Introduction to Physical Science



Energy Classwork Name: ____________________

Classwork #1

8th Grade PSI

1. Define energy.

2. What two things are necessary for work to be done on an object?

3. How can you determine the amount of work done on an object?

4. What would happen to an object’s velocity if positive work was done on an object?

5. Based on the diagram below, is positive or negative work being done on the object? Explain.

6. Based on the graph below, is positive or negative work being done on the object? Explain.

[pic]

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 of energy.

a. How much work was done on the ball as it fell? (HINT: Use your answer from #3)

b. What did the work?

8. What are the two major forms of energy?

9. What is the definition of mechanical energy?

10. What is the definition of non-mechanical energy?

Energy Homework Name: ____________________

Homework #1

8th Grade PSI

11. What would happen to an object’s velocity if no work was done on the object?

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.

13. At what time on the graph below does the object start to experience negative work being done on it? Explain.

[pic]

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?

15. What are the two forms of mechanical energy?

16. Name two examples of non-mechanical energy.

Kinetic Energy Classwork Name: ____________________

Classwork #2

8th Grade PSI

17. What two factors does kinetic energy depend upon?

18. If an object is accelerating, how does its kinetic energy change? Justify your answer.

19. If a moving mouse and an elephant have the same kinetic energy, can you determine which one is running faster? Explain.

20. If an object’s speed is doubled, how does its kinetic energy change?

21. If the mass of an object is doubled, how does its kinetic energy change?

22. How much kinetic energy does an 80 kg man have while running at 3 m/s? Show your work.

23. A 6 kg object has a speed of 20 m/s. What is its kinetic energy? Show your work.

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.

25. What is the SI unit for kinetic energy?

Kinetic Energy Homework Name: ____________________

Homework #2

8th Grade PSI

26. When is the only time that an object has no kinetic energy?

27. If an object is decelerating, how does its kinetic energy change?

28. How can a more massive object have the same kinetic energy as a less massive object?

29. If an object’s speed is cut in half, how does its kinetic energy change?

30. If the mass of an object is cut in half, how does its kinetic energy change?

31. How much kinetic energy does a 4 kg cat have while running at 9 m/s? Show your work.

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.

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?

Gravitational Potential Energy Classwork Name: ____________________

Classwork #3

8th Grade PSI

34. What three factors does gravitational potential energy depend upon?

35. If an object is thrown up in the air, how does its gravitational potential energy change? Explain.

36. If an object is falling, how does its gravitational potential energy change? Explain.

37. How does your gravitational potential energy change if you are placed on the moon where gravity is lower than on Earth?

38. If the mass of an object is cut in half, how does its gravitational potential energy change?

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.

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.

41. What is the gravitational potential energy of a 450 kg car at the top of a 25 m parking garage? Show your work.

42. A 2.0 kg toy falls from 2 m to 1 m. What is the change in GPE? Show your work.

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.

Gravitational Potential Energy Homework Name: ____________________

Homework #3

8th Grade PSI

44. When is the only time that an object has no gravitational potential energy?

45. How does your gravitational potential energy change if you are placed on Jupiter where gravity is larger than on Earth?

46. If the mass of an object is doubled, how does its gravitational potential energy change?

47. What is the SI unit for gravitational potential energy?

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.

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.

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.

51. An 80 kg person falls 60 m off of a waterfall. What is her change in GPE? Show your work.

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.

Elastic Potential Energy Classwork Name: ____________________

Classwork #4

8th Grade PSI

53. What two factors does elastic potential energy depend upon?

54. Define the term spring constant?

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.

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.

57. If a spring is stretched three times as far, by what factor does its elastic potential energy change? Does it increase or decrease?

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.

59. A spring with a spring constant of 250 N/m is stretched 0.5 meters. How much EPE does the spring have stored in it? Show your work.

60. A spring with a spring constant of 100 N/m is compressed 0.25 meters. How much elastic potential energy does it have stored in it? Show your work.

Elastic Potential Energy Homework Name: ____________________

Homework #4

8th Grade PSI

61. What is meant when a spring has a “relaxed” length?

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.

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?

64. A spring with a spring constant of 200 N/m is stretched 1 meter in length. How much EPE does the spring have stored in it? Show your work.

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.

66. A rubber band with a spring constant of 150 N/m is stretched 0.25 meters. How much EPE does it have stored in it? Show your work.

Conservation of Energy Classwork Name: ____________________

Classwork #5

8th Grade PSI

Questions 67 – 71 refer to the diagram below, which shows a block starting from rest at 30m.

[pic]

67. At which position does the block have maximum gravitational potential energy? Explain.

68. At which position does the block have maximum elastic potential energy? Explain.

69. At which position does the block have maximum kinetic energy? Explain.

70. At which position does the block have maximum total energy? Explain.

71. Suppose the block has a mass of 10kg. Show your work for the following questions.

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.

Questions 72 – 75 refer to the diagram below that shows a person jumping on a trampoline.

[pic]

72. At which position does the person have maximum gravitational potential energy? Explain.

73. At which position does the trampoline have maximum elastic potential energy? Explain.

74. At which position does the person have maximum kinetic energy? Explain.

75. At which position does the person have maximum total energy? Explain.

Conservation Energy Homework Name: ____________________

Homework #5

8th Grade PSI

Questions 76-80 refer to the diagram below which shows a ball dropped from rest at a height of h0.

[pic]

76. At which position does the ball have maximum gravitational potential energy? Explain.

77. At which position does the ball have maximum elastic potential energy? Explain.

78. Where does the ball have maximum kinetic energy? Explain.

79. At which position does the ball have maximum total energy? Explain.

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:

a. How much gravitational potential energy does the ball possess at h1= 1.5 m? Show your work.

b. How much kinetic energy does the ball possess at h1= 1.5 m? Show your work. (Hint: Use the total energy and GPE of the ball.)

Questions 81-86 refer to the diagram below, which shows a roller coaster cart that starts from rest at a height of 30 m.

[pic]

81. At which position does the car have maximum gravitational potential energy? Explain.

82. At which position does the car have maximum elastic potential energy? Explain.

83. At which position does the car have maximum kinetic energy? Explain.

84. Where does the car have both GPE and KE, but more GPE? Explain.

85. At which position does the car have maximum total energy? Explain.

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)

Energy Resources Classwork Name: ____________________

Classwork #6

8th Grade PSI

87. What is the difference between renewable resources and non-renewable resources?

88. List two examples of a renewable energy resource.

89. List two examples of a non-renewable energy resource.

90. Explain how one of the energy resources we talked about in class demonstrates the law of conservation of energy.

Energy Resources Homework Name: ____________________

Homework #6

8th Grade PSI

91. Explain the role of a turbine in “creating” electrical energy.

92. How does a hydroelectric power plant transfer both potential and kinetic energy into electric energy?

93. What type of energy resource does not use a turbine to convert mechanical energy into electrical energy?

94. Why are fossil fuels considered to be non-renewable energy resources?

95. Why are fossil fuels not considered clean energy resources?

Answers:

1. Energy is the ability to do work.

2. An applied force and the object must move a distance (i.e. have a displacement)

3. Efinal - Einitial.

4. It would increase.

5. Positive, the force applied is in the direction of the object’s motion

6. Positive, the object is accelerating

7. a.10 J

b. the air through air resistance

8. Mechanical and non-mechanical

9. The energy of an object due to its position or motion.

10. The energy of an object that is not due to its position or motion, but rather is energy at the atomic level.

11. It would remain constant.

12. Decreasing, air resistance is doing work against the man’s direction of motion (negative work)

13. After 1 second, because the velocity is decreasing

14. 0 J

15. Potential and kinetic energy

16. Electric and chemical energy

17. mass and velocity

18. it increases, velocity increases and kinetic energy is proportional to velocity squared.

19. Since the mouse has less mass than the elephant, it has to have a larger velocity in order to have the same kinetic energy.

20. 4 times larger

21. it is doubled

22. KE= ½ mv 2,

KE = ½ (80 kg) (3 m/s)2

KE=360 J

23. KE= ½ mv 2,

KE = ½ (6 kg) (20 m/s)2

KE= 1,200 J

24. KE= ½ mv 2= ½ (1000 kg) (5 m/s)2=

12,500J

KE= ½ mv 2= ½ (1000 kg) (10 m/s)2=

50,000J

change in KE= 50,000J- 12,500J =

37,500 J

OR

KE= ½ mv 2= ½ (1000 kg) ((10 m/s)2-(5 m/s)2)= 37,500J

25. Joule (J)

26. when the object is not moving (velocity equals 0)

27. it decreases

28. if the more massive object moves slower, the less massive object moves faster or both objects are at rest

29. it reduces by four times

30. it is cut in half

31. KE= ½ mv 2,

KE = ½ (4 kg) (9 m/s)2

KE=162 J

32. KE= ½ mv 2,

KE = ½ (2 kg) (5 m/s)2

KE=25 J

33. 7 times larger

34. mass, gravitational acceleration, and height

35. increases b/c object is increasing height above ground

36. decreases b/c object is decreasing height above ground

37. decreases

38. cut in half

39. GPE= mgh

= 1 kg (9.8 m/s2) (5 m)

= 49 J

40. GPE= mgh

= 200 kg (9.8 m/s2) (10 m)

= 19,600 J

41. GPE= mgh

= 450 kg (9.8 m/s2) (25 m)

= 110, 250 J

42. GPE= mgh

= 2 kg (9.8 m/s2) (1 m - 2 m)

= -19.6 J

43. GPE= mgh

= 3 kg (9.8 m/s2) (8 m - 5 m)

= 88.2 J

44. when the height is zero

45. increases

46. doubled

47. Joules (J)

48. GPE= mgh

= 75 kg (9.8 m/s2) (1000 m)

= 735,000 J

49. GPE= mgh

= 0.75 kg (9.8 m/s2) (3.1 m)

= 22.8 J

50. GPE= mgh

= 0.2 kg (9.8 m/s2) (11.33 m)

= 22.2 J

51. GPE= mgh

= 80 kg (9.8 m/s2) (0m- 60 m)

= - 47, 040 J

52. GPE= mgh

= 0.25kg (9.8 m/s2) (0.5 m - 2m)

= -3.7 J

53. The spring constant and the amount that the spring is stretched or compressed.

54. The “elasticity” of an object (how much an object stretches when an amount of force is applied).

55. Neither, both will have the same amount of potential energy because they are stretched and compressed the same distance.

56. The spring stretched 2X will have 4X more EPE since EPE is directly proportional to the distance of stretch squared.

57. 9X, increase

58. EPE = ½ kx2

= ½ (500 N/m) (1 m)2

= 250 J

59. EPE = ½ kx2

= ½ (250 N/m) (0.5 m)2

= 31.25 J

60. EPE = ½ kx2

= ½ (100 N/m) (0.25 m)2

= 3.1 J

61. The length of a spring when it is not stretched

62. B – spring constant is twice as large

63. 0 J

64. EPE = ½ kx2

= ½ (200 N/m) (1 m)2

= 100 J

65. EPE = ½ kx2

= ½ (500 N/m) (0.5 m)2

= 62.5 J

66. EPE = ½ kx2

= ½ (150 N/m) (0.25 m)2

= 4.7 J

67. A – it is at the highest height

68. None – there is no spring that is stretched or compressed

69. B – it will be going the fastest because it is at the lowest point.

70. All points have the same total energy due to the law of conservation of energy.

71. a. ½ mv2= ½ (10kg)(19.8 m/s)2= 1960J

b. mgh = (10 kg)(9.8 m/s2)(10 m) = 980 J

c. TE= KE + GPE= 1960 J + 980 J = 2940 J.

72. 3 – the person is at the highest point

73. 1 – the springs are stretched the most

74. 2 – the person is going the fastest when he leaves the trampoline

75. All points have the same total energy due to the law of conservation of energy.

76. ho – it has the highest height

77. None – the ball is not compressed or stretched at the three heights (NOTE: the ball does store elastic potential energy each time it hits the ground which is then converted to KE which is why it bounces up)

78. at the point of contact between h0 and h1 because it is falling from the highest height and that potential energy has transferred to kinetic energy.

79. All points have the same total energy

80. a. GPE= mgh= (0.005 kg)(1.5 m)(9.8 m/s2) = 0.0735J

b. TE= KE + GPE

0.147 J = KE + 0.0735J

therefore, KE = 0.0735 J

81. A – it is at the highest height

82. None – there is no spring that is stretched or compressed

83. B – it is at the lowest point and all GPE from A is converted into KE

84. C – There are only two places where the cart is elevated and moving, C and D. C has a higher elevation, so more GPE.

85. All points have the same total energy due energy conservation.

86. GPE = mgh = (500 kg)(9.8 m/s2)(25 m) = 122,500 J

KE= ½ mv2 = ½ (500 kg)(9.9 m/s)2= 24502.5 J

TE = KE + GPE = 24502.5 J + 122,500 J = 147,002 J

87. Renewable -energy resources that replenish themselves in a timely manner. Non-renewable- energy resources that exist in limited supply and cannot be replenished in a timey manner

88. Wind, solar, water, biomass, geothermal

89. Fossil fuels and nuclear energy.

90. Answers will vary but should discuss energy transformations of mechanical (or solar) energy to electrical energy.

91. As the turbine moves, the kinetic energy it has is transferred to a generator which converts that mechanical energy into electrical energy.

92. As the water falls from an elevated height, it converts gravitational potential energy into kinetic energy. As the water flows by the turbine it moves the turbine doing work and creating electricity.

93. Solar Energy

94. Because the amount of time it takes to produce fossil fuels is much larger compared to the amount of time it takes to consume fossil fuels,

95. Because carbon dioxide is produced when it is burned.

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