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Holtz Physics Exam 1
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Gravity
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The Greek mathematician Eratosthenes made measurements to show the size of _______.
Earth
When the Sun was directly overhead in Syene, why wasn't it directly overhead in Alexandria?
The Earth is a sphere
Earth, like everything else illuminated by the Sun, casts a shadow. Why does this shadow taper?
The sun is much larger than the Earth
How does the Moon's diameter compare with the distance between Earth and the Moon?
The Moon's diameter is 1/110 the distance between Earth and the Moon.
How does the Sun's diameter compare with the distance between Earth and the Sun?
The Sun's diameter is 1/110 the distance between Earth and the Sun
What are the circular spots of light seen on the ground beneath a tree on a sunny day?
These are pinhole images of the Sun
What is the role of equations in this book?
Equations are guides to thinking and show connections between concepts.
Equations in Conceptual Physics are used mainly _______.
guides to thinking
Distinguish between a hypothesis and a theory.
A hypothesis is an educated guess, whereas a theory encompasses well tested and verified hypotheses
In daily life, people are often praised for maintaining some particular point of view, for the "courage of their convictions." A change of mind is seen as a sign of weakness. How is this different in science?
When a scientist finds evidence that contradicts a law, then the law must be abandoned
What is the test for whether a hypothesis is scientific or not?
A hypothesis is scientific if it is possible to prove it wrong.
In daily life, we see many cases of people who are caught misrepresenting things and who soon thereafter are excused and accepted by their contemporaries. How is this different in science?
A scientist who lies in a scientific publication will suffer professional excommunication
Must people choose between science and religion?
No, there is no contradiction in being scientific and religious in one's thinking
Psychological comfort is a benefit of having solid answers to religious questions. What benefit accompanies a position of not knowing the answers?
Not knowing answers opens the mind to a lifetime of exploring.
A theory in science is ______.
a synthesis of well-tested ideas
A scientific hypothesis deemed valid must have a test for proving it ______.
wrong
Religion is concerned mainly with the ______.
Spiritual World
Why is physics considered to be the basic science?
Because all other sciences can be shown to be derived from it.
Science is a body of knowledge that
condenses knowledge into testable laws, is an ongoing human activity, describes order in nature.
To a fair approximation, Early Greeks knew the
Earth-Moon distance, size of Earth, size of the Moon
When the Sun shines on the Moon, the Moon casts a shadow
that sometimes falls on Earth, at all times, that is tapered.
Spots of sunlight on the ground cast through openings between leaves in trees above are actually
Images of the sun
A simple method of measuring the distance between the Earth and the Moon is to place in your line of sight to the Moon a
coin
An educated scientific guess is a
hypothesis
Facts in the field of science
are changeable
When a dishonest scientist reports false information, he or she
gets no second chance in the scientific community.
For a scientific hypothesis to be valid, there must be a test for proving it
wrong
Science, art, and religion normally need not contradict one another because
all three involve different domains.
A truly educated person is knowledgeable about
the arts, science, and religion
Technology is a tool that can
lead to a better world.
be socially beneficial.
be socially harmful when abused.
What two classes of motion did Aristotle advocate?
Natural motion and violent motion
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun.
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
Galileo found that a heavier stone does not fall significantly faster than a lighter one.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
What did Galileo demonstrate in his Leaning Tower of Pisa experiment?
He demonstrated that light and heavy objects gain the same amount of speed when falling.
Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.
a non-zero net force
What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?
10 N
Which of Newton's laws does the equilibrium rule illustrate?
Newton's first law
If while riding in a smooth-riding train, you toss a coin upward, the coin will normally land ______.
in your hand
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
The net force is 70 pounds to the right
Why do we say that force is a vector quantity?
A force has a magnitude and a direction.
According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
The diagonal is the resultant, or sum, of two vectors.
What is the resultant of a pair of one pound forces at right angles to each other?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors
What are the units for force?
Force can be expressed in newtons or pounds.
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force.
Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?
15 newtons up
The earliest and most influential Greek philosopher was Aristotle, who among many contributions taught that
violent motion requires a sustained push or pull, the four elements are earth, water, air, and fire, all motion is either natural or violent.
Science later greatly advanced when Galileo favored
experiment over philosophical discussions.
The first scientist to introduce the concept of inertia was
Galileo.
Inertia is defined as a
property of matter.
If no external forces act on a moving object, it will
continue moving at the same speed.
A hockey puck sliding across the ice finally comes to rest because
of friction
When no forces act on moving objects their paths are normally
straight lines
If gravity between the Sun and Earth suddenly vanished, Earth would continue moving in
a straight line path
A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is
about 30 m/s.
When a rocket ship gaining speed in outer space runs out of fuel, it
no longer gains speed.
A moving van with a stone lightly glued to the midpoint of its ceiling smoothly moves at constant velocity. When the glue gives way, the stone falls and hits the floor
exactly below the midpoint of the ceiling.
Two students engaged in a tug-of-war each pull a rope in opposite directions with a force of 400 N. The net force on the rope is
zero and rope tension is 400 N.
A force is a vector quantity because it has both
magnitude and direction.
A block pulled to the left with 15 N and to the right with 5 N at the same time experiences a net force of
10 N
When a pair of 10-N forces act on a box of candy, the net force on the box is
Any of the above depending on the directions of forces.
The resultant of a 40-N force at right angles to a 30-N force is
50 N
The net force on any object in equilibrium is
zero
The equilibrium rule, F = 0, applies to
objects or systems in uniform motion in a straight line, objects or systems at rest
The equilibrium rule applies to
vector quantities.
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is
10 N
The support force on a 10-N book at rest on a table is
10 N
The support force on a 30-kg dog sleeping on the floor is
about 300 N.
A gymnast performing somersaults in a high-flying plane moving at constant velocity needs to make
no adjustments.
A bird sitting on the limb of a tree is moving about 30 km/s with respect to the Sun. If the bird takes 1 second to drop down to a worm below, the worm would be 30 km downrange from the bird when it reached the ground. This faulty reasoning is best countered with Newton's
law of inertia.
As you read this in your chair, how fast are you moving relative to the chair? Relative to the Sun?
You are not moving relative to the chair, but you are moving over 100,000 km/h relative to the Sun.
A speedometer normally measures ______.
instantaneous speed
What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
30 km/h
The difference between speed and velocity involves ______.
direction
If a car moves with a constant velocity, does it also move with a constant speed?
Yes, because constant velocity requires constant speed in the same direction
If a car is moving at 90 km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
It maintains a constant speed, but does not maintain a constant velocity.
Which BEST describes what occurs when a body accelerates?
Change in velocity per unit time
A ball rolling down an inclined plane each second picks up ______.
the same amount of speed each second
Galileo discovered that when air resistance can be neglected, all objects fall with the same ______.
acceleration
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
10 km/h·s
What is the gain in speed per second for a freely falling object?
It gains approximately 10 m/s.
What exactly is meant by a "freely falling" object?
An object in free fall falls under gravity alone with no friction
In its first second of free fall, a dropped softball will fall a vertical distance of ______.
5m
What is the effect of air resistance on the acceleration of falling objects?
Air resistance decreases the acceleration of falling objects
What is the speed over the ground of an airplane flying at 100 km/h relative to the air caught in a 100-km/h right-angle crosswind?
141 km/h
Jogging Jake runs at 4 m/s along a train flatcar that moves at 10 m/s in the opposite direction. Jake's speed relative to the ground is
6 m/s
When you walk at an average speed of 4 m/s, in 5 s you'll cover a distance of
20 m.
A vehicle undergoes acceleration when it
gains/looses speed, changed diretions
If a car increases its velocity from zero to 60 m/s in 10 seconds, its acceleration is
6 m/s^2
An object covers a distance of 8 meters in the first second of travel, another 8 meters during the next second, and 8 meters again during the third second. Its acceleration is
0 m/s^2
A cart changes its speed from 90 m/s to 100 m/s in 10 seconds. During this interval its acceleration is
1 m/s^2
If an object moves with constant acceleration, its velocity must
change by the same amount each second.
A rock dropped from a 5-m height accelerates at 10 m/s2 and strikes the ground 1 s later. If the rock is dropped from a height of 2.5 m, its acceleration of fall is
the same
A ball tossed vertically upward rises, reaches its highest point, and then falls back to its starting point. During this time the acceleration of the ball is always
directed downward
A car's speed 3 seconds after accelerating from rest at 2 m/s2 is
6 m/s
A ball starting from rest at the top of an inclined plane gains a speed of 2 m/s for each second it rolls. What is its acceleration down the incline?
2 m/s^2
The time it takes a car to attain a speed of 30 m/s when accelerating from rest at 2 m/s2 is
15s
What is the acceleration of a car that starts from rest and 5 seconds later reaches a speed of 20 m/s?
4 m/s^2
If a stone falls to the bottom of a mineshaft in 6 seconds, then the depth of the shaft is about
180 m
If a freely falling object were equipped with a speedometer, its speed reading would increase each second by about
10 m/s
If a freely falling object were equipped with a speedometer on a planet where the acceleration due to gravity is 20 m/s2, then its speed reading would increase each second by
20 m/s
A ball is thrown upwards and returns to the same location. Compared with its initial speed its speed when it returns is about
the same
At one instant an object in free fall is moving downward at 50 m/s. One second later its speed is
60 m/s
At one instant a heavy object in air is moving upward at 50 m/s. One second later its speed is approximately
40 m/s
If you throw a ball straight downward (in the absence of air resistance), after leaving your hand its acceleration is
10 m/s^2
The total time it takes a projectile fired straight up at 10 m/s to reach the top of its path and return to its starting point is about
2s
When a ball thrown straight upwards reaches the very top of its path, its acceleration is
10 m/s ^2
Neglecting air resistance, a bullet fired straight down from the top of a high cliff has an acceleration of
10 m/s^2
Phil Physiker standing at the edge of a cliff throws one ball straight up and another ball straight down, both with the same speed. Neglecting air resistance, which ball hits the ground below with the greater speed?
neither, both hit the same time
A pot that falls from a ledge and hits the ground 45 m below hits the ground at
30 m/s
Phil leans over the edge of a cliff and throws a rock upward at 5 m/s. Neglecting air resistance, one second later the rock's speed is
5 m/s
Phil leans over the edge of a cliff and throws a rock upward at 5 m/s. Neglecting air resistance, two seconds later the rock's speed is
15 m/s
An 80-km/h airplane caught in a 60-km/h crosswind has a resultant speed of
100 km/h
A river 100 m wide flows 1 m/s due south. A boat that travels 1 m/s relative to the water is pointed due east as it crosses from the west bank. Relative to its starting point, the boat travels
141 m
A river 100 m wide flows due south at 1 m/s. A boat that travels 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat reaches the east bank
100 m farther south.
A motorboat that normally travels at 8 km/h in still water heads directly across a 6-km/h flowing river. The resulting speed of the boat is about
10 km/h
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