Homework 1 & 2

A ball is thrown vertically upward with an initial speed of 30 m/s. How long does it take to come back down? 3 seconds 6 seconds 9 seconds 12 seconds

6 seconds

A projectile is launched at 30° above ground level. What other angle at the same speed will result in the same range? 60° 15° any angle at 60° or greater 45°

60

A ball is dropped from rest off a cliff, and it hits the ground in 4 seconds. How far did it drop? 20 m 40 m 80 m 160 m

80m

Why do we say that force is a vector quantity? A force is a scalar quantity. A force has a magnitude, but not a direction. A force is measured in pounds, and pounds are a vector quantity. A force has a magnitude and a direction.

A force has a magnitude and a direction.

Consider Nellie hanging at rest in Figure 2.11. If the ropes were vertical, with no angle involved, what would be the tension in each rope? The tension in each rope would be half of the gravity force. The tension in each rope would be twice the gravity force. The tension would be zero in both ropes. The tension in each rope would be equal to the gravity force.

The tension in each rope would be half of the gravity force.

When you push against a wall, what pushes back? Your fingers push back. Nothing pushes back. Your hand pushes back. The wall pushes back.

The wall pushes back

As a skydiver gains speed in falling through the air, air resistance _______. cancels weight. becomes negligible when terminal speed is reached. decreases. increases.

increases.

The force that propels a rocket is that provided by _______. energetic reactions as the fuel is burned. ejected fuel. decreased mass the expelled gas pushing on the rocket

the expelled gas pushing on the rocket

A 1-kg stone and a 10-kg stone have the same acceleration in free fall because _______. the ratio of weight to mass is the same for each. the force of gravity is the same on each. they both fall equally. air resistance has no effect

the ratio of weight to mass is the same for each.

A boxer cannot exert much force on a piece of tissue paper suspended in air because _______. there is little follow-through with the punch. the time of the interaction is too brief the tissue paper has too little mass to exert as much force on the boxer's fist. the tissue lacks enough strength.

the tissue paper has too little mass to exert as much force on the boxer's fist.

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 m/s2 10 km/h·s 100 km/h·s 1 km/h·s

10 km/h·s

How much support force acts on a 200-N girl standing on a weighing scale? Less than 200 N No support force unless she stands on the floor More than 200 N 200 N

200N

Distinguish between a hypothesis and a theory. A hypothesis and a theory have both been tested and verified by experiment. A hypothesis is an educated guess, whereas a theory encompasses well tested and verified hypotheses. A theory is an educated guess, whereas a hypothesis has been tested and verified by experiment. A hypothesis and a theory are both educated guesses.

A hypothesis is an educated guess, whereas a theory encompasses well tested and verified hypotheses.

How does acceleration depend on the net force? Acceleration is inversely proportional to the net force. Acceleration is proportional to the net force. Acceleration is independent of the net force. Acceleration is equal to the net force.

Acceleration is proportional to the net force.

What exactly is a projectile? An object that follows a parabolic trajectory An object that continues in motion by its own inertia An object with independent horizontal and vertical components of motion An object with no air resistance

An object that continues in motion by its own inertia

Why is physics considered to be the basic science? Physics is about how atoms combine to form molecules. As physicist Paul Tipler says about sciences other than physics, "What other sciences?" Because all other sciences can be shown to be derived from it. Physics involves matter that is alive.

Because all other sciences can be shown to be derived from it.

Which BEST describes what occurs when a body accelerates? Change in direction Change in velocity per unit time Change in velocity. Change

Change in velocity per unit time

What two units of measurement are necessary for describing speed? Average speed and distance Distance and length Average speed and time Distance and time

Distance and time

What are the units for force? Force must be measured in newtons; it can never be measured in pounds. Force must first be measured in newtons, then converted to pounds. Force can be expressed in newtons or pounds. Force must be measured in pounds and then converted to newtons.

Force can be expressed in newtons or pounds.

In the apple-pulling-the orange sequence in this chapter, what is the force that accelerates the system across the floor? The resistance to motion by the orange Internal forces. Friction between the apple and the floor. The backward pull by the orange

Friction between the apple and the floor.

What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa? Galileo found that a heavier stone falls significantly faster than a lighter one. Galileo found that stones fall faster proportional to their weight. Galileo found that a heavier stone does not fall significantly faster than a lighter one. Galileo found that air resistance significantly slowed falling stones.

Galileo found that a heavier stone does not fall significantly faster than a lighter one.

What kind of speed is registered by an automobile speedometer? Maximum speed Average speed Minimum speed Instantaneous speed

Instantaneous speed

When an object is thrown upward, how much speed does it lose each second (ignoring air resistance)? It loses 1 m/s of speed each second. It loses 10 m/s each second. It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.

It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.

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 velocity, but not a constant speed. It maintains a constant speed and a constant velocity. It does not maintain a constant speed or a constant velocity. It maintains a constant speed, but does not maintain a constant velocity.

It maintains a constant speed, but does not maintain a constant velocity.

In the string-pull illustration in Figure 4.8, a sharp jerk on the bottom string results in the bottom string breaking. Does this occur because of the ball's weight or its mass? Weight Mass Neither mass nor weight Both mass and weight

Mass

The action is: Earth pulls on Moon. What is the reaction? Moon pushes on Earth. Earth pushes on Moon. Moon pulls on Sun. Moon pulls on Earth.

Moon pulls on Earth.

The unit of mass is the kilogram, and the unit of weight is the _______. Newton. m/s2 kilogram also. metric mass

Newton

Can you physically touch a person without that person touching you with the same amount of force? No, when you touch a person, they must touch you with an equal and opposite force. Yes, when a heavier person touches a lighter person, the lighter person touches back with less force. Yes, you can touch a person while they choose to not touch you back. Yes, when you touch a person, they touch you back with a force that is slightly less due to friction.

No, when you touch a person, they must touch you with an equal and opposite force.

If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations? The cannon pushes on the cannon ball with a much greater force than the cannon ball pushes on the cannon. Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force. The cannon weighs so much that friction with the ground alone prevents it from accelerating. The force from the cannon ball on the cannon produces little acceleration because it lasts for such a brief time.

Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.

A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls? It increases while rising and while falling. It decreases while rising, but it increases while falling. It increases while rising, but it decreases while falling. Rising or falling, it does not change.

Rising or falling, it does not change.

What is the acceleration of a falling object that has reached its terminal velocity? The acceleration is g2. The acceleration is g. The acceleration is 0. The acceleration is -g.

The acceleration is 0.

How does the direction of acceleration compare with the direction of the net force that produces it? The acceleration is opposite the direction of the net force. The acceleration is in the direction of the net force. The acceleration is at right angles to the net force. The acceleration is zero.

The acceleration is in the direction of the net force.

If the mass of a sliding block is tripled while a constant net force is applied, by how much does the acceleration change? The acceleration is reduced to 1/3 of its original value. The acceleration remains the same. The acceleration triples. The acceleration is zero.

The acceleration is reduced to 1/3 of its original value.

What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball's acceleration? The ball gained more speed every second, so it had an increasing acceleration. The ball gained more speed every second, so it had a constant acceleration. The ball had constant acceleration, so it gained the same speed every second. The ball gained less speed every second, so it had a decreasing acceleration.

The ball gained more speed every second, so it had a constant acceleration.

How does a helicopter get its lifting force? The helicopter exerts a downward force on Earth; the reaction force of Earth on the helicopter is called lift. The helicopter exerts downward forces on air; the reaction forces of the air on the helicopter are upward and called lift. The helicopter exerts upward forces on the air; the reaction forces of the air on the helicopter are downward and called lift. The helicopter exerts downward forces on the air that are slightly greater than the force of gravity, so it can hover.

The helicopter exerts downward forces on air; the reaction forces of the air on the helicopter are upward and called lift.

If a block is moving to the left at a constant velocity, what can one conclude? There is exactly one force applied to the block. The net force applied to the block is directed to the left. The net force applied to the block is zero. There must be no forces at all applied to the block.

The net force applied to the block is zero.

A ball rolling down an inclined plane each second picks up ______. decreasing amounts of speed each second. acceleration, not speed. the same amount of speed each second increasing amounts of speed each second.

The same amount of speed each second

Which of the following is NOT a statement or consequence of Newton's third law? All forces come in pairs. No force can exist on its own. Every force has an opposite and equal reaction. There can never be only one force acting on an object.

There can never be only one force acting on an object.

What is the main difference between speed and velocity? Velocity is constant, but speed always changes. Speed is constant, but velocity always changes. Speed includes a direction, but velocity does not. Velocity includes a direction, but speed does not.

Velocity includes a direction, but speed does not.

In the string-pull illustration in Figure 4.8, a gradual pull of the lower string results in the top string breaking. Does this occur because of the ball's weight or its mass? Both weight and mass Mass Neither weight nor mass Weight

Weight

Which depends on gravity? Force. Mass Weight. Acceleration.

Weight

Acceleration is generally defined as the time rate of change of velocity. When can it be defined as the time rate of change of speed? When moving in a straight line, the time rate of change of speed is acceleration. When moving in a straight line, the time rate of change of speed is called velocity. When moving in a circle, the time rate of change of speed is called average speed. When moving in a circle, the time rate of change of speed is always zero.

When moving in a straight line, the time rate of change of speed is acceleration.

Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force? Yes, you pull up on Earth with the same force. No, the contact force from the ground cancels the force of Earth on you. No, the contact force from the ground cancels the force by you on Earth. Earth exerts a much greater force on you than you exert on Earth.

Yes, you pull up on Earth with the same force.

A theory in science is a synthesis of well-tested ideas an agreement between trained investigators an educated guess forever true

a synthesis of well-tested ideas

A fact in science is ______. an agreement between trained investigators forever true an educated guess a synthesis of well-tested ideas

an agreement between trained investigators

Two forces, of magnitude 4N and 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________. Check all that apply. cannot have a magnitude equal to 5N cannot have a magnitude equal to 10N cannot have the same direction as the force with magnitude 10N must have a magnitude greater than 10N

cannot have a magnitude equal to 5N

How far will it fall during this time?

d = -240 m

When you drop a rubber ball on the floor it bounces back. The force exerted on the ball to produce bouncing is by the floor. ball. need more information

floor

As a ball bounces from a floor, its acceleration off the floor between bounces is g. significantly less than g. slightly more than g. significantly more than g.

g.

The acceleration of free fall is about 10 m/s2. Why does the seconds unit appear twice? The second appears once in the denominator of the unit for speed and once for the interval of time. Seconds cancel seconds in the denominator. Seconds appear once for velocity and again for speed. The seconds appear as the area of a graph, so they should be squared.

he second appears once in the denominator of the unit for speed and once for the interval of time.

The horizontal and vertical components of velocity for a projectile are __________. independent of each other equal for angles greater than 45° parts of a parabola dependent on each other

independent of each other

Air resistance on a parachutist at terminal speed _______. is the same for both a heavy and light person with the same size parachutes. is less for a heavy person is greater for a heavier person no longer depends on speed

is greater for a heavier person

A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________. continuously changing direction moving at constant velocity moving with a constant nonzero acceleration moving with continuously increasing acceleration

moving with a constant nonzero acceleration

What is its average velocity during this 7.0-s interval?

v = -34 ms

What is the instantaneous velocity of a freely falling object 7.0 s after it is released from a position of rest?

v = -69 ms

A scientific hypothesis deemed valid must have a test for proving it ______. none of these correct more than one time wrong

wrong

A projectile is launched vertically at 100 m/s. If air resistance can be ignored, at what speed will it return to its initial level? 200 m/s 10 m/s 0 m/s 100 m/s

100m/s

While you are in a bus that moves at 100 km/h you walk from the back to the front at 10 km/h. What is your speed relative to the road outside? 10 km/h 90 km/h 110 km/h. 100 km/h

110 km/h

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 0 newtons 15 newtons down 30 newtons up

15 newtons up

A bird is flying at a constant height 5 meters above the ground and drops an egg with an initial horizontal velocity of 3 m/s. How far does the egg travel horizontally before hitting the ground? 1.5 m 3 m 5 m 15 m

3 m

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? 15 km/h 0.5 km/h 30 km/h 2 km/h

30 km/h

A ball freely falling at 20 m/s will in the next second have a speed of ______. 30 m/s 20 m/s 10 m/s. more than 30 m/s

30m/s

A ball is thrown vertically upward with an initial speed of 10 m/s, and it reaches a maximum height of 5 m. If the ball is thrown vertically with an initial speed of 30 m/s, what would its maximum height be? 15 m 30 m 45 m

45m

A ball is kicked so that initially its horizontal velocity is 5 m/s and its vertical velocity is 10 m/s. When the ball is at its highest point above the ground, what is its horizontal velocity? less than 5 m/s 5 m/s greater than 5 m/s

5 m/s

How far below a straight-line path does a horizontally projected projectile fall in the first second of fall? Depends on the projected speed 5 meters 10 meters Zero meters

5 meters

What exactly is meant by a "freely falling" object? An object in free fall falls under gravity alone with no friction. An object in free fall falls with constant speed. An object in free fall falls under gravity in air with air resistance but no other resistance. An object in free fall falls with constant velocity.

An object in free fall falls under gravity alone with no friction.

What does it mean to say something is in mechanical equilibrium? An object in mechanical equilibrium experiences a zero net force. An object in mechanical equilibrium experiences a net force twice its weight. An object in mechanical equilibrium must experience no forces. An object in mechanical equilibrium is always in motion.

An object in mechanical equilibrium experiences a zero net force.

Which force is greater, the Earth's pull on the Moon, or the Moon's pull on the Earth? Both pulls are the same. Earth's pull Moon's pull

Both pulls are the same.

A heavy crate is attached to the wall by a light rope, as shown in the figure. Another rope hangs off the opposite edge of the box. If you slowly increase the force on the free rope by pulling on it in a horizontal direction, which rope will break? Ignore friction and the mass of the ropes.

Both ropes are equally likely to break.

Why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn't change? The projectile has vertical inertia but not horizontal inertia. Air resistance can be ignored. The projectile has horizontal inertia but not vertical inertia. Gravity is a purely vertical force.

Gravity is a purely vertical force.

What are steps of the scientific method. Reasoning and derivation from axioms. Using Occam's razor to eliminate excess facts. Hypothesis, predictions, and experimental findings. Assembling and organizing facts and checking them against dogma.

Hypothesis, predictions, and experimental findings.

Give an example of what it means to say mass and weight are proportional to each other? If the mass doubles, then the weight stays the same. If the mass doubles, then the weight doubles, too. If the mass doubles, then the weight is cut in half. If the weight doubles, then the mass is cut in half.

If the mass doubles, then the weight doubles, too.

What did Galileo discover about moving bodies and force in his experiments with inclined planes? Bodies rolling down a steep inclined plane starting at a given height rolled up a gently inclined plane to a higher height. Bodies rolling up an inclined plane sped up. In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever. Bodies rolling down an inclined plane slowed down.

In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.

What is inertia? Inertia describes why it is easier to get a massive ball moving than it is to get a less massive one moving. Inertia explains why things stay in motion but not why they stay at rest. Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces. Inertia explains why things stay at rest but not why they stay in motion.

Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.

Fill in the blanks: Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____. Acceleration, inertia, action -reaction Inertia, acceleration, action -reaction Action, inertia, force Inertia, net force, friction

Inertia, acceleration, action -reaction

What type of path does a moving object follow in the absence of a force? It moves in a straight line and eventually slows to a stop. It follows a parabolic trajectory in the absence of a force. It follows a circular path in the absence of a force. It continues to move in a straight line at a constant speed.

It continues to move in a straight line at a constant speed.

A block of mass 2kg is acted upon by two forces: 3N3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion? It must be moving to the left. It must be moving to the right. It must be at rest. It could be moving to the left, moving to the right, or be instantaneously at rest.

It could be moving to the left, moving to the right, or be instantaneously at rest.

A stone is thrown upward at an angle. What happens to the magnitude of the vertical component of its velocity as it rises? As it falls? It increases while rising, but it decreases while falling. Rising or falling, it does not change. It decreases while rising and while falling. It decreases while rising, but it increases while falling.

It decreases while rising, but it increases while falling.

Which of Newton's three laws focuses on interactions? Newton's third law Newton's first law Newton's zeroth law Newton's second law

Newton's third law

If the mass of a sliding block is somehow tripled at the same time the net force on it is tripled, how does the resulting acceleration compare with the original acceleration? The acceleration is zero. The acceleration is reduced to 1/3 of its original value. The acceleration remains the same. The acceleration is tripled.

The acceleration remains the same.

f the net force acting on a sliding block is somehow tripled, what happens to the acceleration? The acceleration remains the same. The acceleration is zero. The acceleration triples. The acceleration is reduced to 1/3 its original value.

The acceleration triples.

Since movement of an object or system requires that a net force be applied to it, how can this occur if all action forces have opposite and equal reaction forces? Sometimes there are singular (unpaired) forces acting on an object. The action force doesn't act on the same object as the reaction force. Newton was never able to explain this.

The action force doesn't act on the same object as the reaction force.

If the cannon's recoil is the result of an equal and opposite reaction, why is the cannon's acceleration lower than the shell's acceleration? The cannon's acceleration is not lower than the shell's acceleration; it has the same acceleration as the shell. Not as much force is applied to it. The cannon has more mass than the shell.

The cannon has more mass than the shell.

What two principal factors affect the force of air resistance on a falling object? The force depends mostly on frontal area and speed. The force depends mostly on g and mass. The force depends mostly on mass and speed. The force depends mostly on mass and frontal area.

The force depends mostly on frontal area and speed.

In Lesson 3 of the tutorial, the horse is pulling a cart. What allows the horse to accelerate forward even though the cart is pulling back on the horse? The force of friction the ground exerts on the horse is larger than the force the cart is pulling back on the horse. The horse is pulling on the cart with a stronger force than the cart is pulling back on the horse. Friction from the ground on the horse is stronger than the sideways force the horse is exerting on the ground.

The force of friction the ground exerts on the horse is larger than the force the cart is pulling back on the horse.

As you increase your push on a stationary crate, will friction on the crate increase also? The friction force decreases and is in the opposite direction as your push. The friction force increases and is opposite in direction to your push. The friction force increases and is in the same direction as your push. The friction force remains zero.

The friction force increases and is opposite in direction to your push.

If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate? The frictional force has nothing to do with you pushing on the crate. The frictional force on the crate is 100 N opposite the direction of motion. The frictional force on the crate is 100 N in the same direction as the direction of motion. The frictional force on the crate is zero newtons.

The frictional force on the crate is 100 N opposite the direction of motion.

An object cannot remain at rest unless which of the following holds? The net force acting on it is zero. The net force acting on it is constant and nonzero. There are no forces at all acting on it. There is only one force acting on it.

The net force acting on it is zero.

What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance? The net forces are 14 N and 20 N, respectively. The net forces are 6 N and 10 N, respectively. The net forces are 6 N and 0 N, respectively. The net forces are 4 N and 0 N, respectively.

The net forces are 6 N and 0 N, respectively.

Why doesn't a heavy object accelerate more than a light object when both are freely falling? The larger air resistance force on the larger object makes it fall with the same acceleration. The ratio of the weight to mass is the same for all objects in the same locality. The inertia of the heavy object is just enough smaller than the inertia of the lighter object to counteract the larger gravity force. The inertia of the heavy object equals the inertia of the lighter object, so their accelerations are the same.

The ratio of the weight to mass is the same for all objects in the same locality.

Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force. The reaction force is the force due to compression inside the ball. The reaction force is zero because the force of the bat on the ball is equal and opposite to the force of the ball on the bat. The reaction force is the force by the ball on the bat. The reaction force is the force of the bat on the ball.

The reaction force is the force by the ball on the bat.

How many forces are required for an interaction? One force, an action, is needed for an interaction. Two forces, an action and a reaction, are needed for an interaction. One force, a reaction, is needed for an interaction. Two forces, a contact force and a friction force, are needed for an interaction.

Two forces, an action and a reaction, are needed for an interaction.

What is the condition for an object experiencing free fall? When gravity is the only force acting on an object, it is in free fall. When the net force on an object is zero, it is in free fall. When the net force on an object is equal and opposite to the gravity force, the object is in free fall. When there are no horizontal forces on an object, it is in free fall.

When gravity is the only force acting on an object, it is in free fall.

A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path? The bowling ball is not in equilibrium because the wood of the bowling alley exerts an upward force on the ball. The bowling ball is not in equilibrium because it is moving. The bowling ball is not in equilibrium because ΣF = -mg. Yes, the bowling ball is in equilibrium because ΣF = 0.

Yes, the bowling ball is in equilibrium because ΣF = 0.