinetic energy as a less massive object? Slide 34 / 113 29 If an object s speed is cut in half, how does its kinetic energy change? Slide 35 / 113 30 If the mass of an object is cut in half, how does its kinetic energy change? Slide 36 / 113
31 How much kinetic energy does a 4 kg cat have while running at 9 m/s? Show your work. Slide 37 / 113 32 A 2 kg watermelon is dropped from a roof and has a speed of 5 m/s just before it hits the ground. How much kinetic energy does the watermelon have at this moment? Show your work. Slide 38 / 113 33 A 700 kg horse is running with a velocity of 5 m/s. How much larger is the horse s kinetic energy compared to a 100 kg man running at the same speed? Slide 39 / 113
Slide 40 / 113 Classwork #3: Gravitational Potential Energy 34 What three factors does gravitational potential energy depend upon? Slide 41 / 113 35 If an object is thrown up in the air, how does its gravitational potential energy change? Explain. Slide 42 / 113
36 If an object is falling, how does its gravitational potential energy change? Explain. Slide 43 / 113 37 How does your gravitational potential energy change if you are placed on the moon where gravity is lower than on Earth? Slide 44 / 113 38 If the mass of an object is cut in half, how does its gravitational potential energy change? Slide 45 / 113
39 A 1 kg ball is thrown up in the air and reaches a height of 5 m. What is its gravitational potential energy at that moment? Show your work. Slide 46 / 113 40 A 200 kg boulder is sitting on top of a 10 m high hill. What is the boulder s gravitational potential energy? Show your work. Slide 47 / 113 41 What is the gravitational potential energy of a 450 kg car at the top of a 25 m parking garage? Show your work. Slide 48 / 113
42 A 2.0 kg toy falls from 2 m to 1 m. What is the change in GPE? Show your work. Slide 49 / 113 43 A small, 3 kg weight is moved from a height of 5 m to a height of 8 m. What is the change in potential energy? Show your work. Slide 50 / 113 Slide 51 / 113 Homework: Gravitational Potential Energy
44 When is the only time that an object has no gravitational potential energy? Slide 52 / 113 45 How does your gravitational potential energy change if you are placed on Jupiter where gravity is larger than on Earth? Slide 53 / 113 46 If the mass of an object is doubled, how does its gravitational potential energy change? Slide 54 / 113
47 What is the SI unit for gravitational potential energy? Slide 55 / 113 48 A 75 kg skydiver is spotted at a height of 1000 m above the Earth s surface. How much gravitational potential energy does the skydiver possess? Show your work. Slide 56 / 113 49 A placekicker in football is attempting a field goal and kicks a 0.75 kg football. The football hits the crossbar that is 3.1 m tall. How much gravitational potential energy does the ball have when it hits the crossbar? Show your work. Slide 57 / 113
50 The Green Monster is the name for the left field wall at Fenway Park and is 11.33 m tall. How much gravitational potential energy does a 0.2 kg baseball have when it just clears the wall? Show your work. Slide 58 / 113 51 An 80 kg person falls 60 m off of a waterfall. What is her change in GPE? Show your work. Slide 59 / 113 52 A 0.25 kg book falls off a 2 m shelf on to a 0.5 m chair. What was the change in GPE? Show your work. Slide 60 / 113
Slide 61 / 113 Classwork #4: Elastic Potential Energy 53 What two factors does elastic potential energy depend upon? Slide 62 / 113 54 Define the term spring constant? Slide 63 / 113
55 The same spring is stretched by 1 meter and then compressed by 1 meter. In which case will the spring have more elastic potential energy stored in it? Explain. Slide 64 / 113 56 Two identical springs are stretched. Spring A is stretched 1 meter while spring B is stretched 2 meters. Which spring will have more elastic potential energy stored in it? Explain. Slide 65 / 113 57 If a spring is stretched three times as far, by what factor does its elastic potential energy change? Does it increase or decrease? Slide 66 / 113
58 A spring with a spring constant of 500 N/m is stretched 1 meter in length. How much elastic potential energy does the spring have stored in it? Show your work. Slide 67 / 113 59 A spring with a spring constant of 250 N/m is stretched 0.5 meters. How much elastic potential energy does the spring have stored in it? Show your work. Slide 68 / 113 60 A spring with a spring constant of 100 N/m is compressed by 0.25 meters. How much elastic potential energy does it have stored in it? Show your work. Slide 69 / 113
Slide 70 / 113 Homework: Elastic Potential Energy 61 What is meant when a spring has a "relaxed" length? Slide 71 / 113 62 Two springs are stretched to the same distance. If spring A has a spring constant of 200 N/m and spring B has a spring constant of 400 N/m, which spring has more elastic potential energy stored in it? Explain. Slide 72 / 113
63 A spring with a spring constant of 100 N/m is not stretched. How much elastic potential energy does the spring have stored in it? Slide 73 / 113 64 A spring with a spring constant of 200 N/m is stretched 1 meter in length. How much elastic potential energy does the spring have stored in it? Show your work. Slide 74 / 113 65 A spring with a spring constant of 500 N/m is compressed 0.5 meters. How much elastic potential energy does the spring have stored in it? Show your work. Slide 75 / 113
66 A rubber band with a spring constant of 150 N/m is stretched by 0.25 meters. How much elastic potential energy does it have stored in it? Show your work. Slide 76 / 113 Slide 77 / 113 Classwork #5: Conservation of Energy Slide 78 / 113 Questions 67-71 refer to the diagram below, which shows a block starting from rest at 30 m.
67 At which position does the block have maximum gravitational potential energy? Explain. Slide 79 / 113 68 At which position does the block have maximum elastic potential energy? Explain. Slide 80 / 113 69 At which position does the block have maximum kinetic energy? Explain. Slide 81 / 113
70 At which position does the block have maximum total energy? Explain. Slide 82 / 113 71 Suppose the block has a mass of 10 kg. Show your work for the following questions. Slide 83 / 113 a. What is the block's kinetic energy at position B if its velocity is 19.8 m/s? b. What is the block's gravitational potential energy at position B? c. Using your answers from (a) and (b), determine the block's total energy at position B. Slide 84 / 113 Questions 72 75 refer to the diagram below that shows a person jumping on a trampoline.
72 At which position does the person have maximum gravitational potential energy? Explain. Slide 85 / 113 73 At which position does the trampoline have maximum elastic potential energy? Explain. Slide 86 / 113 74 At which position does the person have maximum kinetic energy? Explain. Slide 87 / 113
75 At which position does the person have maximum total energy? Explain. Slide 88 / 113 Slide 89 / 113 Homework: Conservation of Energy Questions 76-80 refer to the diagram below which shows a ball dropped from rest at a height of h 0. Slide 90 / 113
76 At which position does the ball have maximum gravitational potential energy? Explain. Slide 91 / 113 77 At which position does the ball have maximum elastic potential energy? Explain. Slide 92 / 113 78 At which position does the ball have maximum kinetic energy? Explain. Slide 93 / 113
79 At which position does the ball have maximum total energy? Explain. Slide 94 / 113 80 The amount of total energy the ball possesses is 0.14 J. The mass of the ball is 0.005 kg. Use this information to answer the following: Slide 95 / 113 a. How much gravitational potential energy does the ball possess at h 1= 1.5 m? Show your work. b. How much kinetic energy does the ball possess at h 1= 1.5 m? Show your work. (Hint: Use the total energy and GPE of the ball.) Slide 96 / 113 Questions 81-86 refer to the diagram below, which shows a roller coaster cart that starts from rest at a height of 30m.
81 At which position does the car have maximum gravitational potential energy? Explain. Slide 97 / 113 82 At which position does the car have maximum elastic potential energy? Explain. Slide 98 / 113 83 At which position does the car have maximum kinetic energy? Explain. Slide 99 / 113
84 Where does the car have both GPE and KE, but more GPE? Explain. Slide 100 / 113 85 At which position does the car have maximum total energy? Explain. Slide 101 / 113 86 The car has a mass of 500 kg and moves with a speed of 9.9 m/s at position C. What is the total energy of the car? (Hint: the car possesses KE and GPE at position C. Also remember that TE is the sum of KE and PE.) Slide 102 / 113
Slide 103 / 113 Classwork #6: Types of Energy Resources 87 What is the difference between renewable resources and non-renewable resources? Slide 104 / 113 88 List two examples of a renewable energy resource. Slide 105 / 113
89 List two examples of a non-renewable energy resource. Slide 106 / 113 90 Explain how one of the energy resources we talked about in class demonstrates the law of conversation of energy. Slide 107 / 113 Slide 108 / 113 Homework: Types of Energy Resources
91 Explain the role of a turbine in "creating" electrical energy. Slide 109 / 113 92 How does a hydroelectric power plant transfer both potential and kinetic energy into electric energy? Slide 110 / 113 93 What type of energy resource does not use a turbine to convert mechanical energy into electrical energy? Slide 111 / 113
94 Why are fossil fuels considered to be nonrenewable energy resources? Slide 112 / 113 95 Why are fossil fuels not considered clean energy resources? Slide 113 / 113