Exam 2 Conceptual Questions
A cart (weight w1) is attached by a lightweight cable to a bucket (weight w2) as shown. The ramp is frictionless. When released, the cart accelerates up the ramp. Which of the following is a correct free-body diagram for the cart? images needed
images needed
Which of the following statements about centripetal acceleration is true? (a)An object moving at a constant velocity cannot have a centripetal acceleration. (b)An object moving at a constant speed may have a centripetal acceleration
(a)An object moving at a constant velocity cannot have a centripetal acceleration. (b)An object moving at a constant speed may have a centripetal acceleration.
The car in the drawing is moving clockwise around a circular section of road at a constant speed. What are the directions of its velocity and acceleration at (a) position 1 and (b) position 2? Specify your responses as north, east, south, or west.
(a)The velocity is due south and the acceleration is due west. (b)The velocity is due west and the acceleration is due north.
Would a change in the earth's mass affect (a)the banking of airplanes as they turn, (b)the banking of roadbeds, (c)the speeds with which satellites are put into circular orbits, and (d)the performance of the loop-the-loop motorcycle stunt?
(a)the banking of airplanes as they turn, (b)the banking of roadbeds, (c)the speeds with which satellites are put into circular orbits, and (d)the performance of the loop-the-loop motorcycle stunt?
Two satellites are placed in orbit, one about Mars and the other about Jupiter, such that the orbital speeds are the same. Mars has the smaller mass. Is the radius of the satellite in orbit about Mars less than, greater than, or equal to the radius of the satellite orbiting Jupiter?
less than
A rocket is at rest on the launch pad. When the rocket is launched, its kinetic energy increases. Consider all of the forces acting on the rocket during the launch, and decide whether the following statement is true or false: The amount by which the kinetic energy of the rocket increases during the launch is equal to the work done by the force generated by the rocket's engine.
no
A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat?
no
An airplane is flying horizontally with a constant momentum during a time interval delta t . Is there a net impulse acting on the plane during this time? Use the impulse-momentum theorem to guide your thinking.
no
An ice boat is coasting on a frozen lake. Friction between the ice and the boat is negligible, and so is air resistance. Nothing is propelling the boat. From a bridge someone jumps straight down into the boat, which continues to coast straight ahead. (a) Does the total horizontal momentum of the boat plus the jumper change?
no
An object slides along the surface of the earth and slows down because of kinetic friction. If the object alone is considered as the system, the kinetic frictional force must be identified as an external force that, according to Equation 7.4, decreases the momentum of the system. (a) If both the object and the earth are considered to be the system, is the force of kinetic friction still an external force
no
An object slides along the surface of the earth and slows down because of kinetic friction. If the object alone is considered as the system, the kinetic frictional force must be identified as an external force that, according to Equation 7.4, decreases the momentum of the system. (b) Can the frictional force change the total linear momentum of the two-body system?
no
Two identical automobiles have the same speed, one traveling east and one traveling west. Do these cars have the same momentum?
no
The energy released by the exploding gunpowder in a cannon propels the cannonball forward. Simultaneously, the cannon recoils. The mass of the cannonball is less than that of the cannon. Which has the greater kinetic energy, the launched cannonball or the recoiling cannon? Assume that momentum conservation applies.
the cannonball
Consider two people, one on the earth's surface at the equator and the other at the north pole. Which has the larger centripetal acceleration?
the person at the equator, because they have a smaller radius
What is the chance of a light car safely rounding an unbanked curve on an icy road as compared to that of a heavy car: worse, the same, or better? Assume that both cars have the same speed and are equipped with identical tires.
the same
A box has a weight of 150 N and is being pulled across a horizontal floor by a force that has a magnitude of 110 N. The pulling force can point horizontally, or it can point above the horizontal at an angle . When the pulling force points horizontally, the kinetic frictional force acting on the box is twice as large as when the pulling force points at the angle . Find .
43 degrees
An object is thrown up in the air. Is the object in momentary equilibrium when it reaches its highest point? A. No, never. B. Yes, always. C. Yes, but only if we can ignore air resistance. D. Yes, but only if it is thrown straight up (i.e. no horizontal component to 𝒗). E. Misleading question; impossible to tell.
A (No, never)
A vehicle designed for exploring the moon's surface is being tested on earth, where it weighs roughly six times more than it will on the moon. The acceleration of the vehicle along the ground is measured. To achieve the same acceleration on the moon, will the required net force be (a) the same as, (b) greater than, or (c) less than that on earth?
A (The net force (sigma F) required to accelerate the vehicle is specified by Newton's second law as , (sigma F = ma) where (m) is the vehicle's mass and (a) is the acceleration. For a given acceleration, the net force depends only on the mass, which is the same on the moon as it is on the earth. Therefore, the required net force is the same on the moon as it is on the earth.)
A tractor driving at a constant speed pulls a sled loaded with firewood. There is friction between the sled and the road. The total work done on the sled after it has moved a distance d is A. Zero. B. Negative. C. Positive. D. Two of A, B, and C, depending on circumstances. E. Three of A, B, and C, depending on circumstances.
A (Zero)
A box is sitting in the back of truck. The truck begins to accelerate forward (to the right) and the box does not slip. In a free-body diagram for the box, the force of friction on the box points A. to the right. B. to the left. C. up. D. depends on the value of the coefficient of friction. E. not enough information to decide.
A (to the right)
You press your physics book flat against a vertical wall with your hand. Your arm remains horizontal. What is the direction of the friction force exerted by the wall on the book? A. upward B. downward C. out from the wall D. into the wall E. misleading question; there is no friction
A (upward)
(a)Can a single object have a kinetic energy but no momentum? (b)Can a group of two or more objects have a total kinetic energy that is not zero but a total momentum that is zero
B (Can a group of two or more objects have a total kinetic energy that is not zero but a total momentum that is zero?)
An elevator is being lifted at a constant speed by a steel cable attached to an electric motor. Which statement is correct? A. The cable does positive work on the elevator, and the elevator does positive work on the cable. B. The cable does positive work on the elevator, and the elevator does negative work on the cable. C. The cable does negative work on the elevator, and the elevator does positive work on the cable. D. The cable does negative work on the elevator, and the elevator does negative work on the cable. E. None of the above.
B (The cable does positive work on the elevator, and the elevator does negative work on the cable)
A piece of fruit falls straight down. As it falls, the A. gravitational force does positive work on it and the gravitational potential energy increases. B. gravitational force does positive work on it and the gravitational potential energy decreases. C. gravitational force does negative work on it and the gravitational potential energy increases. D. gravitational force does negative work on it and the gravitational potential energy decreases. E. answer depends on whether or not air resistance is present.
B (gravitational force does positive work on it and the gravitational potential energy decreases)
A block of mass m is placed at rest on a frictionless incline of angle θ. It is released and slides a distance s along the incline before reaching the floor. The floor exerts a kinetic friction force f on the block. After reaching the floor the block slides a distance x (different from s) and stops. The net work done on the block during its entire motion is A. positive. B. zero. C. negative. D. either positive or negative, depending on the value of f. E. either positive, negative, or zero, depending on the value of f.
B (zero)
Block A on the left has mass 1.00 kg. Block B on the right has mass 3.00 kg. Block A is initially moving to the right at 6.00 m/s, while block B is initially at rest. The surface they move on is level and frictionless. What is the velocity of the center of mass of the two blocks before the blocks collide? A. 6.00 m/s, to the right B. 3.00 m/s, to the right C. 1.50 m/s, to the right D. zero E. Not enough information is given to decide.
C (1.50 m/s, to the right)
A cable attached to a car holds the car at rest on the frictionless ramp (angle ). The ramp exerts a normal force on the car. How does the magnitude Fn of the normal force compare to the weight w of the car? A. Fn = w B. Fn > w C. Fn < w D. Two of these are possible, depending on the value of alpha . E. All three of these are possible, depending on the value of alpha
C (Fn < w)
Suppose two objects collide head on, as in Example 7, where initially object 1 (mass = m1) is moving and object 2 (mass= m2) is stationary. Now assume that they have the same mass, so m1 = m2. Which one of the following statements is true? (a)Both objects have the same velocity (magnitude and direction) after the collision. (b)Object 1 rebounds with one-half its initial speed, while object 2 moves to the right, with one-half the speed that object 1 had before the collision. (c)Object 1 stops completely, while object 2 acquires the same velocity (magnitude and direction) that object 1 had before the collision.
C (Object 1 stops completely, while object 2 acquires the same velocity (magnitude and direction) that object 1 had before the collision.)
You are testing a new car using crash test dummies. Consider two ways to slow the car from 90 km/h (56 mi/h) to a complete stop: (i) You let the car slam into a wall, bringing it to a sudden stop. (ii) You let the car plow into a giant tub of gelatin so that it comes to a gradual halt. In which case is there a greater impulse of the net force on the car? A. In case (i). B. In case (ii). C. The impulse is the same in both cases. D. The answer depends on how rigid the front of the car is. E. The answer depends on how rigid the front of the car is and on the mass of the car.
C (The impulse is the same in both case)
You throw a ball straight up into the air. At the same time, your friend drops an identical ball from the same height above the ground at which you throw yours. Ignoring air resistance, throughout the motion of both balls, the change in kinetic energy of your ball is A. Less than that of your friend's ball B. Greater than the of your friend's ball C. The same as that of your friend's ball D. Any of the above depending on the initial speed of your ball E. Not enough information to decide
C (The same as that of your friend's ball)
Assuming a circular orbit, the work done by the gravitational force exerted on the Earth by the Sun during a short time interval in which the Earth moves through a displacement in its orbital path is A. Positive. B. Negative. C. Zero. D. Sometimes positive and sometimes negative depending on the time of year E. Impossible to tell.
C (Zero.)
The mass of the moon is 1/87 of the mass of the earth. Compared to the gravitational force that the earth exerts on the moon, the gravitational fore that the moon exerts on the earth is A. 812 = 6561 times greater. B. 81 times greater. C. equally strong. D. 1/81 as great. E. (1/81)2 = 1/6561 as great.
C (equally strong.)
You drive a race car around a circular track of radius R at a constant speed of v. If you then drive the same car around a different circular track of radius 2R at a constant speed of 2v, your acceleration will be A. eight times greater. B. four times greater. C. twice as great. D. the same. E. half as great.
C (twice as great)
Consider the following systems: 1) A ball is dropped from the top of a building. The system is the ball. 2) A ball is dropped from the top of a building. The system is the ball and the earth. 3) A billiard ball collides with a stationary ball on a frictionless surface. The system is the moving ball. 4) A space probe is moving in deep space where gravitational and other forces are negligible. The system is the space probe. Which of the systems are isolated systems? A) 1 B) 2 C) 1 & 3 D) 2 & 4 E) none
D (2 & 4)
Compared to the earth, a distant planet has twice the mass and twice the radius. This means that compared to the earth's surface gravity, the surface gravity on the other planet is A. four times as much. B. twice as much. C. the same. D. half as much. E. one-quarter as much.
D (half as much)
The work done by a conservative force is indicated in the figure below for several different paths connecting points A and B. What is the work done by this force on Path 1? A. 3 J B. -33J C. 33 J D. -3 J E. 7 J
D (need to look at a pic)
Two blocks are connected as shown. When released, the 6.00- kg block accelerates downward and the 8.00-kg block accelerates to the right. After each block has moved 2.00 cm, the force of gravity has done A. work on both blocks, but more work on the 8.00-kg block than on the 6.00-kg block. B. the same amount of work on both blocks. C. work on both blocks, but less work on the 8.00-kg block than on the 6.00-kg block. D. work on the 6.00-kg block only. E. Not enough information is given to decide
D (work on the 6.00-kg block only)
Object 1 and Object 2 have equal kinetic energies. How do the magnitudes of their momenta, p1 and p2, compare? A.𝑝 <𝑝 12 B. 𝑝 > 𝑝 12 C. 𝑝 = 𝑝 12 D. p1/p2 = square root (k1/k2), where K is the kinetic energy E. Not enough information to decide.
E (Not enough information to decide)
Two iceboats (one of mass m, one of mass 2m) hold a race on a frictionless, horizontal, frozen lake. Both iceboats start at rest, and the wind exerts the same constant force on both iceboats. Which iceboat crosses the finish line with more kinetic energy (KE)? A. The iceboat of mass m: it has twice as much KE as the other. B. The iceboat of mass m: it has four times as much KE as the other. C. The iceboat of mass 2m: it has twice as much KE as the other. D. The iceboat of mass 2m: it has four times as much KE as the other. E. They both cross the finish line with the same kinetic energy.
E (They both cross the finish line with the same kinetic energy)
The work done by a conservative force is indicated in the figure below for several different paths connecting points A and B. What is the work done by this force on Path 2? A. 18 J B. 26J C. -26 J D. 4 J E. -4 J
E (need to look at a pic)
The earth is a satellite of the sun. Suppose the sun were to shrink to half of its present radius while maintaining the same mass. What effect would this have on the radius r and the period T of the earth's orbit around the sun? A. r would decrease and T would decrease. B. r would increase and T would increase. C. r would decrease and T would increase. D. r would increase and T would decrease. E. r and T would both be unchanged.
E (r and T would both be unchanged.)
A stack of books whose true weight is 165 N is placed on a scale in an elevator. The scale reads 165 N. From this information alone, can you tell whether the elevator is moving with a constant velocity of 2 m/s upward, is moving with a constant velocity of 2 m/s downward, or is at rest?
No, all you can tell is if it accelerates or decelerates
A crate hangs from a ring at the middle of a rope, as the drawing illustrates. A person is pulling on the right end of the rope to keep the crate in equilibrium. Can the rope ever be made to be perfectly horizontal?
No, because there must always be a vertical (upward) component of the tension force in the rope to balance the weight of the crate.
In the horizontal direction, both the thrust generated by the engines and air resistance act on the plane. Considering your answer to part a, how is the impulse of the thrust related (in magnitude and direction) to the impulse of the force due to the air resistance?
The impulse of the thrust is equal in magnitude and opposite in direction to the impulse of the force due to air resistance.
In Times Square in New York City, people celebrate on New Year's Eve. Some just stand around, but many move about randomly. Consider a group consisting of all of these people. Approximately, what is the total linear momentum of this group at any given instant?
The total linear momentum is approximately zero because of the random directions and random speeds of the moving people.
A person has a choice of either pushing or pulling a sled at a constant velocity, as the drawing illustrates. Friction is present. If the angle is the same in both cases, does it require less force to push or to pull the sled?
To pull, because the upward component of the pulling force reduces the normal force and, therefore, also reduces the force of kinetic friction acting on the sled.
Object A weighs twice as much as object B at the same spot on the earth. Would the same be true at a given spot on Mars?
Yes, because the ratio of the two weights depends only on the masses of the objects, which are the same on the earth and on Mars.
A 10-kg suitcase is placed on a scale that is in an elevator. In which direction is the elevator accelerating when the scale reads 75 N and when it reads 120 N? (a)Downward when it reads 75 N and upward when it reads 120 N (b)Upward when it reads 75 N and downward when it reads 120 N (c)Downward in both cases (d)Upward in both cases
a (Downward when it reads 75 N and upward when it reads 120 N)
Engine A has a greater power rating than engine B. Which one of the following statements correctly describes the abilities of these engines to do work? (a)Engines A and B can do the same amount of work, but engine A can do it more quickly. (b)Engines A and B can do the same amount of work in the same amount of time. (c)In the same amount of time, engine B can do more work than engine A.
a (Engines A and B can do the same amount of work, but engine A can do it more quickly)
In a simulation on earth, an astronaut in his space suit climbs up a vertical ladder. On the moon, the same astronaut makes the exact same climb. Which one of the following statements correctly describes how the gravitational potential energy of the astronaut changes during the climb? (a)It changes by a greater amount on the earth. (b)It changes by a greater amount on the moon. (c)The change is the same in both cases.
a (It changes by a greater amount on the earth)
Three particles have identical masses. Each particle experiences only the gravitational forces due to the other two particles. How should the particles be arranged so each one experiences a net gravitational force that has the same magnitude? (a)On the corners of an equilateral triangle (b)On three of the four corners of a square (c)On the corners of a right triangle
a (On the corners of an equilateral triangle)
In which one of the following situations could an object possibly be in equilibrium? (a)Three forces act on the object; the forces all point along the same line but may have different directions. (b)Two perpendicular forces act on the object. (c)A single force acts on the object. (d)In none of the situations described in (a), (b), and (c) could the object possibly be in equilibrium.
a (Three forces act on the object; the forces all point along the same line but may have different directions)
A suitcase is hanging straight down from your hand as you ride an escalator. Your hand exerts a force on the suitcase, and this force does work. This work is (a)positive when you ride up and negative when you ride down, (b)negative when you ride up and positive when you ride down, (c)positive when you ride up or down, (d)negative when you ride up or down.
a (positive when you ride up and negative when you ride down)
A rope is used in a tug-of-war between two teams of five people each. Both teams are equally strong, so neither team wins. An identical rope is tied to a tree, and the same ten people pull just as hard on the loose end as they did in the contest. In both cases, the people pull steadily with no jerking. Which rope sustains the greater tension, (a)the rope tied to the tree (b)the rope in the tug-of-war (c)do the ropes sustain the same tension?
a (the rope tied to the tree)
Two objects have the same momentum. Do the velocities of these objects necessarily have (a)the same directions (b)the same magnitudes
a (the same directions)
A car is traveling in uniform circular motion on a section of road whose radius is (see the drawing). The road is slippery, and the car is just on the verge of sliding. a.) if the car's speed were doubled, what would be the smallest radius at which the car does not slide? Express your answer in terms of . (b) What would be your answer to part (a) if the car were replaced by one that weighed twice as much, the car's speed still being doubled?
a.) 4r b.) 4r
The acceleration due to gravity on the moon is one-sixth that on earth. (a) Is the true weight of a person on the moon less than, greater than, or equal to the true weight of the same person on earth? (b) Is the apparent weight of a person in orbit about the moon less than, greater than, or equal to the apparent weight of the same person in orbit about the earth?
a.) less than b.) equal to
Suppose the total mechanical energy of an object is conserved. Which one or more of the following statements is/are true? (a)If the kinetic energy decreases, the gravitational potential energy increases. (b)If the gravitational potential energy decreases, the kinetic energy increases. (c)If the kinetic energy does not change, the gravitational potential energy also does not change.
all are true ((a)If the kinetic energy decreases, the gravitational potential energy increases. (b)If the gravitational potential energy decreases, the kinetic energy increases. (c)If the kinetic energy does not change, the gravitational potential energy also does not change.)
Two objects with masses m1 and m2 are separated by a distance 2d. Mass m2 is greater than mass m1. A third object has a mass m3. All three objects are located on the same straight line. The net gravitational force acting on the third object is zero. Which one of the drawings correctly represents the locations of the objects?
answer: pic with m1------m3-------------m2
In which one or more of the following situations is the principle of conservation of mechanical energy obeyed? (a)An object moves uphill with an increasing speed. (b)An object moves uphill with a decreasing speed. (c)An object moves uphill with a constant speed. (d)An object moves downhill with an increasing speed. (e)An object moves downhill with a decreasing speed. (f)An object moves downhill with a constant speed.
b (An object moves uphill with a decreasing speed) d (An object moves downhill with an increasing speed)
In Example 10 the Kingda Ka roller coaster starts with a speed of 6.0m/s at the top of the drop and attains a speed of 50.3 m/s when it reaches the bottom. If the roller coaster were then to start up an identical hill, what speed would it attain when it reached the top? Assume that friction and air resistance are absent. (a)Greater than 6.0m/s (b)Exactly 6.0m/s (c)Between 0m/s and 6.0m/s (d)0m/s
b (Exactly 6.0m/s)
Two forces F1 and F2 are acting on the box shown in the drawing, causing the box to move across the floor. The two force vectors are drawn to scale. Which one of the following statements is correct? (a) F2 does more work than F1 does. (b) F1 does more work than F2 does. (c)Both forces do the same amount of work. (d)Neither force does any work.
b (F1 does more work than F2 does)
Consider the following situations: (i) A minivan is following a hairpin turn on a mountain road at a constant speed of twenty miles per hour. (ii) A parachutist is descending at a constant speed 10 m/s. (iii) A heavy crate has been given a quick shove and is now sliding across the floor. There is friction between the crate and floor. (iv) A child is swinging back and forth on a swing at the park. (v) A football that was kicked is flying through the goal posts. In which one of these situations does the object or person experience zero acceleration? a) i only b) ii only c) iii and iv only d) iv and v only e) all of the situations
b) ii only
In movies, Superman hovers in midair, grabs a villain by the neck, and throws him forward. Superman, however, remains stationary. This is not possible, because it violates which one or more of the following: (a)The law of conservation of energy (b)Newton's second law (c)Newton's third law (d)The principle of conservation of linear momentum
b, c, d
A net external force acts on a particle that is moving along a straight line. This net force is not zero. Which one of the following statements is correct? (a)The velocity, but not the kinetic energy, of the particle is changing. (b)The kinetic energy, but not the velocity, of the particle is changing. (c)Both the velocity and the kinetic energy of the particle are changing.
c (Both the velocity and the kinetic energy of the particle are changing)
A net force of 200 N acts on a 100-kg boulder, and a force of the same magnitude acts on a 130-g pebble. How does the rate of change of the boulder's momentum compare to the rate of change of the pebble's momentum? a) Greater than b) Less than c) Equal to d) Impossible to determine
c (Equal to)
In one case, a sports car, its engine running, is driven up a hill at a constant speed. In another case, a truck approaches a hill, and its driver turns off the engine at the bottom of the hill. The truck then coasts up the hill. Which vehicle is obeying the principle of conservation of mechanical energy? Ignore friction and air resistance. (a)Both the sports car and the truck (b)Only the sports car (c)Only the truck
c (Only the truck)
The bob swinging on a "stopped" pendulum will a) Not be able to swing to the same height from which it was released b) Swing to a height higher than from which it was released c) Swing to the same height from which it was released
c (Swing to the same height from which it was released)
Suppose that the coefficients of static and kinetic friction have values such that us = 1.4 uk for a crate in contact with a cement floor. Which one of the following statements is true? (a)The magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force. (b)The magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force. (c)The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.
c (The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force)
A uranium nucleus is at rest and undergoes a fission reaction, splitting into two fragments, one heavy and the other light. The magnitude of momentum is greater for which fragment? a) The heavy one b) The light one c) They both have the same momentum d) Impossible to determine
c (They both have the same momentum)
A circus performer hangs stationary from a rope. She then begins to climb upward by pulling herself up, hand over hand. When she starts climbing, is the tension in the rope (a)less than, (b)equal to, or (c)greater than it is when she hangs stationary?
c (greater than it is when she hangs stationary)
A ball has a speed of 15m/s. Only one external force acts on the ball. After this force acts, the speed of the ball is 7m/s. Has the force done (a)positive, (b)zero, or (c)negative work on the ball?
c (negative work on the ball)
A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is (a)stationary, (b)accelerating upward, and (c)accelerating downward. Rank the forces required in these three situations in ascending order—that is, smallest first.
c, a, b
Two cars are identical, except for the type of tread design on their tires. The cars are driven at the same speed and enter the same unbanked horizontal turn. Car A cannot negotiate the turn, but car B can. Which tread design, the one on car A or the one on car B, yields a larger coefficient of static friction between the tires and the road?
car B
On a frictionless surface, a sliding box collides and sticks to an identical box initially at rest. What is the final kinetic energy (KE) of the system in terms of the initial KE? a) KEf = KEi b) KEf = 1/4KEi c) KEf = 1/(root2) KEi d) KEf = 1/2Kei e)KEf= root(2KEi)
d (KEf = 1/2Kei)
A box is being moved with a velocity V by a force P (in the same direction as V) along a level horizontal floor. The normal force is Fn, the kinetic frictional force is fk, and the weight is mg. Which one of the following statements is correct? (a) P does positive work, Fn and fk do zero work, and mg does negative work. (b) Fn does positive work, P and fk do zero work, and mg does negative work. (c) fk does positive work, Fn and mg do zero work, and P does negative work. (d) P does positive work, Fn and mg do zero work, and fk does negative work.
d (P does positive work, Fn and mg do zero work, and fk does negative work)
During the final stages of descent, a sky diver with an open parachute approaches the ground with a constant velocity. There is no wind to blow him from side to side. Which one of the following statements is true? (a)The sky diver is not in equilibrium. (b)The force of gravity is the only force acting on the sky diver, so that he is in equilibrium. (c)The sky diver is in equilibrium because no forces are acting on him. (d)The sky diver is in equilibrium because two forces act on him, the downward-acting force of gravity and the upward-acting force of the parachute.
d (The sky diver is in equilibrium because two forces act on him, the downward-acting force of gravity and the upward-acting force of the parachute)
You are riding in the forward passenger seat of a car as it travels along a straight portion of highway. The car continues traveling at a constant speed as it follows a sharp, unbanked curve to the left. You feel the door pushing on the right side of your body. Which of the following forces in the horizontal direction are acting on you? a) a static frictional force between you and the seat b) a normal force of the door c) a force pushing you toward the door d) answers a and b e) answers a and c
d (answers a and b)
A pendulum bob of mass m is attached to the ceiling by a thin wire of length L. The bob moves at constant speed in a horizontal circle of radius R, with the wire making a constant angle β with the vertical. The tension in the wire A. is greater than mg. B. is equal to mg. C. is less than mg. D. could be two of the above, depending on the values of m, L, R, and β. E. could be all three of the above, depending on the values of m, L, R, and β.
A (is greater than mg)
A car is traveling at a constant speed along the road ABCDE shown in the drawing. Sections AB and DE are straight. Rank the accelerations in each of the four sections according to magnitude, listing the smallest first.
AB or DE, CD, BC
A nonzero net force acts on an object. Which of the following quantities could be constant? A. the object's kinetic energy B. the object's speed C. the object's velocity D. more than one of A, B, and C E. none of A, B, or C
D (more than one of A, B, and C)
Other things being equal, would it be easier to drive at high speed around an unbanked horizontal curve on the moon than to drive around the same curve on the earth?
No
A freight train is accelerating on a level track. Other things being equal, would the tension in the coupling between the engine and the first car change if some of the cargo in the last car were transferred to any one of the other cars?
No, because the transfer described does not change the total mass being pulled by the engine.
In an elastic collision, is the kinetic energy of each object the same before and after the collision?
No. It is the total kinetic energy of the system that is the same before and after the collision.
The speedometer of your car shows that you are traveling at a constant speed of 35 m/s. Is it possible that your car is accelerating?
Yes, if you are going around a curve.
Suppose you are standing on the edge of a dock and jump straight down. If you land on sand your stopping time is much shorter than if you land on water. Using the impulse-momentum theorem as a guide, determine which one of the following statements is correct. (a)In bringing you to a halt, the sand exerts a greater impulse on you than does the water. (b)In bringing you to a halt, the sand and the water exert the same impulse on you, but the sand exerts a greater average force. (c)In bringing you to a halt, the sand and the water exert the same impulse on you, but the sand exerts a smaller average force.
b (In bringing you to a halt, the sand and the water exert the same impulse on you, but the sand exerts a greater average force)
Is it correct to conclude that one engine is doing twice the work that another is doing just because it is generating twice the power? (a)Yes (b)No
b (No)
Which ball is more likely to knock the block over? a) The ball that thuds against the block b) The ball that bounces off the block c) Both have the same chance of knocking over the block since their masses are the same
b (The ball that bounces off the block)
When a body is moved from sea level to the top of a mountain, what changes: (a)the body's mass, (b)its weight, (c)both its mass and its weight?
b (its weight)
A stone is thrown from the top of a cliff. Air resistance is negligible. As the stone falls, is it (a)in equilibrium or (b)not in equilibrium?
b (not in equilibrium)
A force does positive work on a particle that has a displacement pointing in the +x direction. This same force does negative work on a particle that has a displacement pointing in the +y direction. In which quadrant of the x, y coordinate system does the force lie? (a)First (b)Second (c)Third (d)Fourth
d (Fourth)
Consider the recoil of a rifle when it is fired. Recoil is an example of which of the following concepts? a) Newton's Third Law of Motion b) Impulse c) Conservation of Momentum d) all of the above e) none of the above
d (all of the above)
An ice boat is coasting on a frozen lake. Friction between the ice and the boat is negligible, and so is air resistance. Nothing is propelling the boat. From a bridge someone jumps straight down into the boat, which continues to coast straight ahead. (b) Does the speed of the boat itself increase, decrease, or remain the same?
decrease
You are a passenger on a jetliner that is flying at a constant velocity. You get up from your seat and walk toward the front of the plane. Because of this action, your forward momentum increases. Does the forward momentum of the plane itself decrease, remain the same, or increase?
decrease
A net external nonconservative force does positive work on a particle. Based solely on this information, you are justified in reaching only one of the following conclusions. Which one is it? (a)The kinetic and potential energies of the particle both decrease. (b)The kinetic and potential energies of the particle both increase. (c)Neither the kinetic nor the potential energy of the particle changes. (d)The total mechanical energy of the particle decreases. (e)The total mechanical energy of the particle increases.
e (The total mechanical energy of the particle increases)
The Moon does not crash into Earth because a) it's in Earth's gravitational field. b) the net force on it is zero. c) it is beyond the main pull of Earth's gravity. d) it's being pulled by the Sun as well as by Earth. e) none of the above
e (none of the above; The Moon does not crash into Earth because of its high speed tangential to its path. If it slowed down or stopped moving all together, it would, of course, fall directly into Earth. With its high speed, the Moon would fly off into space if it weren't for gravity providing the centripetal force.)
A penny is placed on a rotating turntable. Where on the turntable does the penny require the largest centripetal force to remain in place: at the center of the turntable or at the edge of the turntable?
edge of the turntable
A satellite explodes in outer space, far from any other body, sending thousands of pieces in all directions. Is the linear momentum of the satellite before the explosion less than, equal to, or greater than the total linear momentum of all the pieces after the explosion?
equal to
A stone is tied to a string and whirled around in a circle at a constant speed. Is the string more likely to break when the circle is horizontal or when it is vertical? Assume that the constant speed is the same in each case.
vertical
On a distant asteroid, a large catapult is used to throw chunks of stone into space. Could such a device be used as a propulsion system to move the asteroid closer to the earth?
yes
