Physics 2113 Final
b (work is path dependent)
Rocket force and Air Resistance are a... a) Conservative force b) Non-Conservative force
b
A ball is whirled on the end of a string in a horizontal circle of radius R at constant speed v. Complete the following statement: The centripetal acceleration of the ball can be increased by a factor of 4 by a) keeping the speed fixed and increasing the radius by a factor of 4. b) keeping the speed fixed and decreasing the radius by a factor of 4. c) keeping the radius fixed and increasing the speed by a factor of 4. d) keeping the radius fixed and increasing the period by a factor of 4. e) keeping the radius fixed and decreasing the period by a factor of 4.
d
A baseball is hit upward and travels along a parabolic arc before it strikes the ground. Which one of the following statements is necessarily true? a) The acceleration of the ball decreases as the ball moves upward. b) The velocity of the ball is a maximum when the ball is at the highest point in the arc. c) The velocity of the ball is zero m/s when the ball is at the highest point in the arc. d) The x-component of the velocity of the ball is the same throughout the ball's flight. e) The acceleration of the ball is zero m/s2 when the ball is at the highest point in the arc.
c (The centripetal force is directed along the radius and toward the center of the circular path. The component FNsinθ of the normal force is directed along the radius and points toward the center of the path.)
A car is rounding a circular curve of radius r on a banked turn. As the drawing indicates, there are two forces acting on the car, its weight mg and the normal force FN exerted on it by the road. Which force, or force component, provides the centripetal force that keeps the car moving on the circular path? a) The weight, mg, of the car. b) The vertical component, FNcosθ of the normal force. c) The horizontal component, FNsinθ of the normal force. d) Both the normal force, FN, and the weight, mg, of the car. e) The normal force, FN.
e
A car is traveling in uniform circular motion on a section of flat roadway whose radius is r. The road is slippery, and the car is just on the verge of sliding off the roadway. If the car's speed were now doubled, what would be the smallest radius of the curve it could drive on without slipping? a) r/2 b) r c) r/4 d) 2r e) 4r
c (The hallmark of an object in equilibrium is that it has no acceleration. Therefore, an object in equilibrium need not be at rest. It can be moving with a constant velocity.)
A certain object is in equilibrium. Which one of the following statements is not true? a) The object has no acceleration. b) The object has a constant velocity. c) The object must be at rest. d) No net force acts on the object.
b (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.)
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? a) Yes b) No
e (Newton's first law states that an object continues in a state of rest or in a state of motion at a constant speed along a straight line, unless compelled to change that state by a net force. All three statements are consistent with the first law.)
A cup of coffee is sitting on a table in a recreational vehicle (RV). The cup slides toward the rear of the RV. According to Newton's first law, which one or more of the following statements could describe the motion of the RV? (A) The RV is at rest, and the driver suddenly accelerates. (B) The RV is moving forward, and the driver suddenly accelerates. (C) The RV is moving backward, and the driver suddenly hits the brakes. a) A b) B c) C d) A and B e) A, B, and C
c
A football is kicked at an angle Ө with respect to the horizontal. Which one of the following statements best describes the acceleration of the football during this event if air resistance is neglected? a) The acceleration is zero m/s2 when the football has reached the highest point in its trajectory. b) The acceleration is positive as the football rises, and it is negative as the football falls. c) The acceleration is 9.8 m/s2 at all times. d) The acceleration starts at 9.8 m/s2 and drops to some constant lower value as the ball approaches the ground. e) The acceleration is zero m/s2 at all times.
c (The work is given by W = (F cos θ)s, which is zero when F = 0 N, s = 0 m, or θ = 90°.)
A force F acts on an object undergoing a displacement s, the force being oriented at an angle θ with respect to the displacement. Which one of the following correctly describes ALL of the circumstances under which the work done by the force is zero? a) The force is zero, or the angle is 90°. b) The displacement is zero, or the angle is 90°. c) The force is zero, or the displacement is zero, or the angle is 90°. d) The force is zero, or the displacement is zero, or the angle is 180°. e) The force is zero, or the displacement is zero.
c
A man stands on a spring scale in a moving elevator and notices that the scale reading is 20% larger than when he weighs himself in his bathroom. Which statement can not be true? a) The elevator could be moving upward with increasing speed. b) The elevator could be moving downward with decreasing speed. c) The elevator could be moving upward at constant speed. d) The tension in the supporting cable must exceed the weight of the elevator and its contents. e) The speed of the elevator changes by equal amounts in equal times.
c (The gravitational force is a conservative force, and a conservative force does no net work on an object moving around a closed path.)
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 ____________. a) is positive b) depends on the diameter of the wheel c) is zero d) is negative e) depends on how fast the wheel moves
c
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? a) The first bullet b) The second bullet c) Both bullets
c
A rock is suspended from a string and moves downward at constant speed. Which statement is true concerning the tension in the string if air resistance is ignored? a) The tension points downward. b) The tension is greater than the weight of the rock. c) The tension is equal to the weight of the rock. d) The tension is less than the weight of the rock. e) The tension is zero newtons.
b
A rock is suspended from a string; and it accelerates downward. Which one of the following statements concerning the tension in the string is true? a) The tension is greater than the weight of the rock. b) The tension is less than the weight of the rock. c) The tension is independent of the magnitude of the rock's acceleration. d) The tension is equal to the weight of the rock. e) The tension points downward.
e (Potential energy increases with respect to height. But the total energy is conserved.)
A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance. a) Both the potential energy and the total energy of the rock increase. b) The total energy of the rock increases. c) The kinetic energy increases and the potential energy decreases. d) Both the kinetic energy and the potential energy of the rock remain the same. e) The kinetic energy decreases and the potential energy increases.
b (The acceleration (known as the centripetal acceleration) and the net force (known as the centripetal force) have the same direction and point toward the center of the circular path.)
A small cylinder rests on a circular turntable that is rotating clockwise at a constant speed. Which set of vectors gives the direction of the velocity *v* and acceleration *a* of the cylinder, and the net force ΣF that acts on it. a) 2 b) 4 c) 3 d) 1
b
A solar-powered car is traveling at constant speed around a circular track. What happens to the centripetal acceleration of the car if the speed is doubled? a) The centripetal acceleration is decreased by a factor of one-fourth. b) The centripetal acceleration increases by a factor of 4. c) The centripetal acceleration is decreased by a factor of one-half. d) The centripetal acceleration increases by a factor of 2. e) The centripetal acceleration remains the same.
a
A spaceship is in orbit around the earth at an altitude of 12 000 miles. Which one of the following statements best explains why the astronauts experience "weightlessness"? a) The spaceship is in free fall and its floor cannot press upwards on the astronauts. b) The force of gravity decreases as the inverse square of the distance from the earth's center. c) The centripetal force of the earth on the astronaut in orbit is zero newtons. d) The pull of the earth on the spaceship is canceled by the pull of the other planets. e) The force of the earth on the spaceship and the force of the spaceship on the earth cancel because they are equal in magnitude but opposite in direction.
b
A stone is tied to a string and swung along the path of a vertical circle at constant speed. When is the string most likely to break? a) The string is equally likely to break for any position of the stone. b) When the stone is at the very bottom of the circle. c) When the stone is at the very top of the circle. d) When the string is horizontal.
c
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? a) The ball's speed is constant so the minimum and maximum speed occurs at every point. b) The minimum speed occurs at the lowest point and the maximum occurs at the highest. c) The maximum speed occurs at the lowest point and the minimum occurs at the highest.
b
A tennis ball is thrown upward at an angle from point A. It follows a parabolic trajectory and hits the ground at point D. At the instant shown, the ball is at point B. Point C represents the highest position of the ball above the ground. Which statement is true concerning the ball when it is at C, the highest point in its trajectory? a) The ball's velocity is zero, but its acceleration is not zero. b) The ball's velocity is perpendicular to its acceleration. c) The horizontal and vertical components of the ball's velocity are equal. d) The ball's velocity is not zero, but its acceleration is zero. e) The ball's velocity and acceleration are both zero.
d
A tennis ball is thrown upward at an angle from point A. It follows a parabolic trajectory and hits the ground at point D. At the instant shown, the ball is at point B. Point C represents the highest position of the ball above the ground. While in flight, how do the x and y components of the velocity vector of the ball compare at the points A and D? a) The velocity components are non-zero at A and are zero m/s at D. b) The velocity components have the same magnitudes at both points, but the directions of the x components are reversed. c) The velocity components are the same in magnitude and direction at both points. d) The velocity components have the same magnitudes at both points, but the directions of the y components are reversed. e) The velocity components have the same magnitudes at both points, but their directions are reversed.
e
A tennis ball is thrown upward at an angle from point A. It follows a parabolic trajectory and hits the ground at point D. At the instant shown, the ball is at point B. Point C represents the highest position of the ball above the ground. While in flight, how do the x and y components of the velocity vector of the ball compare at the points B and C? a) The x component is larger at C than at B; the y component at B points up while at C, it points downward. b) The x components are the same; the y component has a larger magnitude at C than at B. c) The x component is larger at B than at C; the y component at B points down while at C, it points upward. d) The velocity components are non-zero at B and zero at C. e) The x components are the same; the y component at C is zero m/s.
c (Since air resistance always opposes the motion, it is a force that is always directed opposite to the displacement. Therefore, negative work is done.)
Air resistance is a nonconservative force. It always opposes the motion of an object. An airplane flies from New York to Atlanta and then returns to its point of departure. The net work done by air resistance during this round trip ___________. a) is negative for higher speeds and positive for slower speeds b) is positive c) is negative d) is negative for slower speeds and positive for higher speeds e) is zero
c
An astronaut orbits the earth in a space capsule whose height above the earth is equal to the earth's radius. How does the mass of the astronaut in the capsule compare to her mass on the earth? a) Her mass is approximately equal to one-sixteenth her mass on earth. b) Her mass is approximately equal to one-third of her mass on earth. c) Her mass is equal to her mass on earth. d) Her mass is approximately equal to one-half of her mass on earth. e) Her mass is approximately equal to one-fourth her mass on earth.
b (since the speed is constant, then net force would be equal to zero, from newtons first law of motion, and work is define as net force *displacement, then therefore net work is zero also.)
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 net work done by the two forces is zero joules. c) The magnitude of the work done by the gravitational force is larger than that done by the tension force. d) The work done by the tension force is zero joules. e) The work done by the gravitational force is zero joules.
a (If only one force acts on the object, it is the net force; thus, the net force must be nonzero. Consequently, the velocity would change, according to Newton's first law, and could not be constant.)
An object is moving at a constant velocity. All but one of the following statements could be true. Which one cannot be true? a) A single force acts on the object. b) No forces act on the object. c) Three forces act simultaneously on the object. d) Two forces act simultaneously on the object.
d
An object is thrown upward at an angle Ө above the ground, eventually returning to earth. Which statement is true? a) The velocity and acceleration are always parallel. b) The velocity and acceleration are parallel only at the top of the trajectory. c) The velocity and acceleration are always perpendicular. d) The velocity and acceleration are perpendicular only at the top of the trajectory.
c
An object is undergoing uniform circular motion. Which of the following changes would increase the period of the motion? I. Increase the radius of the circular motion. II. Decrease the radius of the circular motion. III. Increase the speed of the object. IV. Decrease the speed of the object. a) I only b) II only c) I and IV d) IV only e) III only f) I and III
e
An object is undergoing uniform circular motion. Which of the following is/are true? I. The object is moving at constant velocity. II. The object is moving at constant speed. III. The object is accelerating. a) I and III b) I only c) III only d) I and II e) II and III f) II only
b
Can two nonzero perpendicular vectors be added together so their sum is equal to zero? a) Yes b) No
b
Complete the following statement: A force that acts on an object is said to be conservative if a) it always acts in the direction of motion of the object. b) the work it does on the object is independent of the path of the motion. c) it results in a change in the object's kinetic energy. d) the work it does on the object is equal to the increase in the object's kinetic energy. e) it obeys Newton's laws of motion.
b
Complete the following statement: The maximum speed at which a car can safely negotiate an unbanked curve depends on all of the following factors except a) the coefficient of static friction between the road and the tires. b) the coefficient of kinetic friction between the road and the tires. c) the ratio of the static frictional force between the road and the tires and the normal force exerted on the car. d) the diameter of the curve. e) the acceleration due to gravity.
e
Complete the following statement: The term net force most accurately describes a) the quantity that causes a displacement. b) the mass of an object. c) the inertia of an object. d) the quantity that keeps an object moving. e) the quantity that changes the velocity of an object.
d (Work is positive when the force has a component in the direction of the displacement. The force shown has a component along the -x and along the +y axis. Therefore, displacements in these two directions involve positive work.)
Consider the force F shown in the drawing. This force acts on an object that can move along the positive or negative x axis, or along the positive or negative y axis. The work done by this force is positive when the displacement of the object is along the __________ axis or along the __________ axis. a) +x, +y b) +x, -y c) -x, -y d) -x, +y
d
Consider the vector equation A + B = C. The component method of vector addition specifies that the scalar components of the resultant vector C are given by Cx = Ax + Bx and Cy = Ay + By. Which of the following would give the magnitude of the resultant vector C? a) Cx + Cy b) Cx - Cy c) Cx^2 + Cy^2 d) Sqrt( Cx^2 + Cy^2) e) None of the above
b (The acceleration of a projectile is the same at all points on the trajectory. It points downward, toward the earth, and has a magnitude of 9.80 m/s2.)
Each drawing shows three points along the path of a projectile, one on its way up, one at the top, and one on its way down. The launch point is on the left in each drawing. Which drawing correctly represents the acceleration a of the projectile at these three points? a) 3 b) 4 c) 5 d) 1 e) 2
a (work is path independent)
Electrical Force is a ... a) Conservative force b) Non-Conservative force
b (work is path dependent)
Friction is a... a) Conservative force b) Non-Conservative force
a (work is path independent)
Gravity is a ... a) Conservative force b) Non-Conservative force
d
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) A nonzero net external force acts on the object in both cases. b) A nonzero net external force acts on the object in neither case. c) A nonzero net external force acts on the object in Case A only. d) A nonzero net external force acts on the object in Case B only.
c (Although the "rough floor" may trick you into believing there is frictional force, since it is moving at a constant velocity, the Kinetic Energy is 0, therefore there is 0 net work done)
In which one of the following situations is zero net work done? a) A ball rolls down an inclined plane. b) A projectile falls toward the surface of Earth. c) A box is pulled across a rough floor at constant velocity. d) A physics student stretches a spring. e) A child pulls a toy across a rough surface causing it to accelerate.
a
In which one of the following situations will there be an increase in kinetic energy? a) A ball starts from rest and freely rolls downhill. b) A box is pulled across a rough floor at constant speed. c) A stone at the end of a string is whirled in a horizontal circle at constant speed. d) A projectile approaches its maximum height. e) A satellite travels in a circular orbit around the earth at fixed altitude.
a (gravitational potential energy is given by m*g*h where [m=mass,g=acceleration due to gravity and h= height above the surface of the earth] here,the height 'h' is decreasing when the girl jumps down from the bed)
In which one of the following systems is there a decrease in gravitational potential energy? a) a girl jumps down from a bed b) a boy stretches a horizontal spring 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 (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.)
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? a) Yes b) No
b (work is path dependent)
Normal Force is a... a) Conservative force b) Non-Conservative force
b
Only one of the following is possible for a moving object. Which one? a) The velocity is constant at all times, and the acceleration is not zero. b) The velocity is zero at one instant, and the acceleration is not zero at that instant. c) The velocity is directed eastward and is increasing, while the acceleration is directed westward. d) The velocity is directed eastward and is decreasing, while the acceleration is also eastward. e) The velocity is directed northward and is increasing, while the acceleration is zero
a (work is path independent)
Spring Force is a ... a) Conservative force b) Non-Conservative force
b (work is path dependent)
Tension is a... a) Conservative force b) Non-Conservative force
b (What matters is the direction of the elevator's acceleration. When the acceleration is upward, the apparent weight is greater than the true weight. When the acceleration is downward, the apparent weight is less than the true weight. In both possibilities the acceleration points upward.)
The apparent weight of a passenger in an elevator is greater than his true weight. Which one of the following is true? a) The elevator is either moving upward with a decreasing speed or moving downward with an increasing speed. b) The elevator is either moving upward with an increasing speed or moving downward with a decreasing speed. c) The elevator is either moving upward with an increasing speed or moving upward with a decreasing speed. d) The elevator is either moving upward with an increasing speed or moving downward with an increasing speed. e) The elevator is either moving upward with a decreasing speed or moving downward with a decreasing speed.
d (According to Newton's second law, the net force, FN - mg, must equal the mass m times the centripetal acceleration v2/r.)
The drawing shows an extreme skier at bottom of a ski jump. At this point the track is circular with a radius r. Two forces act on the skier, her weight mg and the normal force FN. Which relation describes how the net force acting on her is related to her mass m and speed v and to the radius r? Assume that "up" is the positive direction. a) Fn = (mv^2)/r b) Fn + mg = (mv^2)/r c) -mg = (mv^2)/r d) Fn - mg = (mv^2)/r
b (The horizontal component vx of the projectile's velocity remains constant throughout the motion, since the acceleration ax in the horizontal direction is zero (ax = 0 m/s2,). The vertical component vy, however, changes as the projectile moves. This component is greatest at point 1, decreases to zero at point 2 at the top of the trajectory, and then increases to a magnitude less than that at point 1 as the projectile approaches point 3.)
The drawing shows projectile motion at three points along the trajectory. The speeds at the points are v1, v2, and v3. Assume there is no air resistance and rank the speeds, largest to smallest. a) v1 > v2 > v3 b) v1 > v3 > v2 c) v3 > v2 > v1 d) v2 > v3 > v1 e) v2 > v1 > v3
c (The statement is true because 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).)
The net external force acting on an object is zero. Which one of the following statements is true? a) The object can only be stationary. b) The object can only be traveling with a constant velocity. c) The object can be either stationary or traveling with a constant velocity. d) The object can only be traveling with a velocity that is changing.
c
The same force F pushes in three different ways on a box moving with a velocity v, as the drawings show. Rank the work done by the force F in ascending order (smallest first). a) A, B, C b) C, B, A c) C, A, B d) B, A, C e) A, C, B
c (The work-energy theorem indicates that when the net force acting on the particle does negative work, the kinetic energy decreases. Since each force does negative work, the work done by the net force must be negative, and the kinetic energy must decrease. But when the kinetic energy decreases, the speed must also decrease, since the kinetic energy is proportional to the square of the speed. Since it is stated that the speed increases, this answer is not possible)
Two forces F1 and F2 act on a particle. As a result the speed of the particle increases. Which one of the following is NOT possible? a) The work done by each force is positive. b) The work done F1 by is zero, and the work done by F2 is positive. c) The work done by each force is negative. d) The work done by F1 is positive, and the work done by F2 is zero. e) The work done by F1 is positive, and the work done by F2 is negative.
e
Two identical blocks are pulled along a rough surface as suggested in the figure. Which one of the following statements is false? a) The normal force exerted on the blocks by the surface is the same for both blocks. b) A force of the same magnitude is needed to keep each block moving. c) The coefficient of kinetic friction is the same in each case. d) A force of the same magnitude was required to start each block moving. e) The magnitude of the force of kinetic friction is greater for the block on the right.
d (m2 has greater mass than m1, which tends to make its gravitational force bigger, but m2 is closer to m3, which tends to make its gravitational force bigger, so these two factors will cancel and the net force will be zero.)
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? a, b, c, or d?
e
Vectors A, B, and C satisfy the following equation A + B = C, and their magnitudes are related by the scalar equation A + B = C. How is vector A oriented with respect to vector B? a) There is no way to tell the orientation of vectors A and B from the given information. b) Vectors A and B can only be equal to zero. c) Vectors A and B are perpendicular to each other. d) Vectors A and B are collinear and point in opposite directions. e) Vectors A and B are collinear and point in the same direction.
b (Displacement, being a vector, conveys information about magnitude and direction. Distance conveys no information about direction and, hence, is not a vector.)
What is the difference between distance and displacement? a) There is no difference between the two concepts; they may be used interchangeably. b) Displacement is a vector, while distance is not a vector. c) Distance is a vector, while displacement is not a vector.
c
Which force is responsible for holding a car in a frictionless banked curve? a) the vertical component of the normal force b) the horizontal component of the car's weight c) the horizontal component of the normal force d) the reaction force to the car's weight e) the vertical component of the car's weight
d
Which force is responsible for holding a car in an unbanked curve? a) the vertical component of the normal force b) the reaction force to the car's weight c) the car's weight d) the force of friction e) the horizontal component of the normal force
e
Which of the following describe nonequilibrium conditions in the context applying Newton's laws of motion? a) A spacecraft decelerating upon reentry into the atmosphere. b) A car accelerating through a traffic light. c) A ball falling off the roof of a house. d) A roller coaster going over the crest of a hill. e) All of the above.
a
Which of the following is/are true? I. The centripetal force points in toward the center of the circular motion. II. The centripetal force is independent of the object's mass. III. The centripetal force points in the opposite direction as the centripetal acceleration. IV. The centripetal force is a new and separate force created by nature, and therefore should appear in a free-body diagram. a) I only b) I and II c) I and III d) All of the above.
e
Which of the following statements is/are true? a) Physics is the most fundamental of all the branches of science. b) Physics is a very mature science, where its fundamental principles have been tested over many centuries and supported by empirical evidence from experimentation. c) Physics provides a framework for explaining the processes of the natural world. d) Physics research has had a significant impact on the development of new technologies, such as space travel, telecommunications, and medicine. e) All of the above statements are true.
c (A conservative force is a force with the property that the work done in moving a particle between two points is independent of the taken path)
Which one of the following choices is an example of a conservative force? a) normal force b) static frictional force c) elastic spring force d) tension e) motor propulsion force
c
Which one of the following choices is an example of a non-conservative force? a) elastic spring force b) electrical force c) kinetic frictional force d) gravitational force
c (This situation violates the first law, which predicts that the rabbit's foot tends to remain in place where it was when the car begins accelerating. The car would leave the rabbit's foot behind. That is, the rabbit's foot would swing away from, not toward, the windshield.)
Which one of the following descriptions violates Newton's first law of motion? a) A small suitcase is at the front of the overhead luggage compartment on an airplane. When the airplane begins its takeoff, the suitcase slides to the rear of the compartment. b) A glass of water is sitting on a table in the dining car of a train. The train brakes as it nears the station, and the glass slides forward. c) A rabbit's foot is hanging on a chain from the rearview mirror of a car. As the car accelerates, the rabbit's foot swings toward the windshield. d) A child is sitting in the back seat of a car and is not wearing a seat belt. The car is traveling forward, and the driver suddenly applies the brakes. The child flies forward against the rear side of the front seat.
b (Velocity, not speed, appears as one of the variables in the equations of kinematics. Velocity is a vector. The magnitude of the instantaneous velocity is the speed.)
Which one of the following is not a kinematic variable that appears in the equations of kinematics? a) acceleration b) speed c) displacement d) time e) velocity
e (Answers (a) and (b) are false, according to the third law, which states that whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body. It does not matter whether one of the bodies is stationary or whether it collapses. Answer (c) is false because, according to the third law, Sam and his sister experience forces of equal magnitudes during the push-off. Since Sam has the greater mass, he flies off with the smaller acceleration, according to the second law. Answer (d) is false because in catching and throwing the ball each astronaut applies a force to it, and, according to the third law, the ball applies an oppositely directed force of equal magnitude to each astronaut. These reaction forces accelerate the astronauts away from each other, so that the distance between them increases.)
Which one of the following is true, according to Newton's laws of motion? Ignore friction. a) A sports utility vehicle (SUV) hits a stationary motorcycle. Since it is stationary, the motorcycle sustains a greater force than the SUV does. b) A semitrailer truck crashes all the way through a wall. Since the wall collapses, the wall sustains a greater force than the truck does. c) Sam (18 years old) and his sister (9 years old) go ice skating. They push off against each other and fly apart. Sam flies off with the greater acceleration. d) Two astronauts on a space walk are throwing a ball back and forth between each other. In this game of catch the distance between them remains constant. e) None of the these is true, according to the third law.
c (Since the engines are shut down and since nothing is nearby to exert a force, the net force acting on the probe is zero, and its acceleration must be zero, according to Newton's second law. With zero acceleration the probe is in equilibrium.)
Which one of the following objects is in equilibrium? a) A taxi coming to a halt to discharge a passenger. b) A race horse taking off at the beginning of a race. c) A space probe with its engines shut down, moving through a vast empty region of outer space. d) A projectile as it passes through the topmost point of its trajectory. e) A brick falling from a bridge.
d
Which one of the following statements is not true? a) In the absence of air resistance the motion of a baseball after being thrown straight upward from the ground is an example of free-fall. b) The equations of kinematics apply to free-fall motion. c) In the absence of air resistance the motion of a baseball dropped from rest from the top of a building is an example of free-fall. d) Near the earth's surface the acceleration due to gravity has the approximate magnitude of 9.80 m/s2, points downward when the motion is downward, and points upward when the motion is upward. e) In free-fall motion near the earth's surface the acceleration is the acceleration due to gravity.
a
Which one of the following terms is used to indicate the natural tendency of an object to remain at rest or in motion at a constant speed along a straight line? a) inertia b) velocity c) equilibrium d) force e) acceleration
c
You and your friends are riding a rollercoaster. You enter a vertical loop-the-loop, turn upside-down, and then come out again at the bottom of the loop. This is similar to what the motorcycle stuntman did in the video. As you pass through the very bottom of the loop, do you feel heavier or lighter than normal? a) You feel lighter. b) You feel normal, just as if you were sitting at rest at your desk. c) You feel heavier.
b
You are in a car that is traveling at constant speed on a straight and level road before it suddenly starts down a hill. What can be said of your apparent weight relative to your true weight just as the car starts down the hill? a) Your apparent weight is equal to your true weight. b) Your apparent weight is less than your true weight. c) Your apparent weight is greater than your true weight.