Physics concepts ch. 6 and 7
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? (a) Above it (b) Below it (c) Exactly at the halfway point
(a) Above it
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.
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.
(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.
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.
(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) ves; (b) yes - (a) yes: (b) no - (a) no; (b) yes - (a) no; (b) no
(a) no; (b) yes
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,
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 6.0 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 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 6.0 m/s (b) Exactly 6.0 m/s (c) Between 0 m/s and 6.0 m/s (d) 0 m/s
(b) Exactly 6.0 m/s
Two forces F1 and F2 are acting on the box shown in CYU Figure 6.1, causing the box to move across the floor. The two force vectors are drawn to scale. Which one of the following statements is correct? this is the box-->[] F2 is angled / as if you were pulling a wagon. F1 is horizontal ---- (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.
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
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.
Concept Simulation 7.1 at www.wiley.com/college/cutnell 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) Newton's second law (c) Newton's third law (d) The principle of conservation of linear momentum
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
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.
Concept Simulation 7.2 at www.wiley.com/college/cutnell illustrates the concepts that are involved in this question. Also review Multiple-Concept Example 8. Suppose two objects collide head on, as in Example 8, 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, 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) Object 1 stops completely, while object 2 acquires the same velocity (magnitude and direction) that object 1 had before the collision.
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
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 (a) positive, (b) zero, or (c) negative work on the ball?
(c) negative work on the ball
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.
CYU Figure 6.2 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. Fuel tank is on the bottom of the jet. Jet A is flying horizontally to the left ---- Jet B is nose diving / <-- looks kinda like that lol Jet C is flying up \ <-- looks kinda like that (a) A (b) B (c) C (d) Each tank hits the ground with the same speed.
(d) Each tank hits the ground with the same speed.
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
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.
A tennis ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. Which statement is true concerning this situation? A) The momentum of the ball and the momentum of the earth both change. B) Neither the momentum of the ball nor the momentum of the earth changes. C) The momentum of the ball is changed; and the momentum of the earth is not changed. D) The momentum of the ball is unchanged; and the momentum of the earth is changed. E) Both the momentum and the kinetic energy of the ball change because of the collision.
A) The momentum of the ball and the momentum of the earth both change.
A rock is dropped from a high tower and falls freely under the influence of gravity. Which one of the following statements concerning the rock as it falls is true? Neglect the effects of air resistance. A) The rock will gain an equal amount of momentum during each second. B) The rock will gain an equal amount of kinetic energy during each second. C) The rock will gain an equal amount of speed for each meter through which it falls. D) The rock will gain an equal amount of momentum for each meter through which it falls. E) The amount of momentum the rock gains will be proportional to the amount of potential energy that it loses.
A) The rock will gain an equal amount of momentum during each second.
Complete the following statement: Different types of collisions between interacting bodies are categorized on the basis of A) kinetic energy conservation. B) mechanical energy conservation. C) linear momentum conservation. D) the magnitude of the forces involved.
A) kinetic energy conservation.
Two arrows are fired simultaneously with the same speed of 30.0 m/s. Each arrow has a mass of 0.100 kg. One is fired due east and the other due south. What is the magnitude of the total momentum of this two-arrow system? A.) 4.24 kg m/s B.) 3.00 kg m/S C.) 2.12 kg m/s D.) 6.00 kg m/s
A.) 4.24 kg m/s
Which one of the following statements is true concerning momentum? A.) Momentum and impulse are measured in the same units. B.) Momentum is a force. C.) Momentum is a velocity. D.) The momentum of an object is always positive. E.) Momentum is a scalar quantity.
A.) Momentum and impulse are measured in the same units.
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? A.) decrease B.) remain the same C.) increase
A.) decrease
In which one of the following situations will there be an increase in kinetic energy? A) A projectile approaches its maximum height. B) A ball starts from rest and freely rolls downhill. C) A box is pulled across a rough floor at constant speed. D) A satellite travels in a circular orbit around the earth at fixed altitude. E) A stone at the end of a string is whirled in a horizontal circle at constant speed.
B) A ball starts from rest and freely rolls downhill.
Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice themass of the other. When the balls reach the ground, how do the kinetic energies of the two balls compare? A) The lighter one has one fourth as much kinetic energy as the other does. B) The lighter one has one half as much kinetic energy as the other does. C) The lighter one has the same kinetic energy as the other does. D) The lighter one has twice as much kinetic energy as the other does. E) The lighter one has four times as much kinetic energy as the other does
B) The lighter one has one half as much kinetic energy as the other does.
In which one of the following systems is there a decrease in gravitational potential energy? A) a boy stretches a horizontal spring B) a girl jumps down from a bed C) a crate rests at the bottom of an inclined plane D) a car ascends a steep hill E) water is forced upward through a pipe
B) a girl jumps down from a bed
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? A.) less than B.) equal to C.) greater than
B.) equal to
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.
Which one of the following statements concerning kinetic energy is true? A) Kinetic energy can be measured in watts. B) Kinetic energy is always equal to the potential energy. C) Kinetic energy is always positive. D) Kinetic energy is a quantitative measure of inertia. E) Kinetic energy is directly proportional to velocity.
C) Kinetic energy is always positive.
An object of mass 3m, initially at rest, explodes breaking into two fragments of mass m and 2m, respectively.Which one of the following statements concerning the fragments after the explosion is true? A) They will fly off at right angles. B) They will fly off in the same direction. C) The smaller fragment will have twice the speed of the larger fragment. D) The larger fragment will have twice the speed of the smaller fragment. E) The smaller fragment will have four times the speed of the larger fragment.
C) The smaller fragment will have twice the speed of the larger fragment.
Which one of the following situations is an example of an object with a non-zero kinetic energy? A) a drum of diesel fuel on a parked truck B) a stationary pendulum C) a satellite in geosynchronous orbit D) a car parked at the top of a hill E) a boulder resting at the bottom of a cliff
C) a satellite in geosynchronous orbit
Which one of the following choices is an example of a non-conservative force? A) gravitational force B) electrical force C) kinetic frictional force D) elastic spring force
C) kinetic frictional force
Two identical cars are traveling at the same speed. One is heading due east and the other due north, as the drawing shows. Which statement is true regarding the kinetic energies and momenta of the cars? A.) They have different kinetic energies and different momenta. B.) They have different kinetic energies, but the same momenta. C.) They have the same kinetic energies, but different momenta. D.) They have the same kinetic energies and the same momenta.
C.) They have the same kinetic energies, but different momenta. Kinetic energy, (1/2)mv^2, is a scalar quantity and is the same for both cars. Momentum, mv, is a vector quantity that has a magnitude and a direction. The two cars have different directions, so they have different momenta.
Where would you expect the center of mass of a baseball bat to be located? A.) halfway between the ends of the bat B.) nearer the lighter end C.) nearer the heavier end
C.) nearer the heavier end
In which one of the following situations is zero net work done? A) A ball rolls down an inclined plane. B) A physics student stretches a spring. C) A projectile falls toward the surface of Earth. D) A box is pulled across a rough floor at constant velocity. E) A child pulls a toy across a rough surface causing it to accelerate.
D) A box is pulled across a rough floor at constant velocity.
Which one of the following is characteristic of an inelastic collision? A) Total mass is not conserved. B) Total energy is not conserved. C) Linear momentum is not conserved. D) Kinetic energy is not conserved. E) The change in momentum is less than the total impulse.
D) Kinetic energy is not conserved.
A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes theenergy transformation of the rock as it rises? Neglect air resistance. A) The total energy of the rock increases. B) The kinetic energy increases and the potential energy decreases. C) Both the potential energy and the total energy of the rock increase. D) The kinetic energy decreases and the potential energy increases. E) Both the kinetic energy and the potential energy of the rock remain the same.
D) The kinetic energy decreases and the potential energy increases.
A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero newtons. Which one of the following statements concerning this event is true?A) Kinetic energy is conserved in this process. B) All of the fragments must have equal kinetic energies. C) The sum of the kinetic energies of the fragments must be zero. D) The vector sum of the linear momenta of the fragments must be zero. E) The mass of any one fragment must be equal to the mass of any other fragment
D) The vector sum of the linear momenta of the fragments must be zero.
Which one of the following has the largest kinetic energy? A) a raindrop falling B) a woman swimming C) a jet airplane flying at its maximum speed D) the earth moving in its orbit around the sun E) the space shuttle orbiting the Earth
D) the earth moving in its orbit around the sun
Complete the following statement: Momentum will be conserved in a two-body collision only if A) both bodies come to rest. B) the collision is perfectly elastic. C) the kinetic energy of the system is conserved. D) the net external force acting on the two-body system is zero. E) the internal forces of the two body system cancel in action-reaction pairs.
D) the net external force acting on the two-body system is zero.
Complete the following statement: A force that acts on an object is said to be conservative if A) it obeys Newton's laws of motion. B) it results in a change in the object's kinetic energy. C) it always acts in the direction of motion of the object. D) the work it does on the object is independent of the path of the motion. E) the work it does on the object is equal to the increase in the object's kinetic energy.
D) the work it does on the object is independent of the path of the motion.
A bicycle rider has a speed of 19.0 m/s at a height of 55.0 m above sea level when he begins coasting down hill. The mass of the rider and his bike is 88.0 kg. Sea level is the zero level for measuring gravitational potential energy. Ignoring friction and air resistance, what is the rider's total mechanical energy when he coasts to a height of 25.0 m above sea level? A.) 4.74 × 10^4 J B.) 4.18 × 10^4 J C.) 1.59 × 10^4 J D.) 6.33 × 10^4 J
D.) 6.33 × 10^44 J The total mechanical energy is the kinetic energy plus the gravitational potential energy: E = (1/2)mv^2 + mgh = (1/2)(88.0kg) (19.0m/s)^2 + (88.0kg) (9.80m/s^2) (55.0 m). Since friction and air resistance are being ignored, the total mechanical energy is conserved, which means that it has the same value, no matter what the height above sea level is.
A high-jumper, having just cleared the bar, lands on an air mattress and comes to rest. Had she landed directly on the hard ground, her stopping time would have been much shorter. Using the impulse-momentum theorem as your guide, determine which one of the following statements is correct. A.) The air mattress exerts a smaller impulse, and a smaller net average force, on the high-jumper than does the hard ground. B.) The air mattress exerts a greater impulse, and a greater net average force, on the high-jumper than does the hard ground. C.) The air mattress exerts a greater impulse, but a smaller net average force, on the high-jumper than does the hard ground. D.) The air mattress exerts the same impulse, but a smaller net average force, on the high-jumper than does the hard ground. E.) The air mattress exerts the same impulse, but a greater net average force, on the high-jumper than does the hard ground.
D.) The air mattress exerts the same impulse, but a smaller net average force, on the high-jumper than does the hard ground. According to the impulse-momentum theorem, the impulse is equal to the final momentum minus the initial momentum. Therefore, the impulses are the same in both cases, since the final momenta are the same and the initial momenta are the same. The impulse is also the product of the net average force and the time of impact. Since the impulses are equal and the time of impact is larger for the air mattress than for the ground, the air mattress exerts a smaller net average force on the high jumper.
Which one of the following choices is an example of a conservative force? A) tension B) normal force C) static frictional force D) motor propulsion force E) elastic spring force
E) elastic spring force
In which one of the following situations is linear momentum not conserved? A) A bomb suspended by a string explodes into one hundred fragments. B) A bowling ball collides with a set of ten pins. C) A golf ball is struck by a club. D) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction. E) A tree limb is struck by lightning and falls to the ground.
E) A tree limb is struck by lightning and falls to the ground.
Which one of the following statements concerning momentum is true? A) Momentum is a force. B) Momentum is a scalar quantity. C) The SI unit of momentum is kg m2/s. D) The momentum of an object is always positive. E) Momentum and impulse are measured in the same units.
E) Momentum and impulse are measured in the same units.
A stunt person jumps from the roof of a tall building, but no injury occurs because the person lands on a large,air-filled bag. Which one of the following best describes why no injury occurs? A) The bag provides the necessary force to stop the person. B) The bag reduces the impulse to the person. C) The bag increases the amount of time the force acts on the person and reduces the change in momentum. D) The bag decreases the amount of time during which the momentum is changing and reduces the average force on the person. E) The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.
E) The bag increases the amount of time during which the momentum is changing and reduces the average force on the person.
An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force. Which one of the following statements is true? A) The magnitude of the work done by the tension force is larger than that done by the gravitational force. B) The magnitude of the work done by the gravitational force is larger than that done by the tension force. C) The work done by the tension force is zero joules. D) The work done by the gravitational force is zero joules. E) The net work done by the two forces is zero joules.
E) The net work done by the two forces is zero joules.
A donkey pulls a crate up a rough, inclined plane at constant speed. Which one of the following statementsconcerning this situation is false? A) The gravitational potential energy of the crate is increasing. B) The net work done by all the forces acting on the crate is zero joules. C) The work done on the crate by the normal force of the plane is zero joules. D) The donkey does "positive" work in pulling the crate up the incline. E) The work done on the object by gravity is zero joules.
E) The work done on the object by gravity is zero joules.
Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities after the collision is necessarily true? A) They will exchange velocities. B) Their velocities will be reduced. C) Their velocities will be unchanged. D) Their velocities will be zero. E) Their velocities may be zero.
E) Their velocities may be zero.
Complete the following statement: A collision is elastic if A) the final velocities are zero. B) the objects stick together. C) the final kinetic energy is zero. D) the final momentum is zero. E) the total kinetic energy is conserved
E) the total kinetic energy is conserved
Complete the following statement: Work may be expressed using all of the following units except A) N x m. B) joule. C) erg. D) ft x lb. E) watt.
E) watt.
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.
In an elastic collision, the kinetic energy of each object is always the same before and after the collision. True False
False
Which of the following is not a nonconservative force? - Tension - Kinetic friction - Gravity - Air resistance
Gravity
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.
A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? Yes or No
No
Two identical automobiles have the same speed, one traveling east and one traveling west. Do these cars have the same momentum?
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
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.
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? (a) Final Momenta person 1: −60 kg · m/s Final Momenta person 2 and canoe: +170 kg · m/s (b) Final Momenta person 1: −30 kg · m/s Final Momenta person 2 and canoe: +110 kg · m/s (c) Final Momenta person 1: −40 kg · m/s Final Momenta person 2 and canoe: −70 kg · m/s (d) Final Momenta person 1: +80 kg · m/s Final Momenta person 2 and canoe: −30 kg · m/s
a) Final Momenta person 1: −60 kg · m/s Final Momenta person 2 and canoe: +170 kg · m/s
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.) 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 Impulse {(net average F)(Δt)}= final momentum {(mvf)} - initial momentum {(mvi)}, 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.) no b.) no
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.) no b.) the impulse of the thrust is equal in magnitude and opposite in direction to the impulse of the force due to air resistance.
A sunbather is lying on a floating raft that is stationary. 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.) yes, the opposite to the motion of the sunbather.
(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?
a.)no b.) yes
Two objects have the same momentum. Do the velocities of these objects necessarily have (a) the same directions and (b) the same magnitudes?
a.)yes b.) no
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 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 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 or 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
A person is riding on a Ferris wheel. When the wheel makes one complete turn, the net work done on the person by the gravitational force __________. - is zero - is positive - depends on the diameter of the wheel - is negative - depends on how fast the wheel moves
is zero
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, or nearer the heavier end?
near 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 sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat?
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
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.
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
