Physics 210 Final
Three cars, A, B, and C, are moving along a straight section of a highway. If the velocity of A relative to B is +60 m/s and the velocity of A relative to C is +20 m/s, then what is the velocity of C relative to B? +40 m/s -80 m/s -40 m/s +80 m/s
+40m/s
A honeybee leaves the hive and travels a total distance of 2 km before returning to the hive. What is the magnitude of the displacement vector of the bee?
0 km
The blade of a lawn mower is rotating at an angular speed of 128 rad/s. The tangential speed of the outer edge of the blade is 32 m/s. What is the radius of the blade? 0.25 m 0.50 m 1.0 m 4.0 m
0.25m
he blades of a ceiling fan start from rest and, after two revolutions, have an angular speed of 0.5 rev/s. The angular acceleration of the blades is constant. What is the angular speed after eight revolutions? 0.50 rev/s 1.0 rev/s 2.0 rev/s 4.0 rev/s
1.0 rev/s
A straight track is 1600 m in length. A runner begins at the starting line, runs due east for the full length of the track, turns around and runs halfway back. The time for this run is five minutes. What is the magnitude of the runner's average velocity?
160 meters per minute
A straight track is 1600 m in length. A runner begins at the starting line, runs due east for the full length of the track, turns around and runs halfway back. The time for this run is five minutes. What is the runner's average speed?
480 meters per minute
A power boat, starting from rest, maintains a constant acceleration. After a certain time t, its displacement and velocity are r and v. At time 2t, what would be its displacement and velocity, assuming the acceleration remains the same? 4 r and 4 v 2 r and 2 v 2 r and 4 v 4 r and 2 v
4r and 2v b/c when time doubles, distance is 1/2a(t)^2
A rotating object starts from rest and has a constant angular acceleration. Three seconds later the centripetal acceleration of a point on the object has a magnitude of 2.0 m/s2. What is the magnitude of the centripetal acceleration of this point six seconds after the motion begins? 2.0 m/s2 4.0 m/s2 8.0 m/s2
8.0 m/s^2
t is possible to build a clock in which the tips of the hour hand and the second hand move with the same tangential speed. This is normally never done, however. Why? A- The length of the hour hand would be 720 times greater than the length of the second hand. B- The hour hand and the second hand would have the same length. C- The length of the hour hand would be 720 times smaller than the length of the second hand.
A
Two boxes have masses m1 and m2, and m2 is greater than m1. The boxes are being pushed across a frictionless horizontal surface. As the drawing shows, there are two possible arrangements, and the pushing force is the same in each. In which arrangement does the force that the left box applies to the right box have a greater magnitude, or is the magnitude the same in both cases? A- Arrangement (a), m1 on the left B- Arrangement (b), m2 on the left A-The magnitude is the same in both cases
A Consider that in both cases the same force is pushing on the same total mass, so the accelerations will be equal in both cases. In arrangement (a) it is the larger mass, m2, which is being accelerated by the force exerted by the left box, so that force must have a greater magnitude (compared to arrangement (b)) in order to achieve the same acceleration.
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. What is true about the radius of the orbit of the satellite that orbits Mars? A- It is less than the radius of the orbit of the satellite orbiting Jupiter. B- It is greater than the radius of the orbit of the satellite orbiting Jupiter. C- It is equal to the radius of the orbit of the satellite orbiting Jupiter.
A This is because the mass of Mars is less than that of Jupiter.
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 above could the object possibly be in equilibrium.
A In this situation equilibrium will occur if the three forces cancel: the magnitudes of the two forces in one direction add together and equal the magnitude of the single force in the opposite direction.
A father and his seven-year-old daughter (who have different masses) are facing each other on ice skates. With their hands, they push off against one another. Which one or more of the following statements is (are) true? a-Each experiences an acceleration that has a different magnitude. b-Each experiences an acceleration of the same magnitude. c-Each experiences a pushing force that has a different magnitude. d- Each experiences a pushing force that has the same magnitude.
A and d Consider what Newton's third law says about the pushing forces that they exert on each other. Then consider what Newton's second law says about their accelerations since their masses are different.
Suppose that the coefficients of static and kinetic friction have values such that μs = 1.4 μk for a crate in contact with a cement floor. Which one of the following statements is true? A-The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force. B-The magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force. C- The magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force.
A b/c fsMAX = μsFN and fk = μkFN, so since μs = 1.4 μk and FN is the same in both cases, therefore fsMAX = 1.4 fk and the statement is true.
In Case A an object is moving straight downward with a constant speed of 9.80 m/s, while in Case B an object is moving straight downward with a constant acceleration of magnitude 9.80 m/s2. Which one of the following is true? A nonzero net external force acts on the object in both cases. A nonzero net external force acts on the object in neither case. A nonzero net external force acts on the object in Case A only. A nonzero net external force acts on the object in Case B only.
A nonzero net external force acts on the object in Case B only. a nonzero net external force will cause an acceleration.
A car is up on a hydraulic lift at a garage. The wheels are free to rotate, and the drive wheels are rotating with a constant angular velocity. Which one of the following statements is true? A point on the rim has no tangential and no centripetal acceleration. A point on the rim has both a nonzero tangential acceleration and a nonzero centripetal acceleration. A point on the rim has a nonzero tangential acceleration but no centripetal acceleration. A point on the rim has no tangential acceleration but does have a nonzero centripetal acceleration.
A point on the rim has no tangential acceleration but does have a nonzero centripetal acceleration.
Which of these would be affected by a change in the earth's mass? the banking of roadbeds the speeds with which satellites are put into circular orbits the performance of the loop-the-loop motorcycle stunt the banking of airplanes as they turn
All four
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 three
A thin sheet of plastic is uniform and has the shape of an equilateral triangle. Consider two axes for rotation. Both are perpendicular to the plane of the triangle, axis A passing through the center of the triangle and axis B passing through one corner. If the angular speed ω about each axis is the same, for which axis does the triangle have the greater rotational kinetic energy? A B
B
Equation 8.7 (theta equals omega Subscript 0 Baseline t plus StartFraction 1 Over 2 EndFraction alpha t Superscript 2) is being used to solve a problem in rotational kinematics. Which one of the following sets of values for the variables ω0, α, and t cannot be substituted directly into this equation to calculate a value for θ? A- ω0 = 1.0 rad/s, α = 1.8 rad/s2, and t = 3.8 s. B- ω0 = 0.16 rev/s, α = 1.8 rad/s2, and t = 3.8 s. C- ω0 = 0.16 rev/s, α = 0.29 rev/s2, and t = 3.8 s.
B
The drawing shows an overhead view of a horizontal bar that is free to rotate about an axis perpendicular to the page. Two forces act on the bar, and they have the same magnitude. However, one force is perpendicular to the bar, and the other makes an angle φ with respect to it. The angle can be 90˚, 45˚, or 0˚. Rank the values of φ according to the magnitude of the net torque (the sum of the torques) that the two forces produce, largest net torque first. A- 90˚, 45˚, 0˚ B- 0˚, 45˚, 90˚ C- 45˚, 0˚, 90˚
B
A stone is thrown from the top of a cliff. Air resistance is negligible. As the stone falls, is it in equilibrium or not in equilibrium? A- in equilibrium B- not in equilibrium
B Since air resistance is negligible the stone will accelerate due to the force of gravity pulling it downward. Since it is accelerating, it is not in equilibrium.
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 and D
Concept Simulation 7.1 reviews the concepts that are pertinent in this question. 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
Three objects are visible in the night sky. They have the following diameters (in multiples of d) and subtend the following angles (in the multiples of θ0) at the eye of the observer. Object A has a diameter of 4d and subtends an angle of 2θ0. Object B has a diameter of 3d and subtends an angle of θ0/2. Object C has a diameter of d/2 and subtends an angle of θ0/8. Rank them in descending order (greatest first) according to their distance from the observer. A, B, C B, A, C C, A, B B, C, A
B, C, A
Two balls are launched upward from the same spot at different angles with respect to the ground. Both balls rise to the same maximum height. Ball A, however, follows a trajectory that has a greater range that that of ball B. Ignoring air resistance, decide which ball, if either, has the greater launch speed. Ball A. Ball B. The speeds are the same.
Ball A
Bob and Bill have the same weight and wear identical shoes. When they both keep their feet flat on the floor and their bodies straight, Bob can lean forward farther than Bill can before falling. Other things being equal, whose center of gravity is closer to the ground when both are standing er Bill Bob
Bob
Which of the following statements can be explained by Newton's first law? (A) When your car suddenly comes to a halt, you lunge forward. (B) When your car rapidly accelerates, you are pressed backward against the seat. Neither A nor B Both A and B A but not B B but not A
Both A and B Statement A illustrates Newton's first law because your body is initially moving forward, and when the car stops it continues forward. Statement B illustrates Newton's first law because your body tends to remain in its initial state (either rest or moving forward at some speed), so when the car accelerates forward, your body remains behind, pressing you backward in your seat.
Which of the following statements about centripetal acceleration is true? More than one statement or no statements may be true. An object moving at a constant speed may have a centripetal acceleration. An object moving at a constant velocity cannot have a centripetal acceleration.
Both are true
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? The velocity, but not the kinetic energy, of the particle is changing. The kinetic energy, but not the velocity, of the particle is changing. Both the velocity and the kinetic energy of the particle are changing.
Both the velocity and the kinetic energy of the particle are changing
Two objects have the same momentum. How do their velocities compare? A- They must have same directions and the same magnitudes. B- They must have the same magnitudes but they could have different directions. C- They must have the same directions but they could have different magnitudes. D- Their directions and the magnitudes could both be different.
C
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 A car B
Car b b/c If the car has enough static friction, then it can make the turn safely.
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 Equilibrium occurs when these two forces have equal magnitudes.
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? Downward when it reads 75 N and upward when it reads 120 N Upward when it reads 75 N and downward when it reads 120 N Downward in both cases Upward in both cases
Downward when it reads 75N and upwards when it reads 120N b/c the true weight of the suitcase is (10 kg)*(9.8 m/s2) = 98 N. When the scale reads 75 N the acceleration must be downward, partially counteracting the pull of gravity. When the scale reads 120 N the acceleration must be upward, adding to the pull of gravity.
A leopard springs upward at a 45 degree angle and then falls back to the ground. Air resistance is negligible. There exists a point on the leopard's trajectory at which its speed is one-half its initial value. True False
False
A person is hanging motionless from a vertical rope over a swimming pool. She lets go of the rope and drops straight down. After letting go, it is possible for her to curl into a ball and start spinning. True False
False
A plane takes off at St. Louis, flies straight to Denver, and then returns the same way. The plane flies at the same speed with respect to the ground during the entire flight, and there are no head winds or tail winds. Since the earth revolves around its axis once a day, you might expect that the times for the outbound trip and the return trip differ, depending on whether the plane flies against the earth's rotation or with it. Is this expectation true or false? True False
False
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. True False
False
In an elastic collision, the kinetic energy of each object is always the same before and after the collision. True False
False
On a riverboat cruise, a plastic bottle is accidentally dropped overboard. A passenger on the boat estimates that the boat pulls ahead of the bottle by 5 meters each second. It is possible to conclude that the magnitude of the velocity of the boat with respect to the shore is 5 m/s. True False
False
Two buses depart from Chicago, one going to New York and one to San Francisco. Each bus travels at a speed of 30 m/s, so they have equal velocities. True False
False
The acceleration of a projectile is equal to zero when the projectile reaches the top of its trajectory. True False
False b/c for projectile motion, the acceleration is due to gravity.
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? First Second Third Fourth
Fourth
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 less than, equal to, or greater than it is when she hangs stationary? less than equal to greater than
Greater than When the performer is climbing up she is accelerating upward, which is the result of increased tension in the rope.
Two cars are moving in the same direction (the positive direction) on a straight road. The acceleration of each car also points in the positive direction. Car 1 has a greater acceleration than car 2 has. Which one of the following statements is true? The velocity of car 1 is always greater than the velocity of car 2. The velocity of car 2 is always greater than the velocity of car 1. In the same time interval, the velocity of car 1 changes by a greater amount than car 2 does. In the same time interval, the velocity of car 2 changes by a greater amount than the velocity of car 1 does.
In the same time interval, the velocity of car 1 changes by a greater amount than car 2 does.
A runner runs half the remaining distance to the finish line every ten seconds. She runs in a straight line and does not ever reverse her direction. Does her acceleration have a constant magnitude? Yes No
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? A- Yes B- No C- Possibly, depending on to which car the mass was transferred.
No
A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? Yes. No.
No
An object moving with a constant acceleration slows down if the acceleration points in the direction opposite to the direction of the velocity. But can an object ever come to a permanent halt if its acceleration truly remains constant? Yes No
No
At one instant of time, a car and a truck are traveling side by side in adjacent lanes of a highway. The car has a greater velocity than the truck has. Does the car necessarily have the greater acceleration? Yes No
No
Two identical automobiles have the same speed, one traveling east and one traveling west. Do these cars have the same momentum? Yes No
No
Newton's second law indicates that when a net force acts on an object, it must accelerate. Does this mean that when two or more forces are applied to an object simultaneously, it must accelerate? Yes No
No Since forces are vectors, two or more forces could add in such a way that they cancel and result in a zero net force, so there will be no acceleration.
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? Yes No
No The downward force of gravity on the crate will cause it to accelerate downward unless it is opposed by an upward force, which must result from the upward component of the tension force. If the rope were perfectly horizontal, then the upward component of the tension would be zero.
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? Yes. No.
No b/c power is the rate at which work is done
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 θ is the same in both cases, does it require less force to push or to pull the sled? Push Pull The magnitude of the force is the same for both pushing and pulling.
Pull In the diagram showing pushing, there is a component of the pushing force which is downward, and so the normal force between the sled and the ground will be greater than the weight of the sled. In the diagram showing pulling, there is a component of the pushing force which is upward, and so the normal force between the sled and the ground will be less than the weight of the sled. Since the pulling case has the smaller normal force it will have the smaller kinetic friction force, and therefore it takes less force to pull the sled.
Three swimmers can swim equally fast relative to the water. They have a race to see who can swim across a river in the least time. Swimmer A swims perpendicular to the current and lands on the far shore downstream, because the current has swept him in that direction. Swimmer B swims upstream at an angle to the current and lands on the far shore directly opposite the starting point. Swimmer C swims downstream at an angle to the current in an attempt to take advantage of the current. Who crosses the river in the least time? Note: The width of the river and the velocity of the water with respect to the ground are both constant. Swimmer A Swimmer B Swimmer C
Swimmer A
Suppose you are driving due east, traveling a distance of 1500 m in 2 minutes. You then turn due north and travel the same distance in the same time. What can be said about the average speeds and the average velocities for the two segments of the trip? The average speeds and the average velocities are the same. The average speeds are the same, but the average velocities are different. The average speeds are different, but the average velocities are the same.
The average speeds are the same, but the average velocities are different.
A tennis ball is hit upward into the air and moves along an arc. Neglecting air resistance, where along the arc do the minimum and maximum speeds occur? The ball's speed is constant so the minimum and maximum speed occurs at every point. The minimum speed occurs at the lowest point and the maximum occurs at the highest. The maximum speed occurs at the lowest point and the minimum occurs at the highest.
The maximum speed occurs at the lowest point and the minimum occurs at the highest.
The net external force acting on an object is zero. Which one of the following statements is true? The object can only be stationary. The object can only be traveling with a constant velocity. The object can be either stationary or traveling with a constant velocity. The object can only be traveling with a velocity that is changing.
The object can be either stationary or traveling with a constant velocity. Newton's first law states that if the net force on an object is zero, it will either move with constant velocity or remain at rest (which is a special case of constant velocity).
A child is playing on the floor of a recreational vehicle (RV) as it moves along the highway at a constant velocity. He has a toy cannon, which shoots a marble at a fixed angle and speed with respect to the floor. The cannon can be aimed toward the front or rear of the RV. How do the marble's ranges compare from the child's point of view and from the point of view of an observer standing still on the ground? The two ranges are equal from both points of view. The two ranges are equal from the child's point of view only. The two ranges are equal from the point of view of the observer on the ground only.
The two ranges are equal from the child's point of view only.
An object is thrown upward at an angle Ө above the ground, eventually returning to earth. Which statement is true? The velocity and acceleration are always perpendicular. The velocity and acceleration are always parallel. The velocity and acceleration are parallel only at the top of the trajectory. The velocity and acceleration are perpendicular only at the top of the trajectory.
The velocity and acceleration are perpendicular only at the top of the trajectory.
Other things being equal, which would be easier? To drive at high speed around an unbanked horizontal curve on the moon. To drive at high speed around an unbanked horizontal curve on the earth. Neither would be easier because there's no difference.
To drive at high speed around an unbanked horizontal curve on the earth.
A wrench is accidentally dropped from the top of the mast on a sailboat. Air resistance is negligible. The wrench will hit at the same place on the deck whether the sailboat is at rest or moving with a constant velocity. True False
True
The average velocity for a trip has a positive value. It is possible for the instantaneous velocity at a point during the trip to have a negative value. True False
True
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 No It depends on the circumstances.
Yes
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 No
Yes
https://edugen.wileyplus.com/edugen/shared/lws/main.uni?assignment=asnmt1463439&agtype=3&classid=cls599093&mode=practice&scheme=student&context=book
a and c
Rolling motion is an example that involves rotation about an axis that is not fixed. Which one of the following is another example of rotational motion about an axis that is not fixed? a stunt plane flies around a circular course a passenger rides on a Ferris Wheel a spinning basketball goes through the hoop a sample of blood spins in a centrifuge
a spinning basketball goes through the hoop
An experimental vehicle slows down and comes to a halt with an acceleration whose magnitude is 9.80 m/s2. After reversing direction in a negligible amount of time, the vehicle speeds up with an acceleration of 9.80 m/s2. Except for being horizontal, is this motion (a) the same as or (b) different from the motion of a ball that is thrown straight upward, comes to a halt, and falls back to earth? Ignore air resistance. a- same b- different
a- same
Water, dripping at a constant rate from a faucet, falls to the ground. At any instant there are many drops in the air between the faucet and the ground. Where does the center of mass of the drops lie relative to the halfway point between the faucet and the ground? Above it Below it Exactly at the halfway point
above it
A woman is sitting on a spinning seat of a piano stool with her arms folded. Ignore any friction in the spinning stool. What happens to her angular velocity and angular momentum when she extends her arms outward? angular velocity changes and angular momentum changes angular velocity changes and angular momentum remains the same both remain the same
angular velocity changes and angular momentum remains the same
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 at the edge of the turntable
at the edge of the turntable
You are standing on a scale in an elevator that is moving upward with a constant velocity. The scale reads 600 N. Below are five options for what the scale reads when the elevator slows down as it comes to a stop, when it is stopped, and when it picks up speed on its way back down. Which one of the five options correctly describes the scale's readings? Note that the symbol < means "less than" and > means "greater than." Elevator slows to Elevator stopped Elevator inc. stop upwards going down a - >600N >600N >600N b- <600N 600N <600N c- >600N 600N <600N
b Since the elevator is initially moving at constant velocity there is no net force on you, so the scale reading of 600 N is your true weight. When the elevator is at rest it will read your true weight of 600 N, and in the other two cases it is accelerating downward and so the scale will read ‹ 600 N.
In baseball, the pitcher's mound is raised to compensate for the fact that the ball falls downward as it travels from the pitcher toward the batter. If baseball were played on the moon, where would the pitcher's mound have to be? Entry field with correct answer (a) higher than its height on earth. (b) lower than its height on earth. (c) the same as its height on earth.
b) lower than its height on earth b/c the ball will fall less distance due to the lesser acceleration due to gravity on the moon
A ball is dropped from rest from the top of a building and strikes the ground with a speed vf. From ground level, a second ball is thrown straight upward at the same instant that the first ball is dropped. The initial speed of the second ball is v0 = vf, the same speed with which the first ball eventually strikes the ground. Ignoring air resistance, decide whether the balls cross paths (a) at half the height of the building, (b) above the halfway point, or (c) below the halfway point. (a) (b) (c)
b- above the halfway point
Two objects are thrown vertically upward, first one, and then, a bit later, the other. Is it (a) possible or (b) impossible that both objects reach the same maximum height at the same instant of time? (a) possible (b) impossible
b- impossible
A rifle, at a height H above the ground, fires a bullet parallel to the ground. At the same instant and at the same height, a second bullet is dropped from rest. In the absence of air resistance, which bullet, if either, strikes the ground first? The first bullet The second bullet Both bullets.
both bullets
All of the following, except one, cause the acceleration of an object to double. Which one is the exception? The net force acting on the object remains the same, while the mass of the object is reduced by a factor of two. Both the net force acting on the object and the mass of the object double. All forces acting on the object double. The net force acting on the object doubles.
both the net force acting on the object and the mass of the object double Since according to Newton's second law acceleration is net force divided by mass, if both the net force and the mass double, the acceleration will remain the same.
Concept Simulation 7.2 illustrates the concepts that are involved in this question. Also review Multiple-Concept Example 7. 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 intial speed, while object 2 moves to the right, as in Figure 7.11, 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
A canoe with two people aboard is coasting with an initial momentum of +110 kg m/s. Then, one of the people (person 1) dives off the back of the canoe. During this time, the net average external force acting on the system (the canoe and the two people) is zero. The table lists four possibilities for the final momentum of person 1 and the final momentum of person 2 plus the canoe, immediately after person 1 dives off. Only one possibility could be correct. Which one is it? Person 1 Person 2 and Canoe (a) -60 kg·m/s +170 kg·m/s (b) -30 kg·m/s +110 kg·m/s (c) -40 kg·m/s -70 kg·m/s (d) +80 kg·m/s -30 kg·m/s
(a)
An airplane is flying horizontally with a constant momentum during a time interval Δt. (a) Is there a net impulse acting on the plane during this time? Use the impulse-momentum theorem to guide your thinking. (b) 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? (a) Yes. (b) They're equal in both magnitude and direction. (a) Yes. (b) They're equal in magnitude and opposite in direction. (a) No. (b) They're equal in both magnitude and direction. (a) No. (b) They're equal in magnitude and opposite in direction.
(a) No. (b) They're equal in magnitude and opposite in direction
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) less than (a) less than ; (b) equal to (a) greater than ; (b) greater than
(a) less than; (b) equal to
Two uniform solid balls are placed side by side at the top of an incline plane and, starting from rest, are allowed to roll down the incline. Which ball, if either, has the greater translational speed at the bottom if (a) they have the same radii, but one is more massive than the other; and (b) they have the same mass, but one has a larger radius? (a) the ball with the greater mass (b) the ball with the larger radius (a) the ball with the smaller mass (b) the ball with the smaller radius (a) the ball with the greater mass (b) the ball with the smaller radius (a) the ball with the smaller mass (b) the ball with the larger radius (a) neither (b) neither
(a) neither (b) neither
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? (b) Does the speed of the boat itself increase, decrease, or remain the same? (a) yes (b) increase (a) no (b) increase (a) yes (b) decrease (a) no (b) decrease (a) yes (b) remain the same (a) no (b) remain the same
(a) no (b) decrease
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? (b) Can the frictional force change the total linear momentum of the two-body system? (a) yes (b) yes (a) yes (b) no (a) no (b) yes (a) no (b) no
(a) no; (b) no
a) Can a single object have a kinetic energy and 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? (a) yes; (b) yes (a) yes; (b) no (a) no; (b) yes (a) no; (b) no
(a) no; (b) yes
The space probe in the drawing is initially moving with a constant translational velocity and zero angular velocity. (a) When the two engines are fired, each generating a thrust of magnitude T, does the translational velocity increase, decrease, or remain the same? (b) Does the angular velocity increase, decrease, or remain the same? (a) remain the same (b) remain the same (a) remain the same (b) increase (a) remain the same (b) decrease (a) increase (b) remain the same (a) decrease (b) remain the same
(a) remain the same (b) increase
At a given instant an object has an angular velocity. It also has an angular acceleration due to torques that are present. Therefore, the angular velocity is changing. Does the angular velocity at this instant increase, decrease, or remain the same (a) if additional torques are applied so as to make the net torque suddenly equal to zero and (b) if all the torques are suddenly removed? (a) remain the same (b) remain the same (a) remain the same (b) increase (a) remain the same (b) decrease (a) increase (b) remain the same (a) decrease (b) remain the same
(a) remain the same (b) remain the same
Is it possible (a) for a large force to produce a small, or even zero, torque and (b) for a small force to produce a large torque? (a) yes (b) yes (a) yes (b) no (a) no (b) yes (a) no (b) no
(a) yes (b) yes
A sunbather is lying on a floating raft that is staionary. She then gets up and walks to one end of the raft. Consider the sunbather and raft as an isolated system. (a) What is the velocity of the center of mass of this system while she is walking? (b) Does the raft itself move while she is walking? If so, what is the direction of the raft's velocity relative to that of the sunbather? (a) zero (b) The raft doesn't move relative to the sunbather. (a) her velocity with respect to the water (b) The raft doesn't move relative to the sunbather. (a) zero (b) The raft moves toward the other end relative to the sunbather. (a) her velocity with respect to the water (b) The raft moves toward the other end relative to the sunbather.
(a) zero (b) the raft moves toward the other end relative to the sunbather
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)
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. b < a < c a < c < b a < b < c b < c < a c < a < b c < b < a
c < a < b The force required to start the box sliding is equal to the magnitude of the maximum static friction force, which is proportional to the normal force between the box and the elevator floor. When the elevator is stationary this normal force is equal to the true weight of the box, when the elevator is accelerating upward this normal force is greater than the true weight, and when the elevator is accelerating downward this normal force is less than the true weight.
A thin rod rotates at a constant angular speed. In case A the axis of rotation is perpendicular to the rod at its center. In case B the axis is perpendicular to the rod at one end. In which case, if either, are there points on the rod that have the same tangential speeds? case A case B both
case A
A bicycle is turned upside down, the front wheel is spinning (see the drawing), and there is an angular acceleration. At the instant shown, there are six points on the wheel that have arrows associated with them. Which one of the following quantities could the arrows not represent? Tangential velocity Centripetal acceleration Tangential acceleration
centripetal acceleration
Review Conceptual Exercise 14 as an aid in answering this question. Suppose the ice cap at the South Pole melted and the water was distributed uniformly over the earth's oceans. Would the earth's angular velocity increase, decrease, or remain the same? increase decrease 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 remain the same increase
decrease
A stone is thrown horizontally from the top of a cliff and eventually hits the ground below. A second stone is dropped from rest from the same cliff, falls through the same height, and also hits the ground below. Ignore air resistance. Which of the following quantities is or are different for the two cases? (More than one quantity may be different.) Displacement Speed just before impact with the ground Time of flight
displacement and speed just before impact with the ground
The drawing shows an empty fuel tank about to be released by three different jet planes. At the moment of release, each plane has the same speed, and each tank is at the same height above the ground. However, the directions of the velocities of the planes are different. Which tank has the largest speed upon hitting the ground? Ignore friction and air resistance. A B C Each tank hits the ground with the same speed.
each tank hits the ground with the same speed
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? Engines A and B can do the same amount of work, but engine A can do it more quickly. Engines A and B can do the same amount of work in the same amount of time. In the same amount of time, engine B can do more work than engine A.
engines A and B can do the same amount of work, but engine A can do it more quickly
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? less than equal to greater than
equal to
In Example 10 the Kingda Ka roller coaster starts with a speed of 6.0 m/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 to then start up an identical hill, what speed would it attain when it reached the top? Assume that friction and air resistance are absent. Greater than 6.0 m/s Exactly 6.0 m/s Between 0 m/s and 6.0 m/s 0 m/s
exactly 6.0 m/s
A pair of scissors is being used to cut a piece of paper in half. Each blade of the scissors has the same angular velocity (both magnitude and direction) at a given instant. True False
false
Conceptual Example 14 provides background for this question. A cloud of interstellar gas is rotating. Because the gravitational force pulls the gas particles together, the cloud shrinks, and, under the right conditions, a star may ultimately be formed. Would the angular velocity of the star be less than, equal to, or greater than the angular velocity of the rotating gas? less than greater than equal to
greater than
Sometimes, even with a wrench, one cannot loosen a nut that is frozen tightly to a bolt. It is often possible to loosen the nut by slipping one end of a long pipe over the wrench handle and pushing at the other end of the pipe. With the aide of the pipe, does the applied force produce a smaller torque, a greater torque, or the same torque on the nut? smaller torque greater torque same torque
greater torque
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 describes how the gravitational potential energy of the astronaut changes during the climb? It changes by a greater amount on the earth. It changes by a greater amount on the moon. The change is the same in both cases.
it changes by a greater amount on the earth
Starting in the spring, fruit begins to grow on the outer end of a branch on a pear tree. As the fruit grows, which of the following is true for the center of gravity of the pear-growing branch? It moves toward the pears at the end of the branch. It moves away from the pears. It does not move at all.
it moves toward the pears at the end of the branch
Section 5.6 discusses how the uniform circular motion of a space station can be used to create artificial gravity. This can be done by adjusting the angular speed of the space station, so the centripetal acceleration at an astronaut's feet equals g, the magnitude of the acceleration due to the earth's gravity. If such an adjustment is made, what will be true about the acceleration at the astronaut's head due to the artificial gravity? It will be greater than g. It will be equal to g. It will be less than g.
it will be less than g
The speedometer of a truck is set to read the linear speed of the truck, but uses a device that actually meausures the angular speed of the rolling tires that came with the truck. However, the owner replaces the tires with larger-diameter versions. Does the reading on the speedometer after the replacement give a speed that is less than, equal to, or greater than the true linear speed of the truck? less than equal to greater than
less than
here would you expect the center of mass of a baseball bat to be located? halfway between the ends of the bat nearer the lighter end nearer the heavier end
nearer the heavier end
A ball has a speed of 15 m/s. Only one external force acts on the ball. After this force acts, the speed of the ball is 7 m/s. Has the force done positive, zero, or negative work on the ball? positive zero negative
negative
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? Yes, you can distinguish between the three situations. No, such a determination cannot be made.
no, such a determination cannot be made b/c in all three cases the stack of books is moving with constant velocity, and so all you can tell is that the net force is zero in each case.
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? On three of the four corners of a square On the corners of an equilateral triangle On the corners of a right triangle
on the corners of an equilateral triangle b/c in an equilateral triangle there is complete symmetry to the forces, so the magnitudes of the net forces will be equal.
The earth rotates once per day about its axis, which is perpendicular to the plane of the equator and passes through the north geographic pole. Where on the earth's surface should you stand in order to have the smallest possible tangential speed? on the north geographic pole or on the south geographic pole on the equator
on the north geographic pole or on the south geographic pole
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. Both the sports car and the truck Only the sports car Only the truck
only the truck
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 positive when you ride up and negative when you ride down. negative when you ride up and positive when you ride down. positive when you ride up or down. negative when you ride up or down.
positive when you ride up and negative when you ride down.
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? It's possible. It is not possible.
possible
Is the average speed of a vehicle a vector or a scalar quantity?
scaler
A hoop, a solid cylinder, a spherical shell, and a solid sphere are placed at rest at the top of an incline. All the objects have the same radius. They are then released at the same time. What is the order in which they reach the bottom (fastest first)? solid sphere, cylinder, shell, hoop cylinder, shell, solid sphere, hoop hoop, cylinder, shell, solid sphere shell, hoop, cylinder, solid sphere
solid sphere, cylinder, shell, hoop
A motorcycle starts from rest and has a constant acceleration. In a time interval t, it undergoes a displacement x and attains a final velocity v. Then t is increased so that the displacement is 3x. In this same increased time interval, what final velocity does the motorcycle attain? 9v 3v v square root of 3 v
square root of 3v
One of the following statements is incorrect. (a) The car traveled around the circular track at a constant velocity. (b) The car traveled around the circular track at a constant speed. Which statement is incorrect? Statement a Statement b
statement a
When a body is moved from sea level to the top of a mountain, what changes? the body's mass the body's weight both the body's mass and weight
the body's weight b/c the mass of an object is the same everywhere in the universe but its weight depends on the local value of gravity, which will be smaller at the top of a mountain than at sea level.
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 recoiled cannon? Assume that momentum conservation applies. the cannonball the cannon
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 north pole. The person at the equator.
the person at the equator
The muzzle velocity of a gun is the velocity of the bullet when it leaves the barrel. The muzzle velocity of one rifle with a short barrel is greater than the muzzle velocity of another rifle that has a longer barrel. In which rifle is the acceleration of the bullet larger? The rifle with the long barrel. The rifle with the short barrel.
the rifle with the short barrel
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? The rope tied to the tree The rope in the tug-of-war Both ropes sustain the same tension.
the rope tied to the tree Consider that there would be no difference, as far as tension in the rope is concerned, between five people pulling against a rope tied to a tree and five people pulling against five other people. In both cases, the five people are pulling against an immovable opponent. Then realize that in the case here, it is ten people pulling against the tree, not five, so the tension is greater.
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? Assume that both cars have the same speed and are equipped with identical tires. worse the same better
the same b/c mass doesn't affect the maximum safe speed
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? The kinetic and potential energies of the particle both decrease. The kinetic and potential energies of the particle both increase. Neither the kinetic nor the potential energy of the particle changes. The total mechanical energy of the particle decreases. The total mechanical energy of the particle increases.
the total mechanical energy of the particle increases
A building is located on the earth's equator. As the earth rotates about its axis, which floor of the building has the greatest tangential speed? the first floor the tenth floor the twentieth floor
the twentieth floor
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. horizontal vertical
vertical b/c the force due to gravity is an additional force which will make it more likely to break in this orientation.
An electric clock is hanging on a wall. As you are watching the second hand rotate, the clock's battery stops functioning, and the second hand comes to a halt over a brief period of time. Which one of the following statements correctly describes the angular velocity ω and angular acceleration α of the second hand as it slows down? ω and α are both negative. ω is positive and α is negative. ω is negative and and α is positive. ω and α are both positive.
w is negative and and a is positive
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? zero their average speed multiplied by their total mass their total impulse
zero
