How Things Work Practice Problems 1-2
A drag racer moves through the finish line at over 250 miles per hour and wins the race. A parachute opens and the drag racer slows to a stop. This happens because The air resistance of the parachute does negative work. The air resistance of the parachute does zero work. The air resistance of the parachute does positive work. The air resistance of the parachute is zero.
A
Any rotating object that is experiencing zero net torque will 1. continue rotating with constant angular momentum. gradually slow its rotation until it comes to a complete stop. gradually slow its rotation until it begins to reverse directions. gradually increase its rate of rotation.
A
During the winter Olympics a ski-jumper slides quickly down a long ramp and jumps into the air. Ignoring any affects due to the air, after leaving the ramp the acceleration of the ski-jumper is A. down B. up C. in the direction of his jump D. in the opposite direction to his velocity.
A
Homer Simpson is fighting a robot. When Homer punches the robot and exerts a force on it, 1. the robot pushes on Homer with an equal force. the robot pushes on Homer with less force, since Homer threw the first punch. the robot does not exert a force on Homer, since Homer punched the robot. the robot pushes back on Homer with more force, since the robot is made out of metal.
A
In the game "Twister" there is a spinner where a needle rotates clockwise at a constant angular velocity. The spinner lies flat down on the table as it is spinning. Using the right hand rule, what is the direction of the angular velocity? into the page. out of the page. to the left. to the right.
A
The moment of inertia of a long thin rod is smallest when it is spinning about an axis 1. down the center of the rod lengthwise. through the center of the rod, perpendicular to its length. through the end of the rod, perpendicular to its length. The moment of inertia is a constant, so the moment of inertia for cases A, B, and C are all equal.
A
When you drive in the mountains of West Virginia, there are some very steep downhill roads. On these roads you'll notice "runaway ramps" for trucks. If a truck's brakes fail, the driver can steer her truck onto one of these steep, uphill ramps. As the truck rolls up the ramp, it slows down because kinetic energy of the truck is converted into gravitational potential energy. the total force of gravity on the truck is stronger when the truck is on the runaway ramp. the total force of gravity on the truck is weaker when the truck is on the runaway ramp. there is always less snow on an uphill slope compared with a downhill slope.
A
You are holding a barbell (a heavy weight) motionless at chest height. You lift it high over your head and then lower it so that it is again motionless at chest height. The total work that you did on the barbell, from chest height to chest height, is 1. zero. twice the work required to lift it high over your head. half the work required to lift it high over your head. the same as the work required to lift it high over your head.
A
You are on a hayride: a horse-drawn cart with a flat top that is covered with hay. The cart has stopped to wait for a cow to cross the road and you have decided to stand up. Suddenly, the horse leaps forward and pulls the cart hard. Seconds later, you find yourself on the ground behind the cart because A. your inertia kept you motionless as the cart moved forward without you. B. your weight overcame the forward momentum you received from the cart. C. your energy was greater than your momentum and you accelerated too rapidly. D. the frictional force exerted on your feet by the cart was equal to your mass and they cancelled.
A
You have thrown a stone toward the pond in front of you and it is now at the highest point in its arc. Neglecting any forces due to air, the net force on the stone A. points straight downward. B. points down and forward. C. points straight forward. D. is zero.
A
Which of the following controls can cause an automobile to accelerate: the accelerator pedal, the brake pedal, and the steering wheel. A. only the accelerator pedal and the steering wheel. B. all three. C. only the accelerator pedal and the brake pedal. D. only the accelerator pedal.
B
To save space, you hang some shelves from the back of your door and fill them with objects. Neglecting friction or air resistance, these objects make it harder 1. for your door to swing, so that you must pull on it more strongly, even when it swings at constant angular velocity. to start your door swinging, but have no effect on its ability to continue swinging once started. for your door to remain motionless because these objects exert a torque on the door. for your door to be at equilibrium because these objects exert a weight on the door.
B
A car skids to a stop. What happens to its kinetic energy? 1. It turns into potential energy of the tires. It turns into thermal energy. It disappears without a trace. Nothing: the car still has it, but it is just inactive.
B
A child is riding in a wagon tied to the family dog with a string. As the dog walks steadily forward on the level sidewalk, the wagon follows perfectly. Suddenly the dog leaps forward to chase a squirrel and the string snaps. The loaded wagon breaks the string because the loaded wagon has such a large Answers: A. momentum. B. mass. C. weight. D. velocity.
B
A torque acting on an object will produce a 1. change in equilibrium. change in rotational motion. change in linear motion. change in center of gravity.
B
An arrow is heading toward its target after leaving the archer's bow. Neglecting any effects due to air, the net force on the arrow A. points directly forward. B. points directly downward C. points forward and downward. D. is exactly zero.
B
During a women's basketball game, Janelle and Iveta both go after the ball. They crash into each other, and Iveta falls to the ground while Janelle remains standing. From this we know 1. Janelle's force on Iveta was greater than the force that Iveta exerted on Janelle. Janelle's force on Iveta was equal to the force that Iveta exerted on Janelle. The net force that Iveta exerted on Janelle was zero. Janelle's force on Iveta was less than the force that Iveta exerted on Janelle
B
If you push a door directly towards the hinges (axis of rotation) the door won't open. The torque produced by that force is greater than zero. zero. less than zero. both positive and negative.
B
In an attempt to rob the stagecoach, the bandits pull out a nail gun that they stole from a construction site and nail the coach's wheels firmly to its frame. The wheels can no longer turn and the coach abruptly skids to a stop. What has become of the coach's kinetic energy? 1. It's now elastic potential energy in the nails. It's now thermal energy in the wheels and ground. It's now gravitational potential energy in the wheels. It's still present in the coach, as it must be because kinetic energy is conserved and can't be created or destroyed.
B
Power is always political. the rate at which work is done. the amount of work done. the rate at which kinetic energy is created
B
You are moving and need to lift several identical heavy boxes of books into a truck. The first box you lift directly into the back of the truck. The second box you slide up a ramp which has friction into the back of the truck. Which of the following statements is NOT true? A. The increase of potential energy is the same for box 1 and 2. B. You did the same amount of work to lift box 1 as to lift box 2 into the back of the truck. C. Friction does negative work on box 2. D. The kinetic energy of boxes 1 and 2 is zero while resting in the truck.
B
You are playing hockey with friends on a very large frozen pond. The hockey puck is at your feet motionless. You take a slap-shot with your hockey stick and the hockey puck goes zooming off at a high rate of speed sliding along the ice. The hockey puck eventually comes to a stop because A. there is no net forward force on the puck and so it will eventually slow down. B. friction between the puck and the ice will do enough negative work on the puck to equal the positive work done by you on the puck. C. friction between the puck and the ice will do more negative work on the puck than you did positive work on the puck. D. friction between the puck and the ice will do less negative work on the puck than you did positive work on the puck.
B
You are practicing shooting free throws at the basketball court. When you throw the ball, it travels in an arc toward the hoop. Ignoring any forces that air exerts on the ball, the net force on the ball just after it leaves you hand is A. down and away from you. B. straight down. C. zero. D. up and away from you.
B
You are seated at a table in the dining car on a train going to Washington DC. The train goes around a turn to the left, and you suddenly notice your drink sliding off to the right of you. The drink slides to the right because: 1. A. There is a force on it pushing it that way. B. The inertia of the glass wants to keep the drink moving in the same direction C. The acceleration is to the right, and so the drink moves that way. D. The coriolis force causes it to move to the right.
B
You are twirling a ball tied to the end of a string around your head. If the string breaks while the ball is directly to your right and moving forward, the ball will go: A. To the right. B. Straight ahead. C. Spiral outward. D. Spiral inward.
B
You hang your jacket on a coat hook in the hotel lobby and you hang your sweater on a coat hook inside the elevator. As the elevator is rising toward the penthouse suite, which coat hook is doing work on a garment? A. Neither coat hook is doing work on a garment. B. Only the coat hook in the elevator is doing work on a garment. C. Both coat hooks are doing work on garments. D. Only the coat hook in the lobby is doing work on a garment.
B
A speedboat is pulling a water-skier with a rope, exerting a large forward force on her. The skier is traveling forward in a straight-line path at a constant speed. The net force experienced by the skier is A. in the backward direction. B. in the forward direction. C. zero. D. in the upward direction.
C
A springboard diver leaps upward from the springboard, rises dramatically to a peak height, and than drops impressively into the water below the board. Neglect any influences of air or the atmosphere. During this trip, the diver experiences A. an upward net force that gradually diminishes to zero at the peak height and then becomes a downward net force. B. a constant upward net force on the way up and a constant downward net force on the way down. C. a constant downward net force. D. a downward net force that is proportional to the diver s height above the water.
C
A whiffle ball and a baseball are exactly the same size, but the baseball weighs considerably more. If you drop a whiffle ball and a baseball exactly at the same time from the 2nd floor balcony of your apartment, the baseball will hit the ground first. This happens because The baseball weighs more than the whiffle ball. The air resistance of the whiffle ball is larger. The air resistance of the whiffle ball is the same as the baseball, but mass of the whiffle ball is smaller. The air resistance of the baseball is larger than the whiffle ball, but the mass of the baseball is larger.
C
After reaching the top of the lift-hill on a roller-coaster, the chain releases and you zoom down a long hill which ends at the beginning of the loop-the-loop. You zoom around the loop-the-loop going upside down in the process. What is TRUE about the loop-the-loop: A. Your velocity at the bottom is equal to the velocity at the top of the loop-the-loop. B. Your velocity at the bottom is less than the velocity at the top of the loop-the-loop. C. Your velocity at the bottom is greater than the velocity at the top of the loop-the-loop. D. You velocity at the top of the loop-the-loop is zero.
C
Combining business and pleasure, you are taking a balloon ride to the office. You hold your briefcase firmly in your hand as the balloon rises upward at constant velocity. During this ascent, you are doing 1. work on the briefcase but the balloon is doing zero work on you. zero work on the briefcase but the balloon is doing work on you. work on the briefcase and the balloon is doing work on you. zero work on the briefcase and the balloon is doing zero work on you.
C
Mike and Johnny are in trouble for scuffling in the school cafeteria. While Mike admits that he pushed Johnny, who immediately fell over backward, Mike claims that Johnny pushed back and is thus just as guilty. From the perspective of physics, A. Johnny pushed back on Mike, but with less force than Mike exerted on him. B. Johnny pushed back on Mike, but with more force than Mike exerted on him. C. Johnny did push back on Mike, with exactly the same amount of force as Mike exerted on him. D. Johnny didn't push back on Mike.
C
The Kinetic Energy is equal to the force times the distance. equal to the height above the ground. the form of energy contained in an object's motion. gravitational potential energy.
C
Two identical balls roll off a horizontal desk at exactly the same moment. One ball is traveling horizontally twice as fast as the other at the moment the two leave the desk. Compared to the slower ball, the faster ball hits the ground at the same time and same horizontal distance from the desk. later, and at four times the horizontal distance from the desk. at the same time, but at twice the horizontal distance from the desk. earlier, but at the same horizontal distance from the desk.
C
Which of the following objects is definitely accelerating? A. A person who is riding an up escalator midway between floors. B. A person who is riding a down elevator, midway between floors. C. A ball that was tossed straight up and is now motionless at its peak height. D. A car heading north on a straight, level road at 60 mph.
C
While you are changing your tire, you take out your wrench and attempt to take off a lug nut so as to remove the tire. Try as hard as you can you can't turn the nut. The net torque on the nut is either clockwise or counterclockwise, depending on whether you are in the northern or southern hemisphere. counterclockwise. zero. clockwise.
C
You are carrying your book-bag and riding a bus up a long hill at a constant velocity. Which of the following is NOT true: A. The NET force on you is zero. B. The bus is doing positive work on you. C. You are doing zero work on your book-bag D. Your total mechanical energy (kinetic + potential) is increasing.
C
You are trying to loosen an ordinary screw that someone has jammed into your dormitory wall. Try as you may, you can't get that screw to turn at all. While you are twisting as hard as possible on the head of the screw, the net torque that the screw is experiencing is either clockwise or counterclockwise, depending on whether you are in the northern or southern hemisphere. counterclockwise. zero. clockwise
C
You come home from the grocery store with two gallons of milk and put them away into the shelves built into the swinging door very close to the end which opens. You notice that it takes quite a bit of force to open the refrigerator door. If you put the two gallons of milk as close as possible to the hinges of the door, the door will still be hard to open, since the mass of the door is the same. the door will be harder to open (you need more torque), since the rotational mass (moment of inertia) increases the door will be easier to open (you need less torque), since the rotational mass (moment of inertia) decreases. the door will be easier to open (you need less torque), since the mass of the door is less.
C
You get a flat tire on your car coming to school. Trying as hard as you can to rotate the wrench counterclockwise to remove the nut, it won't move. As you pull on the wrench, the NET torque on the nut is 1. clockwise counterclockwise zero huge
C
Your car breaks down and comes to a stop. You get your friend to steer the car while you push it to the side of the road. While you are pushing the car, A. you are pushing the car with a larger force than the car pushes back on you. B. you are pushing the car with a smaller force than the car pushes back on you C. you are pushing the car with a force which is equal in amount to the force the car pushes back on you. D. you are pushing the car with a force only slightly larger than the car pushes back on you.
C
A circular saw uses a spinning, circular blade to cut through wood. When you start the motor, it applies a constant torque and spins up the blade to its full angular velocity in 2 seconds. If you change the blade for one with three times the moment of inertia, how long with the motor now take to spin up the blade? 1. 2/3 seconds 1 second 2 seconds 6 seconds
D
A fast-moving softball is heading directly toward the pitcher after being hit by the batter. As it travels forward, the softball is experiencing A. a forward force that is equal to its momentum. B. a forward force that is equal to the square root of its momentum. C. a forward force that is equal to 1 divided by its momentum. D. zero forward force.
D
A gymnast bounces upward from a trampoline, then falls back. During the time she is airborne, A. her velocity is a constant on the way up, and the way down. Only the direction of the velocity changes. B. her velocity changes, and there is no acceleration. C. both her velocity and her acceleration changes from up to down. D. her velocity changes and her acceleration is downward
D
A heavy statue rests motionless on the floor. The statue is experiencing its weight downward and an equally strong force upward from the floor. We know that these two forces on the statue are equal in amount but oppositely directed because A. for every action, there is an equal but oppositely directed reaction. B. the statue has zero velocity. C. Newton s third law requires that forces always appear in equal but oppositely directed pairs. D. the statue is not accelerating so the two forces must sum to zero.
D
A heavy statue rests motionless on the floor. The statue is experiencing its weight downward and an equally strong force upward from the floor. We know that these two forces on the statue are equal in amount but oppositely directed because A. for every action, there is an equal but oppositely directed reaction. B. the statue has zero velocity. C. Newton s third law requires that forces always appear in equal but oppositely directed pairs. D. the statue is not accelerating so the two forces must sum to zero.
D
A heavy vase rests motionless on the floor. The vase is experiencing its weight downward and an equally strong force upward from the floor. We know that these two forces on the vase are equal in amount but oppositely directed because A. for every action, there is an equal but oppositely directed reaction. B. the vase has zero velocity. C. Newton's third law requires that forces always appear in equal but oppositely directed pairs. D. the vase is not accelerating so the two forces must sum to zero.
D
A volleyball player has just served the ball. As the ball travels forward horizontally through the air and neglecting air resistance, the volleyball is experiencing A. a forward force that is equal to its inertia. B. a forward force that is equal to its mass. C. a forward force that is equal to its momentum. D. zero forward force.
D
As your friend is driving, you sit in the passenger seat tossing your keys up into the air. Just as they leave your hand, your friend slams onto the breaks for a red light. Your keys slam into the dash board because A. there is a centrifugal force on the keys. B. there is a magnet in the dashboard C. the brakes apply a force to the keys D. the inertia of the keys wants them to keep moving with the speed of the car.
D
If a box is sliding down a ramp at WalMart starts with 500 J of potential energy and it ends up with a kinetic energy of 450 J at the bottom of the ramp, what do you know about this situation? A. The box's potential energy was completely converted into kinetic energy. B. The box had a constant mechanical energy. C. . The box gained more kinetic energy than it had in potential energy. D. The box lost some of its mechanical energy to thermal energy (friction).
D
If you push against a heavy bookshelf but it remains in place, it experiences static friction with the floor. If the bookshelf begins to slide as you push on it, it experiences sliding friction with the floor. Friction removes energy from the bookshelf 1. only when it remains in place. only when you lift the bookshelf off the floor, not when you move it horizontally. both when it remains in place and when it's sliding across the floor. only when it's sliding across the floor.
D
When you first throw a bowling ball onto a bowling lane, the ball slides without spinning. The ball gradually begins to spin because 1. you throw the ball with your right hand and it has to obey the right-hand rule. the ball is political and spin is everything in politics. the force of the ball's momentum is transformed into angular momentum and rotational speed. sliding friction produces a torque on the ball, so that the ball undergoes angular acceleration.
D
Which of the following is NOT accelerating? A race car driving around a circular track at constant speed. A bicyclist stopping at an intersection. A diver who has just leaped off the diving board and is in midair. A child riding an escalator up to the second floor at constant velocity.
D
You are holding your friend s new television motionless in your hands while she fumbles in her purse for the keys to her apartment. Beads of sweat are dripping down your face. While you stand there like this, you are A. doing negative work on the television and it is doing (positive) work on you. B. doing (positive) work on the television. C. doing negative work on the television and it is doing negative work on you. D. doing zero work on the television.
D
You are rearranging the furniture and are moving your desk to the other side of the room. To keep your desk sliding across the level floor at constant velocity, you have to keep pushing it forward. The net force on the desk is A. forward and proportional to the velocity at which the desk is moving. B. forward because the forward force you are exerting on the desk is larger than the backward force that friction is exerting on the desk. C. forward and proportional to the speed at which the desk is moving. D. zero, even though the ground is exerting a backward frictional force on the desk.
D
You are standing at the top of a tall cliff above a calm lake. You have two stones in your hand, one twice as heavy as the other, and you throw them together horizontally at the same speed. Both stones soon hit the water. Neglecting any air resistance, the heavier stone reaches the water in half the time and half as far from the cliff as the lighter stone. in half the time but at the same place as the lighter stone. at the same time but half as far from the cliff as the lighter stone. at the same time and at the same place as the lighter stone.
D
You are standing still in an elevator, with a briefcase hanging from your motionless hand. As the elevator rises toward the top of the building, you are doing 1. zero work on the briefcase and the elevator is doing zero work on you. (positive) work on the briefcase and the elevator is zero work on you. zero work on the briefcase and the elevator is doing (positive) work on you. (positive) work on the briefcase and the elevator is doing (positive) work on you.
D
You are watching a child is flying a kite at the park. The kite is hovering motionless in the sky, about 100m above the ground. The wind is blowing smoothly toward the east. The net force on the kite is A. in the upward direction. B. toward the west. C. toward the east. D. zero.
D
You push a large heavy filing cabinet across the floor of your new office at a constant velocity. You are exerting a constant force against the filing cabinet. You are doing positive work. You are doing zero work. You are doing negative work. You are doing positive work, and friction is doing negative work
D