87 Created by Master Student Physics Practice Test #2 1 / 40 Which of the following is/are true concerning magnetic forces and fields? I. The magnetic field lines due to a current-carrying wire radiate away from the wire. II. The kinetic energy of a charged particle can be increased by a magnetic force. III. A charged particle can move through a magnetic field without feeling a magnetic force. I only II and III only I and II only III only I and III only I is false: The magnetic field lines due to a current-carrying wire encircle the wire in closed loops. II is also false: Since the magnetic force is always perpendicular to the charged particle's velocity vector, it can do work on the charged particle; therefore, it cannot change the particle's kinetic energy. III, however, is true: If the charged particle's velocity is parallel (or antiparallel) to the magnetic field lines, then the particle will feel no magnetic force. 2 / 40 Two equal vectors V and V' are added together. All of the following are possible values for the magnitude of the resultant vector EXCEPT 1/4 V 1/2 V 2 V 4 V The correct answer is (E). For any value of the vector V and V , they are equal in magnitude to one another. Whether they act in the same or opposite directions from one another, all the choices are possible except the value of 4 times V. 3 / 40 Refrigeration is a process through which heat is removed from the inside of the refrigerator. cold air is produced inside the refrigerator. hot air is removed from the inside of the refrigerator. hot air is changed to a cold condensate inside the refrigerator. hot air inside the refrigerator is expanded to remove its heat. The correct answer is (A). The refrigerator is essentially a heat engine that is being run in reverse. The refrigerator heats the room outside by removing heat energy from the enclosed and insulated refrigerator box. The process produces the cooling effect. 4 / 40 A photon can eject an electron from the surface of a photovoltaic metal if and only if the frequency of the photon is above the activation minimum. the wavelength of the photon is above the activation minimum. the speed of the photon is above an activation minimum. the momentum of the photon is below the activation minimum. the momentum of the impacted electron is above the activation minimum. The correct answer is (A). Electrons in photovoltaic metals are only energized by the photons that carry enough energy to dislodge the electrons. 5 / 40 Which wave characteristic describes the product of the frequency and the wavelength? Frequency Amplitude Wavelength Velocity Period The correct answer is (D). Wavelength has the units meters/wave and frequency has the units waves/second. The product of the two produces a velocity unit 6 / 40 A rocket is launched into the air during a fireworks show. Which of the following statements about the parts of the rocket is appropriate immediately after the explosion? They have less mass than they had before the explosion. They have more momentum than they had before the explosion. They have less momentum than they had before the explosion. They have the same momentum as they had before the explosion. They have less kinetic energy than they had before the explosion. The correct answer is (D). The momentum before the explosion must equal the momentum after the explosion. Initially, the momentum of the parts was zero; therefore, all the parts moving in all directions could be added together, and they would equal the momentum before the explosion: zero! 7 / 40 At the surface of the earth, an object of mass m has weight w. If this object is transported to an altitude that's twice the radius of the earth, then, at the new location, its mass is m and its weight is its mass is and its weight is its mass is m and its weight is its mass is and its weight is its mass is m and its weight is Mass is an intrinsic property of an object and does not change with location. This eliminates A and C. If an object's height above the surface of the earth is equal to 2RE, then its distance from the center of the earth is 3RE. Thus, the object's distance from the earth's center increases by a factor of 3, so its weight decreases by a factor of 32 = 9. 8 / 40 Einstein's theory of relativity states that all the laws of nature are the same in accelerating reference frames. constant velocity reference frames. oscillating reference frames. vibrating reference frames. circling reference frames. The correct answer is (B). This statement is one of Einstein抯 postulates to the theory of relativity. 9 / 40 The driver of an automobile traveling at 80 km/hr locks his brakes and skids to a stop in order to avoid hitting a deer in the road. If the driver had been traveling at 40 km/hr, how much faster would he have stopped? 4 times the distance 2 times the distance 1/2 the distance 1/4 the distance Not enough information to tell The correct answer is (D). The same car traveling at twice the velocity has four times the energy. Constant frictional force from the tires will therefore require four times the stopping distance. The car moving at the lower rate only requires 1/4 the stopping distance. 10 / 40 Which of the following best describes the condition of an enclosed gas during an adiabatic compression? The internal energy of the gas increases. Work is done by the gas. Work is done on the gas. The gas remains at a constant temperature. The temperature of the gas decreases The correct answer is (C). An adiabatic process is one during which no heat enters or leaves the system. Work is done on the system (the compression of the gas) that keeps the heat content of the system constant. 11 / 40 The electric field strength at a point some distance away from a source charge does NOT depend on the magnitude of the source charge. the sign of the source charge. the distance from the source charge. the nature of the medium surrounding the source charge. None of the above The strength of the electric field at a point that is a distance r from a point charge of magnitude Q is given by the expression . If the source charge is surrounded by an insulating medium other than vacuum, then the value of k we use in this expression is actually , where k0 is Coulomb's constant and K is the dielectric constant of the medium. The sign of the source charge will affect the direction of the electric field vector at a point but not the strength of the field. 12 / 40 A father holds his child on his shoulders during a parade. The father does no work during the parade because no force acts on the child. the momentum of the child is constant. the potential energy of the child is gravitational. the child's kinetic energy is constant. the child's distance from the ground remains the same. The correct answer is (E). The father holds the child at the same distance from the ground. If there is displacement, there is no work done. 13 / 40 Negative charges are accelerated by electric fields toward points at lower electric potential at higher electric potential where the electric field is zero where the electric field is weaker where the electric field is stronger 4 B Use the definition ∆V = -. If an electric field accelerates a negative charge doing positive work on it, then WE > 0. If q < 0, then - is positive. Therefore, ∆V is positive, which implies that V increases. 14 / 40 A pair of tuning forks produce sound waves that travel through the air. The frequency of the sound waves produced by the first tuning fork is 440 Hz, and the frequency of the sound waves produced by the second tuning fork is 880 Hz. If v1 denotes the speed of the sound waves produced by the first tuning fork and v2 denotes the speed of the sound waves produced by the second turning fork, then v1 = 2v2 v1 = 4v2 v1 = v2 v2 = 2v1 v2 = 4v1 The speed of a wave is determined by the properties of the medium, not by the frequency. (An exception to this general rule includes light through a transparent material medium such as glass ”the speed depends slightly on the frequency, and this accounts for the phenomenon of dispersion, which can be seen in the familiar spreading of white light into its component colors when it passes through a prism.) Since wave speed is independent of frequency in the situation described here, the answer is C. 15 / 40 What is the major product of the fission reaction of 235 U? The basic fission reaction is Protons Neutrons Radiation Heat Light The correct answer is (D). The reactors produce heat, which in turn changes water to steam, which is used to turn the turbines to generate electricity. 16 / 40 A photovoltaic metal absorbs a photon of yellow light and immediately emits an ultraviolet photon. This is called fluorescence. influorescence. phosphorescence. photoluminescence. This is not possible. The correct answer is (E). The photon of yellow light does not contain enough energy to cause the metal to emit an ultraviolet photon. Remember the energy of a photon is directly related to the frequency of the electromagnetic radiation. The higher the frequency, the higher the energy of the photon of the radiation. Ultraviolet light has a much higher frequency than yellow light, thus its photon is more energetic. 17 / 40 A 400N box is suspended motionless from a steel frame by two ropes, A and B, which hang straight up and down. Which of the following statements about the tension in the two ropes is correct? The tension in rope A is larger than in rope B. The tension in rope B is larger than in rope A. The tension in the two ropes is greater than 400N. The tension in the two ropes is less than 400N. The tension in the two ropes is equal to 400N. The correct answer is (E). According to the first condition of equilibrium, the sum of all the applied forces must equal zero if an object is not to move. 18 / 40 A person who normally weighs 900N at sea level climbs to the top of Mt. Everest. While on top of Mt. Everest that person will weigh zero. approximately 900N. considerably less than 900N but more than zero. considerably more than 900N. Need more information. The correct answer is (B). Although the person has moved further from the center of the earth, that person now has the additional mass of Mt. Everest under him. i. Point the thumb of the right hand in the direction of the current or the motion of the particle. iii. The palm of the right hand points in the direction of the applied force. 19 / 40 Which of the following statements is/are correct about an object that has no unbalanced forces applied to it? I. The object has no velocity. II. The object has no acceleration. III. The object does not move. I only II only I and III only II and III only I, II, and III The correct answer is (B). If there is no unbalanced force applied to an object, the object is not accelerated. An unbalanced force always causes acceleration of the object to which it is applied. 20 / 40 What is the centripetal acceleration on the rim of a wagon wheel of 44 cm diameter if the wagon is being pulled at a constant 2.5 m/s? 10.8 m/s 18.6 m/s 28.4 m/s 32.7 m/s 36.3 m/s The correct answer is (C). The centripetal acceleration is found with the following equation: 21 / 40 Which of the following would be half as great at a distance of 2R from a source charge than it would be at a distance of R from the charge? I. Electric force on another charge II. Electric field due to the source charge III. Electric potential due to the source charge I only II only III only I and II only I, II, and III 5 C Both electric force and electric field obey inverse square laws. The equation for electric force is F = , and the equation for electric field is E = . Thus, both of these would be one-quarter as great at twice the distance. However, electric potential is just an inverse. The equation for electric potential is (notice that the r is not squared). Thus, at twice the distance, it would be half as great. Thus, only Roman numeral III is true. 22 / 40 An observer is 2 m from a source of sound waves. By how much will the sound level decrease if the observer moves to a distance of 20 m ? 1 dB 2 dB 10 dB 18 dB 20 dB The intensity (power per unit area) is proportional to 1/r2, where r is the distance between the source and the detector. If r increases by a factor of 10, the intensity decreases by a factor of 100. Because the decibel scale is logarithmic, if the intensity decreases by a factor of 100 = 102, the decibel level decreases by 10 log (102) = 20 dB. 23 / 40 A 12,500 kg boxcar rolling through a freight yard has a velocity of 1 m/s when it strikes another boxcar of the same mass that is at rest. Both cars stick together and continue to roll down the track with a momentum of 0 kg·m/s 3125 kg· m/s 6250 kg·m/s 12,500 kg·m/s 25,000 kg·m/s The correct answer is (D). This is a conservation of momentum question. Since the momentum before an event must equal the momentum after an event, the momentum must be 12,500 kg·m/s. 24 / 40 A battery and a variable resistor are in series with a small fan. A switch is closed, and the fan runs. When the variable resistor is moved slightly to the left, the fan slows down a little. When the variable resistor is moved slightly to the right, the fan speeds up a little. The following question is about the operation of the circuit described. If the variable resistor in the circuit is set all the way to the right, what happens in the circuit? I. The fan runs faster. II. The voltage decreases. III. The current increases. I only II only I and III only II and III only I, II, and III The correct answer is (C). When the variable resistor is moved toward the right, more of the resistance value of the variable resistor is bypassed which means there is less resistance in the circuit. A decrease in the resistance of a circuit allows more current to flow (Ohm's Law). Since there is more current flowing in the circuit the fan has more current flowing through it too, and the fan runs faster. 25 / 40 Two objects, one of mass 3 kg and moving with a speed of 2 m/s and the other of mass 5 kg and speed 2 m/s, move toward each other and collide head-on. If the collision is perfectly inelastic, find the speed of the objects after the collision. 0.25 m/s 0.5 m/s 0.75 m/s 1 m/s 2 m/s By definition of perfectly inelastic, the objects move off together with one common velocity, v ², after the collision. By conservation of linear momentum, 26 / 40 A laboratory centrifuge starts from rest and reaches a rotational speed of 8,000 radians/ sec in a time of 25 seconds. What is the angular acceleration of the centrifuge? 160 radians/sec2 320 radians/sec2 640 radians/sec2 10,000 radians/sec2 20,000 radians/sec2 The correct answer is (B). The angular acceleration is found by dividing the change in angular velocity by the change in time: 27 / 40 The symbols used in writing nuclear equations. Atomic nuclei are typically written in the form . Which letter represents the protons plus neutrons in the nucleus? The number of protons is Z. The number of neutrons is X. The symbol of the element is X. The number of electrons is A. The mass number is A. The correct answer is (E). The number of protons added to the number of neutrons is equal to the mass number of an atom. The mass is represented by the letter A. 28 / 40 A rope of length 5 m is stretched to a tension of 80 N. If its mass is 1 kg, at what speed would a 10 Hz transverse wave travel down the string? 2 m/s 5 m/s 20 m/s 50 m/s 200 m/s The speed of a transverse traveling wave on a stretched rope is given by the equation v = . Therefore 29 / 40 Which is due to the change in wave speed when a wave strikes the boundary to another medium? Reflection Refraction Polarization Diffraction Interference Refraction, the change in the direction of a wave when it enters a new medium, is caused by the change in the speed of the wave as it travels within the new medium. 30 / 40 A negative ion is an object that has more electrons than neutrons. more electrons than protons. more protons that neutrons. more protons than electrons. more neutrons than electrons or protons. The correct answer is (B). A negative ion is an object that has an excess of electrons. Electrons are the negatively charged part of the atom, therefore they give an object that carries excess of electrons a negative charge. 31 / 40 A rocket sled rides on a frictionless track while a 1000N force from the rockets accelerates the sled. Suddenly the retrorockets accidentally fire, applying a 1000N force in the opposite direction. The sled will slow down gradually to a stop. continue to accelerate. move at a constant speed. reverse direction. not be affected at all. The correct answer is (C). The rocket sled is already moving. The two rocket engines apply two (different pairs) of forces of equal magnitude to the same object but in different directions. There is therefore no unbalanced force and the sled continues in its state of motion. 32 / 40 A straight wire of length 2 m carries a 10-amp current. How much stronger is the magnetic field at a distance of 2 cm from the wire than it is at 4 cm from the wire? 2 2 4 4 8 The strength of the magnetic field at a distance r from a long, straight wire carrying a current I is proportional to I /r; that is, B is inversely proportional to r. So, at the distance from the wire, the magnetic field will be twice as strong. 33 / 40 The mass of the atom is equally dispersed throughout the entire atom cloud. equally divided between all its parts: the electrons, neutrons, and protons. concentrated in the orbital cloud. concentrated in the nucleus. determined by spectroscopic analysis. The correct answer is (D). Rutherford found that most of the mass of an atom is concentrated in the nucleus of the atom. 34 / 40 Two children are riding a merry-go-round. Child (P) rides on a pony on the outside rim of the merry-go-round, while Child (L) rides a lion on the inside rim of the merry-goround. At the end of the ride, which of the following statements is true? Child (P) had the largest angular displacement. Child (L) had the largest tangential displacement. Child (P) had the largest tangential velocity. Child (L) had the largest angular velocity. Child (L) had the largest linear acceleration The correct answer is (C). The tangential velocity is the product of the angular velocity and the radius of the object or the person from the center of the rotating device. Both children have the same angular velocity, but the child on the pony is farther from the center of the merry-go-round. 35 / 40 Why do baseball catchers wear mitts rather than just using their bare hands to catch pitched baseballs? The impulse delivered to the catcher's hand is reduced due to the presence of the mitt. The force on the catcher's hand is reduced because of the increased area provided by the mitt. The baseball's change in momentum is reduced due to the presence of the mitt. The force on the catcher's hand is reduced because the mitt increases the time of impact. The force on the catcher's hand is reduced because the mitt decreases the time of impact. The impulse delivered to the ball is equal to the ball's change in momentum, and the presence of the mitt does not change this, eliminating A and C. The extra area may decrease the pressure on the catcher's hand, but not the force (eliminating B). The padding of the mitt causes the time during which the ball comes to a stop to increase (just as an air bag increases the time it takes for an automobile passenger involved in an accident to come to a stop), which decreases the magnitude of the ball's acceleration (since a = (delta)v/(delta)t). A decrease in the magnitude of the acceleration means a decrease in the magnitude of the force (since a = F/m). 36 / 40 The current through a 20ohm resistor connected to a 12V battery is .3 amperes. .6 amperes. .9 amperes. 1.6 amperes. 1.9 amperes. The correct answer is (B). According to Ohm's Law, the current is equal to I = V/r. Solving for the current, we have 12V/20ohm = .6 ampere. 37 / 40 ater has the specific heat 4.186 kJ/kg* degrees celsius, a boiling point of 100 degrees celsius, and a heat of vaporization of 2,260 kJ/kg. A sealed beaker contains 100 g of water that's initially at 20 degrees celsius. If the water absorbs 100 kJ of heat, what will its final temperature be? 100 degrees celsius 119 degrees celsius 143 degrees celsius 183 degrees celsius 239 degrees celsius First, let's figure out how much heat is required to bring the water to its boiling point. 38 / 40 An Olympic diver performs a 3.5 somersault. During his dive he uses the tuck position so that he will have larger angular momentum. smaller angular momentum. larger rotational rate. smaller rotational rate. longer time in the air. The correct answer is (C). The diver needs to complete the rotations as quickly as possible. The tuck position reduces the moment of inertia of the diver's body, allowing the diver to spin at a higher rate. 39 / 40 When green light (wavelength = 500 nm in air) travels through diamond (refractive index = 2.4), what is its wavelength? 208 nm 357 nm 500 nm 700 nm 1,200 nm The frequency is unchanged, but because the speed of light in diamond is less than in air, the wavelength of the light in diamond is shorter than its wavelength in air. 40 / 40 A toy rocket is launched straight up. At the exact top of its flight path, which of the following is true? Its velocity and acceleration are zero. Its velocity is zero and acceleration is 9.8 m/s2. Its velocity is 9.8 m/s and acceleration is 9.8 m/s2. Its velocity is 9.8 m/s and acceleration is zero. Its velocity is 9.8 m/s and displacement is 9.8 m. The correct answer is (B). The toy rocket achieves zero velocity at the exact top of its flight when it is not moving upward nor is it moving downward. It is constantly accelerated toward the earth while it is in free fall. Your score is The average score is 42% LinkedIn Facebook Twitter VKontakte 0% Restart quiz Previous Quiz Next Quiz
