?A rocket of mass 100,000 kg undergoes an acceleration of \(2 \mathrm{~m} /

Newton’s First Law of Motion State the law of inertia.

Newton’s First Law of Motion Is inertia a property of matter or a force of some kind?

Newton’s First Law of Motion What concept was missing from people’s minds in the 16th century when they couldn’t believe Earth was moving?

Newton’s First Law of Motion When a bird lets go of a branch and drops to the ground below, why doesn’t the moving Earth sweep away from the dropping bird?

Newton’s First Law of Motion What kind of path would the planets follow if suddenly their attraction to the Sun no longer existed?

Newton’s Second Law of Motion State Newton’s second law.

Newton’s Second Law of Motion Is acceleration directly or inversely proportional to force? Give an example.

Newton’s Second Law of Motion Is acceleration directly or inversely proportional to mass? Give an example.

Newton’s Second Law of Motion If the mass of a sliding block is tripled at the same time that the net force on it is tripled, how does the resulting acceleration compare to the original acceleration?

Newton’s Second Law of Motion What is the net force that acts on a 10-N freely falling object?

Newton’s Second Law of Motion Why doesn’t a heavy object accelerate more than a light object when both are freely falling?

Newton’s Second Law of Motion What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? 10 N of air resistance?

Newton’s Second Law of Motion What two principal factors affect the force of air resistance on a falling object?

Newton’s Second Law of Motion What is the acceleration of a falling object that has reached its terminal velocity?

Newton’s Second Law of Motion If two objects of the same size fall through air at different speeds, which encounters the greater air resistance?

Newton’s Second Law of Motion Why does a heavy parachutist fall faster than a lighter parachutist who wears the same size parachute?

Forces and Interactions Earlier in this chapter, we treated force as a push or pull; now we say it is part of an interaction. Is a force a push or pull, or part of an interaction?

Forces and Interactions How many forces are required for a single interaction?

Forces and Interactions When you push against a wall with your fingers, they bend because they experience a force. Identify this force.

Forces and Interactions A boxer can hit a heavy bag with great force. Why can’t he hit a sheet of tissue paper in midair with the same amount of force?

Newton’s Third Law of Motion State Newton’s third law.

Newton’s Third Law of Motion Consider hitting a baseball with a bat. If we call the force of the bat against the ball the action force, what is the reaction force?

Newton’s Third Law of Motion If the force that acts on a cannonball and the force that acts on the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and the cannon have very different accelerations?

Newton’s Third Law of Motion Is it correct to say that action and reaction forces always act on different bodies? Defend your answer.

Newton’s Third Law of Motion If body A and body B are both within a system, can forces between them affect the acceleration of the system?

Newton’s Third Law of Motion In terms of forces, what is necessary to accelerate a system?

Newton’s Third Law of Motion Identify the force that propels a rocket into space.

Newton’s Third Law of Motion How does a helicopter get its lifting force?

Newton’s Third Law of Motion To what law of physics do we refer when we say you cannot touch without being touched?

Summary of Newton’s Three Laws Which of Newton’s laws focuses on inertia? Which on acceleration? Which on action–reaction?

Write a letter to Grandma or Grandpa and tell her or him that Galileo introduced the concepts of acceleration and inertia, and was familiar with forces-but he didn’t see the connection among these three concepts. Tell how Isaac Newton did, and how the connection explains why heavy and light objects in free fall gain the same speed in the same time. In this letter, it’s okay to use an equation or two, as long as you make it clear that an equation is a shorthand notation of ideas you’ve explained.

The net force acting on an object and the resulting acceleration are always in the same direction. You can demonstrate this with a spool. If the spool is pulled horizontally to the right, in which direction will it roll?

Briefly, and carefully, hold your hand with the palm down like a flat wing outside the window of a moving automobile. Then slightly tilt the front edge of your hand upward and notice the lifting effect as air is deflected downward from the bottom of your hand. Can you see Newton’s laws at work?

If you drop a sheet of paper and a book side by side, not surprisingly the book falls faster than the paper. If you place the paper against the lower surface of the raised book and again drop them at the same time, they hit the floor at the same time. The book simply pushes the paper with it as it falls. Repeat, but with the paper on top of the book, and not sticking over its edge. How will the accelerations of the book and paper compare? Will these objects separate and fall differently? Or will they have the same acceleration? Try it and see! Then explain what happens.

Do these simple one-step calculations to familiarize yourself with the formulas that link the concepts of force, mass, and acceleration. Acceleration: \(a=\frac{F_{\text {net }}}{m}\) In Chapter 1 acceleration is defined as \(a=\frac{\Delta v}{\Delta t}\). that on an inclined plane, the acceleration of a cart that gains 6.0 m/s each 1.2 s is \(5.0 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: a=F_net/m a=delta v/delta t 5.0 m/s^2

In this chapter we learn that the cause of acceleration is given by Newton’s second law: \(a=\frac{F_{\text {net }}}{m}\).Show that the acceleration in Problem 35 results from a net force of 15 N exerted on a 3.0-kg cart. (Note: The unit N/kg is equivalent to \(\mathrm{m} / \mathrm{s}^{2}\).) Text Transcription: a=F_net/m m/s^2

Knowing that a 1-kg object weighs 10 N, confirm that the acceleration of a 1-kg stone in free fall is \(10 \mathrm{m} / \mathrm{s}^{2}\). Text Transcription: 10 m/s^2

A simple rearrangement of Newton’s second law gives \(F_{\text {net }}=m a\). Show that a net force of 84 N exerted on a 12-kg package is needed to produce an acceleration of \(7.0 \mathrm{~m} / \mathrm{s}^{2}\). (Note: The units \(\mathrm{kg} \cdot \mathrm{m} / \mathrm{s}^{2}\) and N are equivalent.) Text Transcription: F_net=ma 7.0 m/s^2 kg times m/s^2

A Honda Civic hybrid weighs about 2900 pounds. Calculate the weight of the car in newtons and its mass in kilograms. (FYI, 0.22 lb = 1 N; 1 kg on Earth’s surface has a weight of 10 N.)

When two horizontal forces are exerted on the car in Problem 39, 220 N forward and 180 N backward, the car undergoes acceleration. What additional force is needed to produce non-accelerated motion?

A 120-kg astronaut recedes from her spacecraft by activating a small propulsion unit attached to her back. The force generated by a spurt from this device is 30 N. Show that her acceleration is \(0.25 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: 0.25 m/s^2

Madison pushes with a 160-N horizontal force on a 20-kg crate of coffee resting on a warehouse floor. The force of friction on the crate is 80 N. Show that the acceleration is \(4.0 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: 4.0 m/s^2

Sophia pushes with a 40-N horizontal force on a 4.0-kg box resting on a lab bench. The box slides against a horizontal friction force of 24 N. Show that the box accelerates at \(4.0 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: 4.0 m/s^2

A business jet of mass 30,000 kg takes off when the thrust for each of two engines is 30,000 N. Show that its acceleration is \(2 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: 2 m/s^2

A rocket of mass 100,000 kg undergoes an acceleration of \(2 \mathrm{~m} / \mathrm{s}^{2}\). Show that the net force acting on it is 200,000 N. Text Transcription: 2 m/s^2

Calculate the horizontal force that must be applied to a 1-kg puck for it to accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.

Leroy, who has a mass of 100 kg, is skateboarding at 9.0 m/s when he smacks into a brick wall and comes to a dead stop in 0.2 s. (a) Show that his deceleration is \(45 \mathrm{~m} / \mathrm{s}^{2}\). (b) Show that the force of impact is 4500 N. (Ouch!) Text Transcription: 45 m/s^2

For 3.0 s, Allison exerts a net force of 10.0 N on a 6.7-kg shopping cart that was initially at rest. Find the acceleration of the cart, and show that it moves a distance of 6.7 m.

The heavyweight boxing champion of the world punches a sheet of paper in midair, bringing it from rest up to a speed of 25.0 m/s in 0.050 s. The mass of the paper is 0.003 kg. Show that the force of the punch on the paper is only 1.5 N.

Suzie Skydiver with her parachute has a mass of 50 kg. (a) Before opening her chute, what force of air resistance will she encounter when she reaches terminal velocity? (b) What force of air resistance will she encounter when she reaches a lower terminal velocity after the chute is open? (c) Discuss why your answers are the same or different.

If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40 N, how hard does the wall push on you? Show that if your mass is 80 kg, your acceleration is \(0.5 \mathrm{~m} / \mathrm{s}^{2}\) away from the wall. Text Transcription: 0.5 m/s^2

A force F acts in the forward direction on a cart of mass m. A friction force f opposes this motion. (a) Use Newton’s second law and show that the acceleration of the cart is \(\frac{F-f}{m}\). (b) Show that if the cart’s mass is 4.0 kg, the applied force is 12.0 N, and the friction force is 6.0 N, the cart’s acceleration is \(1.5 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: F-f/m 1.5 m/s^2

A firefighter of mass 80 kg slides down a vertical pole with an acceleration of \(4 \mathrm{~m} / \mathrm{s}^{2}\). Show that the friction force that acts on the firefighter is 480 N. Text Transcription: 4 m/s^2

A rock band’s tour bus, mass M, is accelerating away from a stop sign at rate a when a piece of heavy metal, mass M/5, falls onto the top of the bus and remains there. (a) Show that the bus’s acceleration is now \(\frac{5}{6} a\). (b) If the initial acceleration of the bus is \(1.2 \mathrm{~m} / \mathrm{s}^{2}\), show that when the bus carries the heavy metal with it, the acceleration will be \(1.0 \mathrm{~m} / \mathrm{s}^{2}\). Text Transcription: 1.2 m/s^2 1.0 m/s^2

Boxes of various masses are on a friction-free level table. (a) Rank, from greatest to least, the net forces on the boxes. (b) Rank, from greatest to least, the accelerations of the boxes

In cases A, B, and C, the crate is in equilibrium (no acceleration). Rank, from greatest to least, the amounts of friction between the crate and the floor in these three cases.

Consider a 100-kg box of tools in the locations A, B, and C. (a) Rank, from greatest to least, the masses of the 100-kg box of tools. (b) Rank, from greatest to least, the weights of the 100-kg box of tools.

Three parachutists, A, B, and C, have reached terminal velocity at the same altitude. (a) Rank their terminal velocities from fastest to slowest. (b) Rank the order of their reaching the ground from longest time to shortest time.

The strong man is pulled in the three situations shown. Rank, from least to greatest, the amount of tension in the rope in his right hand (the one attached to the tree in B and C).

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s First Law of Motion The Moon travels in a nearly circular path around Earth. If somehow gravitation between Earth and Moon disappeared, how would the Moon’s path differ?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s First Law of Motion To pull a wagon across a lawn at constant velocity, you must exert a steady force. Reconcile this fact with Newton’s first law, which states that motion at constant velocity indicates no force.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s First Law of Motion Your empty hand is not hurt when it bangs lightly against a wall. Why does your hand hurt when it bangs against the wall while carrying a heavy load? Which of Newton’s laws is most applicable?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s First Law of Motion Why is a massive cleaver more effective for chopping vegetables than a lighter knife of the same sharpness?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion Aristotle claimed that the speed of a falling object depends on its weight. We now know that all objects in free fall, whatever their weight, undergo the same rate of change in speed. Why does weight not affect acceleration?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion What is the net force acting on a 1-kg ball in free fall? What is the net force if it encounters 2 N of air resistance?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion As you leap upward from the ground, how does the force that you exert on the ground compare with your weight?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion “It’s not the fall that hurts you; it’s the sudden stop.” Translate this common saying into Newton’s laws of motion.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion For each of the following interactions, identify the action and reaction forces. (a) A hammer strikes a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion You hold an apple over your head. (a) Identify all the forces acting on the apple and their reaction forces. (b) When you drop the apple, identify all the forces acting on it as it falls, as well as the corresponding reaction forces.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion What is the net force on an apple that weighs 1 N when you hold it at rest above your head? What is the net force on the apple when you release it?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion Why does a cat that falls from the top of a 50-story building hit a safety net below no faster than it would if it fell from the 20th story?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion Free fall is motion in which gravity is the only force acting. (a) Explain why a skydiver who has reached terminal speed is not in free fall. (b) Explain why a satellite circling Earth above the atmosphere is in free fall.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion How does the weight of a falling body compare with the air resistance it encounters just before it reaches terminal velocity? Just after it reaches terminal velocity?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Second Law of Motion You tell your friend that the acceleration of a skydiver decreases as falling progresses. What is your response when your friend asks if this means the skydiver is slowing down?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions We know that Earth pulls on the Moon. Does it follow that the Moon also pulls on Earth?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions A friend says that Alé cannot push on the tree unless the tree pushes back on her, and another friend says that if Alé pushes quickly, the tree won’t push as hard on her. Which friend do you agree with, and why?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions Why can a boxer hit a heavy opponent harder for the same punch than she or he can hit a light opponent?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions When you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why does this force not move you upward?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions The strong man will push apart the two initially stationary freight cars of equal mass before he alone drops straight to the ground. Is it possible for him to give either of the cars a greater speed than the other? Why or why not?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Forces and Interactions Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the heavier cart roll compared with the lighter cart?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion Two 100-N weights are attached to a spring scale as shown. Does the scale read 0 N, 100 N, or 200 N, or some other reading? (Hint: Would the reading differ if one of the ropes were tied to the wall instead of to the hanging 100-N weight?)

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion When you rub your hands together, can you push harder on one hand than on the other?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion When the athlete holds the barbell overhead, the reaction force is the weight of the barbell on his hand. How is this force different when the barbell is lifted at an increasing speed?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion Consider the two forces acting on the person who stands still—namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they form an action–reaction pair? Why or why not?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion If a Mack truck and a motorcycle have a head-on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? Defend your answers.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion Two people of equal mass attempt a tug-of-war with a 12-m rope while standing on frictionless ice. When they pull on the rope, each person slides toward the other. How do their accelerations compare, and how far does each person slide before they meet?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion Suppose that one of the people in Exercise 87 has twice the mass of the other. How far does each person slide before they meet?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Newton’s Third Law of Motion Which team wins in a tug-of-war: the team that pulls harder on the rope, or the team that pushes harder against the ground? Explain.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws The photo shows Steve Hewitt and his daughter Gretchen. Is Gretchen touching her dad, or is he touching her? Explain.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws When your car moves along the highway at constant velocity, the net force on it is zero. Why, then, do you continue running your engine?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws The auto in the sketch moves forward as the brakes are applied. A bystander says that during the braking interval, the auto’s velocity and acceleration are in opposite directions. Do you agree or disagree?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws A racing car travels along a straight raceway at a constant velocity of 200 km/h. What horizontal forces act, and what is the net force acting on the car?

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws If it were not for air resistance, would it be dangerous to go outdoors on rainy days? Defend your answer.

Please do not be intimidated by the amount of end-of-chapter material in this and some other chapters. If your course work is to cover many chapters, your instructor is likely to assign only a few of each type of exercise. Summary of Newton’s Three Laws When you toss a coin upward, what happens to its velocity while it is ascending? What happens to its acceleration? (Neglect air resistance.) What is its acceleration at the top of its path?

Discuss whether or not a stick of dynamite contains force. Similarly, does a fist contain force? A hammer? Defend your answers.

In an orbiting space craft, you are handed two identical closed boxes, one filled with sand and the other filled with feathers. Discuss at least a couple of ways that you can tell which is which without opening the boxes.

Each of the vertebrae forming your spine is separated from its neighbors by discs of elastic tissue. Each step you take acts on your spine like a small jump. Can you think of a reason why you are a little shorter in the evening than you are in the morning? (Hint: Think about the hammerhead in Figure 2.2.)

Before the time of Galileo and Newton, many learned scholars thought that a stone dropped from the top of a tall mast on a moving ship would fall vertically and hit the deck behind the mast by a distance equal to how far the ship had moved forward during the time the stone was falling. In light of your understanding of Newton’s laws, what do you and your classmates think about this idea?

The opening photo in this chapter shows a favorite demonstration of author Paul Hewitt lying on his back with a blacksmith’s anvil placed on his chest. When assistant Will Maynez whacks the anvil with a strong sledgehammer blow, Hewitt is not injured. How is the physics here similar to that illustrated in Figure 1.8 (the girl with a stack of books on her head)?

Consider a ball at rest in the middle of a toy wagon. When the wagon is pulled forward, the ball rolls against the back of the wagon. A friend asks what force pushes the ball to the back of the wagon. Interpret this observation in terms of Newton’s first law.

If you’re in a car at rest that gets hit from behind, you can suffer a serious neck injury called whiplash. Discuss how whiplash involves Newton’s first law and why headrests are standard on today’s cars.

Why do you lurch forward in a bus that suddenly slows down? Why do you lurch backward when it picks up speed? What law applies here?

Suppose that you’re in a moving car and the engine stops running. You step on the brakes and slow the car to half speed. If you release your foot from the brakes, will the car spontaneously speed up a bit, or will it continue at half speed and slow due to friction? Defend your answer.

A rocket becomes progressively easier to accelerate as it travels through space. Why? (Hint: About 90% of the mass of a newly launched rocket is fuel.)

If you drop an object, its acceleration toward the ground is \(10 \mathrm{~m} / \mathrm{s}^{2}\). If you throw it down instead, would its acceleration after leaving your hand be greater than \(10 \mathrm{~m} / \mathrm{s}^{2}\)? Ignore air resistance. Why or why not? Text Transcription: 10 m/s^2

Can you think of a reason why the acceleration of the object thrown downward through the air in Exercise 106 would actually be less than \(10 \mathrm{~m} / \mathrm{s}^{2}\)? Text Transcription: 10 m/s^2

You throw a ball straight upward. Compared with its initial speed when thrown, how fast does it return to its starting point? Answer this for the case of no air resistance, and for the case where air resistance does affect motion.

A couple of your friends say that before a falling body reaches terminal velocity, it gains speed while acceleration decreases. Do you agree or disagree with your friends? Defend your answer.

How does the terminal speed of a parachutist before opening a parachute compare to the terminal speed after opening a parachute? Why is there a difference?

How does the gravitational force on a falling body compare with the air resistance it encounters before it reaches terminal velocity? After it reaches terminal velocity?

If and when Galileo dropped two balls from the top of the Leaning Tower of Pisa, air resistance was not really negligible. Assuming that both balls were the same size, yet one was much heavier than the other, which ball actually struck the ground first? Discuss your reasoning.

This is a scenario common to many physics students: You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn’t this mean that the forces cancel one another, making acceleration impossible? Resolve the misunderstanding underlying this question.

A farmer urges his horse to pull a wagon. The horse refuses, saying that to try would be futile, for it would flout Newton’s third law. The horse concludes that it can’t exert a greater force on the wagon than the wagon exerts on itself, so it wouldn’t be able to accelerate the wagon. What explanation can you offer to convince the horse to pull?

When Marie exerts a horizontal force of 200 N to slide a table across a floor at constant velocity, how much friction does the floor exert on the table? Is the force of friction equal and oppositely directed to her 200-N push? Does the force of friction make up the reaction force to her push? Why or why not?

Two equal-mass blocks are connected by a length of string. One block is placed at rest on a very smooth table, and the other block dangles off the table’s edge. You hold the blocks so they don’t move. When released, the hanging one accelerates downward, pulling the top block horizontally across the table. Why do both blocks undergo the same amount of acceleration? Show that this acceleration ideally is one-half g.

The bricks in this road were originally straight. Describe evidence for tires pushing the bricks in the wavy pattern, and explain why they do so.

Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne? Explain what does happen.

Can a dog wag its tail without the tail in turn “wagging the dog”? (Consider a dog with a relatively massive tail.)

If you simultaneously drop a pair of tennis balls from the top of a building, they strike the ground at the same time. If one of the tennis balls is filled with lead pellets, will it fall faster and hit the ground first? Which of the two will encounter more air resistance? Defend your answers.