Exam 1 Exercises Questions

Transcription

1 Exam 1 Exercises Questions Set 1 Exercise Questions Motion (Chapter 3) 1. A car starting from rest is speeding up with a constant acceleration of 5 m/s 2. (a) Draw a motion diagram using the particle model that shows her position at successive times and includes velocity and acceleration vectors. (b) How fast is the car moving after 5 seconds? 2. (a) Can an automobile with a velocity toward the north simultaneously have an acceleration toward the south? Explain. (b) Draw a motion diagram using the particle model that shows her position at successive times and includes velocity and acceleration vectors. 3. You are driving north on a highway. Then, without changing speed, you round a curve and drive east. (a) Do you accelerate? Explain. (b) Draw a motion diagram using the particle model that shows her position at successive times and includes velocity and acceleration vectors. 4. Cite an example of something with a constant speed that also has a varying velocity. Can you cite an example of something with a constant velocity and a varying speed? Defend your answers. 5. Someone standing at the edge of a cliff throws a ball nearly straight up at a certain speed and another ball nearly straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below? 6. A skydiver jumps out of an airplane. Her speed steadily increases until she deploys her parachute, at which point her speed quickly decreases. She subsequently falls to earth at a constant rate, stopping when she lands on the ground. Draw a motion diagram using the particle model that shows her position at successive times and includes velocity and acceleration vectors. Newton s 1 st Law (Chapter 2) 1. A hockey puck slides along the surface of the ice. If friction and air resistance are negligible, what force is required to keep the puck moving? 2. If you are squatting down (such as when you are examining the books on the bottom shelf in a library or bookstore) and suddenly get up, you can temporarily feel lightheaded. What do Newton s laws of motion have to say about why this happens? 3. In terms of Newton's first law (the law of inertia), how does a car headrest help to guard against whiplash in a rear-end collision? 4. Whiplash injuries during an automobile accident are caused by the inertia of the head. If someone is wearing a seatbelt, her body will tend to move with the car seat. However, her head is free to move until the neck restrains it, causing damage to the neck. Brain damage can also occur. The figure shows two sequences of head and neck motion for a passenger in an auto accident. One corresponds to a head-on collision, the other to a rear-end collision. Which is which? Explain 5. When a ball is tossed straight up, it momentarily comes to a stop at the top of its path. Is it in equilibrium during this brief moment? Why or why not? 6. When a car stops suddenly, the passengers tend to move forward relative to their sets. Why? When a car makes a sharp turn, the passengers tend to slide to one side of the car. Why? 1

2 Set 2 Exercise Questions Newton s 2 nd Law (Chapter 4) 1. A 4000-N bear grasping a vertical tree slides down at constant velocity. (i) Draw a force diagram of the bear. (ii) What is the friction force that acts on the bear? 2. Jose accelerates away from a stop sign. His eight-year-old daughter sits in the passenger seat. On whom does the back of the seat exert a greater force? 3. A racecar travels along a raceway at a constant velocity. What is the net force acting on the car? Now the racecar goes around a curve at a constant speed. What is the net force acting on the car now? Defend your answer. 4. Are the objects described here in static equilibrium, dynamic equilibrium, or not in equilibrium at all? a. A girder is lifted at constant speed by a crane. b. A girder is lowered by a crane. It is slowing down. c. You're straining to hold a 200 lb barbell over your head. d. A jet plane has reached its cruising speed and altitude. e. A rock is falling into the Grand Canyon. f. A box in the back of a truck doesn't slide as the truck stops. 5. A person can dive into water from a height of 10 m without injury, but a person who jumps off the roof of a 10-m-tall building and lands on a concrete street is likely to be seriously injured. Why is there a difference? 6. A rock is thrown upward. What is the net force acting on the rock at the top of its trajectory? What is the rock s acceleration at the top? 7. If you drop a pair of tennis balls (one filled with air and the other filled with lead pellets) simultaneously from the top of a building, will they strike the ground at the same time? Which one will experience greater air resistance? Defend your answers. Newton s 3 rd Law (Chapter 5) 1. For each of the following interactions, identify action and reaction forces. (i) A hammer hits a nail. (ii) Earth gravity pulls down on a book. (iii) A helicopter blade pushes air downward. 2. Why does a rope climber pull downward on the rope to move upward? 3. 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? 4. If you ask most people what force makes a car accelerate forward, they will say the force of the engine. But what force is directly responsible for making the car accelerate? 5. Josh and Taylor, standing face-to-face on frictionless ice, push off each other, causing each to slide backward. Josh is much bigger than Taylor. After the push, which of the two is moving faster? 6. A small compact car is pushing a large van that has broken down, and they travel along the road with equal velocities and accelerations. While the car is speeding up, is the force it exerts on the van larger than, smaller than, or the same magnitude as the force the van exerts on it? Which object, the car or the van, has the largest net force on it, or are the net forces the same? Explain. 2

3 Set 3 Exercise Questions Work and Energy Exercises (Chapter 7) 1. When a rifle with a longer barrel is fired, the force of expanding gases acts on the bullet for a longer distance. What effect does this have on the velocity of the emerging bullet? (Do you see why long-range cannons have such long barrels?) 2. You have a choice of catching a baseball or a bowling ball, both with the same KE. Which is safer (that is, which requires more work)? 3. Suppose that you and two classmates are discussing the design of a roller coaster. One classmate says that each summit must be lower than the previous one. Your other classmate says this is nonsense, for as long as the first one is the highest, it doesn't matter what height the others are. What do you say? Draw an energy bar diagram to help explain your answer. 4. You're on a rooftop and you throw one ball downward to the ground below and another upward with the same speed. Use conservation of energy to show that the speeds of both balls when they hit the ground is the same. Draw an energy bar diagram to help explain your answer. 5. Why cannot a Superball released from rest reach its original height when it bounces from a rigid floor? Draw an energy bar diagram to help explain your answer. Hint: you must account for heat energy. 6. Does a car burn more gasoline when its lights are turned on? Does the overall consumption of gasoline depend on whether or not the engine is running while the lights are on? Defend your answer. Atomic structure & properties of atoms (Chapter 11) 1. (i) Explain the role that the electric force plays in binding the atom together? (ii) Explain the role that the strong nuclear force plays in the nucleus? (iii) Why is a nuclear bomb really an electrical bomb? 2. The nuclear bomb (Fat Man) that was dropped over Nagasaki, Japan in 1945 used plutonium-239. Determine the number of protons, neutrons, electrons, energy levels, and if this form of the plutonium is the most common isotope? 3. To date the age of the earth (4.54 billion years old) geologist use radiometric (or radioactive) techniques. One technique is the lead-lead radioactive chain, which essentially compares lead ratios of 204 Pb, 206 Pb, 207 Pb, and 208 Pb. Which of these is the most common isotope of lead? Also, list the number of protons, neutrons, and energy levels. 4. Explain why the atom cannot look like the image to the right. 5. (i) Can two different elements contain the same total number of protons? If so, give an example. (ii) Can two different elements contain the same total number of neutrons? If so, explain your answer? 6. The atoms that compose your body are mostly empty space, and structures such as the chair you're sitting on are composed of atoms that are also mostly empty space. So why don't you fall through the chair? 3

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5 Set 4 Exercise Questions Gas Pressures (Chapter 14) 1. Explain how the Earth has an atmosphere? Why does the moon have no atmosphere? 2. If you buy a sealed bag of potato chips in Miami and drive with it to Denver, where the atmospheric pressure is lower, you will find that the bag gets very "puffy." Explain why. 3. Why is the pressure in an automobile's tires slightly greater after the car has been driven several kilometers? 4. What does pumping up a bike tire do to the tire s pressure? 5. Explain how a suction cup works? 6. Why is it so difficult to breathe when snorkeling at a depth of 1 m, and practically impossible at a 2-m depth? Why can't a diver simply breathe through a hose that extends to the surface? 7. Why does a helium balloon float upward in air? 5