motion and speed classwork name: classwork...

www.njctl.org 8th Grade PSI Forces and Motion

Motion and Speed Classwork Name: ____________________ Classwork #1 8th Grade PSI

1. Define motion.

2. When you look at the ground, you seem to be at rest. Why is this? Why does someone in space see you moving in a circle?

3. Define speed.

4. What is the formula for measuring the speed of an object?

5. Lance Armstrong can ride his bicycle at speeds of 15 m/s. If he is traveling at this speed, how long will it take him to travel 81.9 meters? Show your work.

6. John is growing another crop of corn this year. He plows a row of his field in 90 seconds. If each row is 384 meters long, how fast does John drive his tractor? Show your work.

7. Julia is learning how to ride her tricycle. It takes her 10 seconds to go from one end of the driveway to the other. If she travels at 3 m/s, how far does she travel? Show your work.


Motion and Speed Homework Name: ____________________ Homework #1 8th Grade PSI

8. How can you tell that an object is in motion?

9. What is a frame of reference?

10. How long does it take a snail to travel a distance of 3 ft at 0.1 ft/sec? Show your work.

11. How far does a cat run if it travels at a speed of 3 m/s for 25 seconds? Show your

work.

12. A racecar driver frequently drives her racecar at 67 m/s for as long as she can. If she drives her car at that speed for 22 seconds, how far will she travel? Show your work.

13. Everyone in Paperville needs their newspaper before 6 a.m. on Monday. If it takes the delivery boy 3 hours to deliver the papers at 12 m/s, what is the distance of the paper route in Paperville? Show your work. (HINT: convert 3 hours to seconds before using the speed equation!)


Speed and Velocity Classwork Name: ____________________ Classwork #2 8th Grade PSI

The 100m dash is a sprint race in track and field competitions where athletes are timed on how long it takes them to sprint a distance of 100m. It has been an Olympic sport since 1896. The table below shows some of the record setting times achieved by athletes running the 100m dash. Use the data table to answer the questions.

Time (s) Name Country Date

9.572 Usain Bolt Jamaica August 16, 2009

9.683 Usain Bolt Jamaica August 16, 2008

9.72 Usain Bolt Jamaica May 31, 2008

9.74 Asafa Powell Jamaica September 9, 2007

9.762 Asafa Powell Jamaica August 18, 2006

9.763 Asafa Powell Jamaica June 11, 2006

9.766 Justin Gatlin USA May 12, 2006

9.768 Asafa Powell Jamaica June 14, 2005

9.78 Tim Montgomery USA September 14, 2002

9.79 Maurice Green USA June 6, 1999

9.835 Donovan Bailey Canada July 27, 1996

9.85 Leroy Burrell USA July 6, 1994

9.86 Carl Lewis USA August 25, 1991

9.90 Leroy Burrell USA June 14, 1991

9.92 Carl Lewis USA September 24, 1988

14. According to the table, who holds the current world record for finishing the 100 m

sprint the fastest?

15. By how much time did Tim Montgomery beat the previous world record holder?

16. The first recorded world record is 10.8 seconds set by Luther Cary (USA 1891).

How much time has been taken off the world record since it was first set in 1891?


17. At what average speed did Asafa Powell run the 100 m in 2007? Show your work.

18. Usain Bolt broke the world record on May 31, 2008. He then broke his own world

record about two months later. What was his average speed on each day? Show

your work for both days.

19. Can you use the table to calculate instantaneous speeds? How about velocities?

Explain why or why not.

20. How much faster (in terms of average speed) did Leroy Burrell run on June 14,

1991 to break the record set by Carl Lewis on September 24, 1988? Show your

work.

21. If an athlete were to run the 100 m dash at a speed of 10.5 m/s, would they beat

Usain Bolt’s current world record? Justify your answer.

22. What was Justin Gatlin’s average speed on the day that he broke the world

record? Show your work.


23. Calculate the speed achieved by Maurice Green in 1999. At this average speed,

how long would it take Maurice to run 315 meters? Show your work.


Speed and Velocity Homework Name: ____________________ Homework #2 8th Grade PSI

24. What is the difference between average speed and instantaneous speed?

25. Can average speed ever be equal to instantaneous speed? Explain.

26. What is the average speed of a dog that runs 100 m in 30 s? Show your work.

27. Describe two examples of average speed and two examples of instantaneous speed.

28. The Admiral train is traveling east at 100 mph and the Alamo train is traveling west at 100 mph. Do they have the same speed? Do they have the same velocity? Explain why or why not.


29. Train A leaves New York for California at the same time Train B leaves California for New York. They are 2900 miles apart. They both travel at an average speed of 120 mph.

a. What is the velocity of train A?

b. What is the velocity of train B?

c. How long will it take before they meet? Show your work.


Graphing Motion Homework Name: ____________________ Homework #3 8th Grade PSI

30. It is Field Day at your school and everyone is ready for the potato sack race. Each grade has selected one person to enter the race. There are nine checkpoints along the racecourse. The table below shows how long it took each student to get to each checkpoint. Graph the motion of the three contestants using a separate color/line pattern for each contestant. Be sure to plot position on the y-axis and time on the x-axis and label each axis.

PrintFreeGraphPaper.com

Name 10m 20m 30m 40m 50m 60m 70m 80m 90m

Susie (6th) 4s 9s 11s 15s 21s 23s 28s 32s 37s

Joe (7th) 5s 15s 19s 24s 29s 33s 36s 41s 46s

Thomas (8th) 6s 8s 11s 15s 20s 24s 28s 31s 35s


31. Who won the race? Explain how you can tell from the graph.

32. Who had the fastest speed from 0- 30m? Justify your answer with speed calculations for each student.

33. Who had the fastest speed from 0-60m? Justify your answer with speed calculations for each student.


Acceleration Classwork Name: ____________________ Classwork #3

34. Define acceleration.

35. Write the formula for measuring the acceleration of an object. Be sure to explain

what each part of the equation is.

36. What is the SI unit of measurement for acceleration?

37. Explain 3 different ways that an object can accelerate.

38. What is the acceleration of a car that starts at rest and increases its speed to 10

m/s in 2 seconds? Show your work.

39. What is the acceleration of an object that starts at 10 m/s and slows to 2 m/s in 4

seconds? Show your work.


40. Describe the speed and velocity of an object whose motion is shown in the speed

vs time graph below.

41. Describe the speed and velocity of an object whose motion is shown in the

position vs time graph below. What happens to the distance covered during each

5 second time interval?


Acceleration Homework Name: ____________________ Homework #4

42. A student runs at constant speed on a circular racetrack. Does the student

accelerate? Justify your answer.

43. A car increases its speed. Is this acceleration positive or negative? Explain.

44. What is the acceleration of a rocket that is travelling at 20 m/s and increases it’s

velocity to 40 m/s in 4 seconds? Show your work.

45. What is the acceleration of a dragster that deploys a parachute when travelling at

33 m/s and slows to rest in 11 seconds? Show your work.

46. Describe the speed of an object whose motion is shown in the speed vs time

graph below.


47. Describe the speed of an object whose motion is shown in the position vs time

graph below. What happens to the distance covered during each 5 second time

interval?


Forces and Friction Classwork Name: ____________________ Classwork #4

48. Define a force.

49. What do forces do to objects? Describe an example.

50. What is the “BIG IDEA” about the relationship between forces and acceleration?

51. What is the unit for measuring force in the SI system of measurement?

52. Determine the net force in the diagram seen below. Show how you came up with

your answer.

53. Define friction and explain its effect on motion.

54. What is static friction?


Forces and Friction Homework Name: ____________________ Homework #5

55. A force is a push or pull acting on an object. How do forces affect motion when the

forces are

a. balanced?

b. unbalanced?

56. What happens to the motion of any object that feels an unbalanced force?

57. What types of friction occur when you ride a bike through a puddle? Justify your

answer.


Gravity and Equilibrium Classwork Name: ____________________ Classwork #5

58. In your own words, define the law of gravitation.

59. What is the formula for measuring the weight of any object? Identify each part of

the formula.

60. Explain why the weight of a barbell is smaller on the moon than on Earth.

61. What happens to the force of gravity as any 2 objects move farther apart?

62. When is an object said to be in free fall? Give an example.

63. Define equilibrium and relate it to forces.

64. Calculate the net force acting on the block in the diagram seen below. Show your

work. What is the direction of the net force?


Gravity and Equilibrium Homework Name: ____________________ Homework #6

65. As we move away from the center of the Earth, what happens to the force of

gravity?

66. Explain why Jupiter’s gravitational constant is stronger than Mercury’s gravitational

constant.

67. What is the weight of a 99 kg man on Earth? Show your work.

68. What happens to the motion of any object that feels an unbalanced force?

69. If an object is in equilibrium, then the forces must be _____________________?

70. Calculate the net force acting on the block seen in the diagram below. Show your

work.

71. Is the object in #70 in equilibrium? Explain.


Newton’s First Law Classwork Name: ____________________ Classwork #6

72. Who were the early scientists that first studied/explained motion?

73. What were some of the advances that Sir Isaac Newton made in the area of

physics?

74. Define Newton’s 1st law of motion and give an everyday example of Newton’s 1st

law of motion at work.

75. What is the relationship between an object’s mass and the amount of inertia it

exhibits? Give an example to answer this question.


Newton’s First Law Homework Name: ____________________ Homework #7

76. Define inertia.

77. Which object has more inertia? A running boy or an automobile at rest? Why?

78. In your own words, explain an example of Newton’s 1st law of motion for moving

and non-moving objects.


Newton’s Second Law Classwork Name: ____________________ Classwork #7

79. How does applying a force to an object affect its motion?

80. What is the acceleration of a 100 kg canoe that feels a force of 1000N? Show your

work.

81. Suppose the canoe in problem #80 is loaded to have a total mass of 500 kg, but

the force stays the same at 1000 N. Will the canoe slow down or speed up? Why?

Justify your answer by calculating the new acceleration. Show your work.

82. A tennis ball with a mass of 0.314 kg, is accelerated at a rate of 164 m/s2 when hit by a professional tennis player. What force does the player’s tennis racket exert on the ball? Show your work.

83. You push a friend sitting on a swing. She has a mass of 50 kg and accelerates at a rate of 4 m/s2. Find the force you exerted. Show your work.

84. You want to push another friend to accelerate them at the same rate of 4 m/s2.

This friend has a mass of 70 kg. Will you push as hard as you did in #83? Why or

why not? Justify your answer by calculating the new force. Show your work.


Newton’s Second Law Homework Name: ____________________ Homework #8

85. You pull on a box with 50N of force. Your friend pulls on an identical box with 100N

of force. Compare the motion of both boxes. Explain your answer.

86. A person uses 50N of force to push a cart. If the mass of the cart increases, but

the person uses the same amount of force, what is the effect on the resulting

acceleration?

87. What is the acceleration of a 1000 kg car that feels a force of 5000 N? Show your

work.

88. What force causes a 1 m/s2 acceleration of a 5 kg bowling ball? Show your work.

89. What is the mass of an object that accelerates at a rate of 3 m/s2 when acted upon

by a 30 N force? Show your work.

90. A worker drops his hammer off the roof of a house. The hammer has a mass of 9

kg, and gravity accelerates it at the usual 9.8 m/s2. What is the gravitational force

acting on the hammer? What is the weight of the hammer? Show your work.


Newton’s Third Law Homework Name: ____________________ Homework #9

91. Explain how a rocket works using Newton’s third law of motion.

92. Compare and contrast momentum and inertia.

93. Compare the momentum of a fly and a train travelling at the same velocity.

94. How does sitting in your chair relate to Newton’s 3rd law of motion?

95. A dog digs a hole in the ground by pushing dirt back with his paws. Describe an

action reaction pair in this scenario.


96. What is the momentum of a 13 kg shot put travelling at 3 m/s? Show your work.

97. What is the momentum of the same shot put travelling at 1.5 m/s? Show your

work.

98. If the velocity of an object is cut in half, what happens to the momentum of the

object? How about if it is doubled?

99. Define “conservation of momentum” and give an example of this principle in the

real world.


Answers 1. A change in position relative to a

reference frame.

2. You are seeing the ground at rest

because you are moving at the

same speed as the ground.

Someone in space sees you

moving in a circle because they

are in a different reference frame

relative to you.

3. Speed is change in total distance

traveled divided by time.

4. S = d/t

5. 81.9 m/ 15 m/s = 5.46 s

6. 384 m/ 90 s = 4.27 m/s

7. 3 m/s x 10 s = 30 m

8. Change in position

9. A background by which motion is

measured.

10. 3 ft/ 0.1 ft/s = 30 s

11. 3 m/s x 25 s = 75 m

12. 67 m/s x 22 s = 1,474 m

13. 3 hrs x 3600 = 10,800 s

12 m/s x 10,800 s = 129,600 m

14. Usain Bolt 15. 0.01 seconds 16. 1.228 seconds 17. 100 m/9.74 s = 10.27 m/s 18. 100 m/9.72 s = 10.28 m/s

100 m/9.68 s = 10.33 m/s 19. No. The data only shows the

total time and distance traveled. This is not enough information to determine the speed at any given instant during the race. No to velocities as well because you don’t know the direction of each runner.

20. Leroy: 100 m/9.90 s = 10.10 m/s Carl Lewis:100 m/9.92 s = 10.08 m/s 10.10 m/s–10.08 m/s= 0.02 m/s

21. Yes. 100 m/10.5 m/s = 9.52 seconds (this is less than Usain Bolt’s record time of 9.572 seconds)

22. 100 m/9.766 s = 10.24 m/s 23. 100 m/9.79 s = 10.21 m/s

315 m/10.21 m/s = 30.85 seconds

24. Average speed is computed

mathematically with the total

distance divided by the total time

of an entire trip. Instantaneous

speed is the speed at any one

moment during the trip.

25. Yes. If travelling at a constant

speed inst speed = avg speed.

26. 100 m/ 30 s = 3.33 m/s

27. Answers will vary

28. Yes, same speed of 100mph

because they cover the same

amount of distance per unit of

time. No, different velocity

because they are traveling in

different directions.

29. a. 120mph west

b. 120mph east

c. They will meet at half the

distance, 1450 m.

1450 m/ 120 mph =12.08 hours

30. See graph below at end of

Answer Key

31. Thomas, his time is the smallest

at the end of the race (90 m)

32. Suzie and Thomas were tied.

Suzie: 30 m/ 11 s = 2.7 m/s

Joe: 30 m/ 19 s = 1.5 m/s

Thomas: 30 m/ 11 s = 2.7 m/s

33. Suzie.

Suzie: 60 m/ 23 s = 2.6 m/s

Joe: 60 m/ 33 s = 1.8 m/s


Thomas: 60 m/ 24 s = 2.5 m/s

34. Rate change of velocity over a

period of time.

35. A = Vf -Vo / t

A=acceleration

Vf = final velocity

Vo= initial velocity

t= time over which velocity

changes

36. m/s2 OR m/s /s

37. Increase speed, decrease speed,

change direction.

38. (10 m/s – 0 m/s) / 2 s = 5 m/s2

39. (2 m/s – 10 m/s) / 4 s = – 2 m/s2

40. Increase in speed/velocity at a

constant rate.

41. Positive acceleration –

speed/velocity increases at a

constant rate. The object covers

more and more distance during

each 5 s interval.

42. Yes. They change direction as

they run.

43. + a = increase in velocity/speed.

44. (40 m/s – 20 m/s) / 4 s = 5 m/s2

45. (0 m/s – 33 m/s) / 11 s = – 3.33

m/s2

46. Negative acceleration, speed

slows at a constant rate.

47. Negative acceleration- speed

slows at a constant rate. The

object covers less and less

distance during each 5 s interval.

48. Push or pull

49. Cause an object to change its

motion. Examples will vary (i.e. a

bat causes a ball to change its

direction).

50. Unbalanced forces cause

acceleration

51. Newton (N) – kgm/s2

52. 20 N + (-8 N) = 12 N

53. Friction is a force that opposes

motion and typically slows a

moving object.

54. Static friction is friction acting on

objects that are not moving.

55. a. Balanced = Equilibrium = no

acceleration.

b. Unbalanced = acceleration

56. It experiences acceleration.

57. Fluid (moving through wet

puddles), rolling (bike wheels roll

on ground), and kinetic/sliding

(bike is moving)

58. All objects that have mass exert

gravitational forces. Answers will

vary.

59. Weight = mass (gravitational

acceleration)

60. The barbell weighs less on the

moon because acceleration due

to gravity, “g”, is less on the

moon.

61. Force of gravity is reduced.

62. When the only force acting on the

object is gravity. Examples will

vary.

63. Equilibrium is when all forces are

balanced and cancel out to equal

zero.

64. 22 N + (-10 N) + (-5 N) = 7 N, to

the right.

65. The force of gravity decreases

66. The force of gravity on Jupiter is

greater because Jupiter has more

mass than Mercury.

67. 99 kg (9.8 m/s2) = 970 N

68. It accelerates.

69. Balanced


70. 100 N + (-50 N) + (-50 N) = 0 N

71. Yes, because the net force is 0 N

meaning all forces are balanced.

72. Galileo & Aristotle

73. Devised laws of motion, and law

of gravitation

74. A body in motion stays in motion,

a body at rest stays at rest,

unless acted upon by an

unbalanced force. Ex. A baseball

slides to a stop due to friction

(unbalanced force).

75. More mass = more inertia. Ex)

hard to stop a moving bus.

76. A resistance in change in motion

due to mass.

77. An automobile because it has

more mass.

78. Answers will vary.

79. A force will cause acceleration if

it is unbalanced.

80. 1000 N / 100 kg = 10 m/s2

81. slow down b/c more mass. 1000

N/ 500 kg = 2 m/s2

82. 0.314 kg (164 m/s2) = 51.5 N

83. 50 kg (4 m/s2) = 200 N

84. push harder because more mass,

70 kg (4 m/s2) = 280N

85. Your friend’s box accelerates

more because your friend uses

twice as much force.

86. The acceleration decreases.

87. 5000 N / 1000 kg = 5 m/s2

88. 5 kg (1 m/s2) = 5 N

89. 30 N / 3 m/s2 =10 kg

90. 9 kg (9.8 m/s2) = 88.2 N, weight

will be the same.

91. Action of gases in one direction,

cause the rocket to move in the

opposite direction.

92. Both involve mass in some way.

Momentum is zero at rest. Inertia

is still present at rest.

93. Fly has less momentum because

it has less mass.

94. You push down on the chair and

the chair pushes back with equal

and opposite force.

95. Action: The dog exerts a force

that pushes back on the dirt.

Reaction: The dirt exerts a force

that pushes forward on the dog’s

paws.

96. 13 kg (3 m/s) = 39 kgm/s

97. 13kg (1.5 m/s) = 19.5 kgm/s

98. halving velocity = halved

momentum; doubling velocity =

doubled momentum

99. During a collision, the momentum

of the system stays the same.

Ex) Perfect bouncy ball off wall.


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