Download Motion and Speed Classwork Name

Motion and Speed Classwork
Classwork #1
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Motion and Speed Homework
Homework #1
Name: ____________________
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!)
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8th Grade PSI
Forces and Motion
Speed and Velocity Classwork
Classwork #2
Name: ____________________
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)
9.572
9.683
9.72
9.74
9.762
9.763
9.766
9.768
9.78
9.79
9.835
9.85
9.86
9.90
9.92
Name
Usain Bolt
Usain Bolt
Usain Bolt
Asafa Powell
Asafa Powell
Asafa Powell
Justin Gatlin
Asafa Powell
Tim Montgomery
Maurice Green
Donovan Bailey
Leroy Burrell
Carl Lewis
Leroy Burrell
Carl Lewis
Country
Jamaica
Jamaica
Jamaica
Jamaica
Jamaica
Jamaica
USA
Jamaica
USA
USA
Canada
USA
USA
USA
USA
Date
August 16, 2009
August 16, 2008
May 31, 2008
September 9, 2007
August 18, 2006
June 11, 2006
May 12, 2006
June 14, 2005
September 14, 2002
June 6, 1999
July 27, 1996
July 6, 1994
August 25, 1991
June 14, 1991
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?
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8th Grade PSI
Forces and Motion
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.
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8th Grade PSI
Forces and Motion
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.
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8th Grade PSI
Forces and Motion
Speed and Velocity Homework
Homework #2
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
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.
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8th Grade PSI
Forces and Motion
Graphing Motion Homework
Homework #3
Name: ____________________
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.
Name
Susie (6th)
Joe (7th)
Thomas (8th)
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10m
4s
5s
6s
20m
9s
15s
8s
30m
11s
19s
11s
40m
15s
24s
15s
8th Grade PSI
50m
21s
29s
20s
60m
23s
33s
24s
70m
28s
36s
28s
80m
32s
41s
31s
90m
37s
46s
35s
Forces and Motion
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.
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8th Grade PSI
Forces and Motion
Acceleration Classwork
Classwork #3
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
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?
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8th Grade PSI
Forces and Motion
Acceleration Homework
Homework #4
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
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?
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8th Grade PSI
Forces and Motion
Forces and Friction Classwork
Classwork #4
Name: ____________________
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?
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8th Grade PSI
Forces and Motion
Forces and Friction Homework
Homework #5
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Gravity and Equilibrium Classwork
Classwork #5
Name: ____________________
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?
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8th Grade PSI
Forces and Motion
Gravity and Equilibrium Homework
Homework #6
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Newton’s First Law Classwork
Classwork #6
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Newton’s First Law Homework
Homework #7
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Newton’s Second Law Classwork
Classwork #7
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Newton’s Second Law Homework
Homework #8
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
Newton’s Third Law Homework
Homework #9
Name: ____________________
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.
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8th Grade PSI
Forces and Motion
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.
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8th Grade PSI
Forces and Motion
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
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8th Grade PSI
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
Forces and Motion
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
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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
8th Grade PSI
Forces and Motion
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.
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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.
8th Grade PSI
Forces and Motion
100
90
80
70
60
Susie
50
Joe
40
Thomas
30
20
10
0
0
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10
20
30
40
8th Grade PSI
50
Forces and Motion