28 Created by Master Student Physics Practice Test #10 1 / 40 A lightweight toy car crashes head-on into a heavier toy truck. Which of the following statements is true as a result of the collision? I. The car will experience a greater impulse than the truck. II. The car will experience a greater change in momentum than the truck. III. The magnitude of the acceleration experienced by the car will be greater than that experienced by the truck. I and II only II only III only II and III only I, II, and III By Newton's third law, both vehicles experience the same magnitude of force and, therefore, the same impulse; so I is false. Invoking Newton's second law, in the form impulse = change in momentum, we see that II is therefore also false. However, since the car has a smaller mass than the truck, its acceleration will be greater in magnitude than that of the truck, so III is true. 2 / 40 Which principle could be used to help calculate the amount of radiation emitted by a star? Newton's law of universal gravitation Red shift of light from other galaxies The fact that every element of atomic number greater than 83 is radioactive The zeroth law of thermodynamics Mass-energy equivalence Stars are huge nuclear-fusion reactors. When nuclei fuse, the mass of the product nucleus is less than the combined masses of the original nuclei. The missing mass has become energy, which is radiated away. Einstein's famous mass-energy equivalence equation, E = mc2, can be used to calculate the amount of energy resulting from a fusion reaction. 3 / 40 Two vectors X and Y are added together. Which of the following statements could be true? I. The resultant magnitude is smaller than X. II. The resultant magnitude is larger than Y. III. The resultant direction is the same as either X or Y. I only II only I and III only II and III only I, II, and III The correct answer is (E). If the two vectors are exactly 180 degrees apart, in each case all of the choices are a possibility. 4 / 40 A particle of charge -0.04 C is projected with speed 2e4 m/s into a uniform magnetic field, B, of strength 0.5 T. If the particle's velocity as it enters the field is perpendicular to B, what is the magnitude of the magnetic force on this particle? 4 N 8 N 40 N 80 N 400 N Since v is perpendicular to B, the strength of the magnetic force, FB, is just qvB, where q is the magnitude of the charge. In this case, then, we find that 5 / 40 A proton and an electron are each placed in an electric field between a pair of parallel plates. The electron is placed exactly halfway between the two plates, and the proton is placed midway between the electron and the negative plate. Which of the following statements is correct about the forces the particles experience? The force on the electron is larger because it has less mass. The force on the proton is larger because it has greater mass The force on the electron is larger because it is in the strongest part of the electric field. The force on the proton is larger because it is closer to the negative plate. They both experience the same force. The correct answer is (E). The electric field between a pair of parallel plates is uniform in nature. Therefore any charged particle within the field experiences the same force no matter where it is located in the field. 6 / 40 As a battery ages, its internal resistance increases. This causes the current in the external circuit to remain the same. polarize. reverse direction. increase. decrease. The correct answer is (E). The higher internal resistance in the battery leads to a reduction in the terminal potential of the battery. The lower terminal potential can produce less current in the circuit. 7 / 40 What is the wavelength of a 5 Hz wave that travels with a speed of 10 m/s ? 0.25 m 0.5 m 1 m 2 m 50 m From the equation λf = v, we find that 8 / 40 Two objects have the same mass and are located near each other at a distance (r). If the mass of one of the objects is doubled and the mass of the other object is tripled, what would be the change in gravitational attraction between them? Decrease by 1/6 Decrease by 2/3 Increase by 3/2 Increase by 5 Increase by 6 The correct answer is (E). The radius between the two masses does not change. That means in the gravitational equation the only thing that changes is the mass of the two bodies. Multiply them together to find the magnitude of the change in force they exert on each other. 9 / 40 A constant voltage power source is in a circuit where the resistance is increased by four. The voltage in the circuit increases by two. increases by four. decreases by two. decreases by four. remains the same. The correct answer is (E). A constant voltage source does not change, regardless of the value of the resistance added to the circuit. 10 / 40 A linear spring of force constant k is used in a physics lab experiment. A block of mass m is attached to the spring and the resulting frequency, f, of the simple harmonic oscillations is measured. Blocks of various masses are used in different trials, and in each case, the corresponding frequency is measured and recorded. If f2 is plotted versus 1/m, the graph will be a straight line with slope 4π2/k2 4π2/k 4π2k k/(4π2) k2/(4π2) The frequency of a spring-block simple harmonic oscillator is given by the equation . Squaring both sides of this equation, we get f2 = Therefore, if f2 is plotted versus (1/m), then the graph will be a straight line with slope . (Note: The slope of the line whose equation is y = ax is a.) 11 / 40 A tugboat pulls on an 84,000N barge with a cable having a breaking strength of 15,000N. The maximum acceleration the tugboat can apply to the barge without the cable breaking is .75 m/s2 1.0 m/s2 1.25 m/s2 1.5 m/s2 1.75 m/s2 The correct answer is (E). The maximum tension the cable can withstand is 15,000N.This is the limit to applied force. The barge weighs 84,000N, which is a mass of 8571 kg. Use F = ma to solve the problem. 12 / 40 The International Space Station is currently under construction. Eventually, simulated earth gravity may become a reality on the space station. What would the gravitational field through the central axis be like under these conditions? zero 0.25 g 0.5 g 0.75 g 1 g The correct answer is (A). The central axis would have a gravitational force of zero because there is no radial distance to provide a centripetal acceleration or centripetal force. 13 / 40 When a gas undergoes an adiabatic compression its temperature decreases. temperature increases. volume increases. pressure decreases. energy decreases. The correct answer is (B). As the gas undergoes air adiabatic compression, its temperature increases. 14 / 40 Two point charges are separated by a small distance. When the distance between the two particles is halved, which of the following descriptions is true? The particles attract one another. The particles repel one another. The particles exert the same force on one another. The particles exert twice as much force on one another. The particles exert four times as much force on one another. The correct answer is (E). The force the particles exert on one another increases as the inverse of the square of the distance between the two particles. 15 / 40 The choices below give a description of the quantities listed above. Match the statement below with the quantity it describes above. The number of wave crests passing a given point per unit of time. Frequency Amplitude Wavelength Velocity Period The correct answer is (A). The definition of the frequency of a wave is correctly stated in A 16 / 40 The three natural radiations, in order from most penetrating to least penetrating, are alpha, beta, and gamma. beta, gamma, and alpha. gamma, alpha, and beta. gamma, beta, and alpha. beta, alpha, and gamma. The correct answer is (D). The penetrating capability of radiation is based upon its energy. Gamma radiation is most energetic followed by beta then alpha. Q = (0.04 kg)(0.50 kJ/kg * degrees celsius)(50 degrees celsius − 20 degrees celsius)=0.6 kJ = 600 J 17 / 40 Tungsten-176 has a half-life of 2.5 hours. After how many hours will the disintegration rate of a tungsten-176 sample drop to its initial value? 5 8.3 10 12.5 25 After 3 half-lives, the activity will drop to (1/2)3 = 1/8 its initial value, and after 4 half-lives, it will drop to (1/2)4 = 1/16 its initial value. Since 1/10 is between 1/8 and 1/16, the time interval in this case is between 3 and 4 half-lives, that is, between 3(2.5 h) = 7.5 h and 4(2.5 h) = 10 h. Only B is in this range. 18 / 40 A train engine that weighs 5000N stops at the exact center of a bridge. The bridge weighs 75,000N and has two equally spaced pillars that completely support the bridge. The upward force exerted by each pillar 75,000N 40,000N 37,500N 2500N 0N The correct answer is (B). Each pillar supports exactly one-half of the weight of the train engine, which is 2,500N and is one-half the weight of the bridge. 19 / 40 A person standing 1.5 m in front of a plane flat mirror would see their image at a distance of .75 m 1.5 m 2.25 m 3 m 6 m The correct answer is (D). The image in a plane mirror appears as far into the mirror as the object is in front of the mirror.The image is 1.5 m into the mirror, and the object is 1.5 m in front of the mirror, which is a total of 3 m from the object. 20 / 40 A positively charged rod is brought near an uncharged pith ball that is being touched by a copper wire. Both the rod and the copper wire are simultaneously removed, and the pith ball is tested to find if any electrostatic charge is present. What is the result? The pith ball has been positively charged by conduction. The pith ball has been positively charged by induction. The pith ball has been negatively charged by conduction. The pith ball has been negatively charged by induction. The pith ball has not been charged in any way. The correct answer is (D). Objects that are touched by the charging body are charged by conduction. Objects that are not touched by the charging body are charged by induction. The negative charge is placed on the pith ball when a positively charged rod is brought near the pith ball. The pith ball is touched by a body other than the charging rod, which provides a path for electrons to flow onto the pith ball and charges the pith ball oppositely from the charge on the rod. 21 / 40 An object that is placed on the edge of a constant speed turntable has constant linear velocity. tangential acceleration. centripetal acceleration. centrifugal acceleration. no acceleration. The correct answer is (C). An object that is turning undergoes a change in direction. The change in direction is a change in velocity. A change in velocity through a period of time is acceleration. Because the acceleration is directed inward toward the center of rotation, this is a centripetal acceleration. 22 / 40 When can the instantaneous velocity of an object be equal to the average velocity of an object? It can never equal the average velocity. It can only equal the average velocity during acceleration. It can only equal the average velocity when the velocity is constant. It is always equal at the end of a displacement. They are equal at the end of a displacement The correct answer is (C). The only time the instantaneous velocity of an object equals the average velocity of an object is when the object moves with constant velocity. 23 / 40 A sphere of charge +Q is fixed in position. A smaller sphere of charge +q is placed near the larger sphere and released from rest. The small sphere will move away from the large sphere with decreasing velocity and decreasing acceleration. decreasing velocity and increasing acceleration. decreasing velocity and constant acceleration. increasing velocity and decreasing acceleration. increasing velocity and increasing acceleration. The acceleration of the small sphere is 24 / 40 The potential at point A in an electric field is 10V higher than at point B. If a negative charge, q = -2 C, is moved from point A to point B, then the potential energy of this charge will decrease by 20 J decrease by 5 J increase by 5 J increase by 20 J increase by 100 J 7 D As we move from point A to point B, the potential decreases by 10 V, so ∆V = -10 V. Now, since ∆U = q ∆ V, we have ∆U = (-2 C)(-10 V) = +20 J. 25 / 40 Compared to the parent nucleus, the daughter of a alpha decay has the same mass number but a greater atomic number the same mass number but a smaller atomic number a smaller mass number but the same atomic number a greater mass number but the same atomic number None of the above In alpha decay, a neutron is transformed into a proton and an electron. Therefore, the total nucleon number (mass number) doesn't change, but the number of protons (the atomic number) increases by one. 26 / 40 Two resistors, A and B, are in series in a circuit that carries a nonzero current. If the resistance of Resistor A is 4 times greater than the resistance of Resistor B, which of the following correctly compares the currents through these resistors (IA and IB, respectively) and the voltage drops across them (VA and VB, respectively)? IA = IB and VA = VB IA = IB and VA = 4VB IA = IB and VB = 4VA IA = 4IB and VA = 4VB IB = 4IA and VB = 4VA Resistors in series always share the same current, so we can eliminate D and E. Now, using Ohm's law, V = IR, we see that if I is constant, then V is proportional to R. Since RA = 4RB, we know that VA = 4VB. 27 / 40 An object of mass 2 kg has a linear momentum of magnitude 6 kg * m/s. What is this object's kinetic energy? 3 J 6 J 9 J 12 J 18 J The magnitude of the object's linear momentum is p = mv. If p = 6 kg * m/s and m = 2 kg, then v = 3 m/s. Therefore, the object's kinetic energy is K = mv2 = (2 kg)(3 m/s)2 = 9 J. 28 / 40 Which quantity can be expressed in the same units as impulse? Displacement Velocity Acceleration Linear momentum Kinetic energy Impulse is equal to force multiplied by time, so its units are N-s. Because 1 N = 1 kg-m/s2, we see that 1 N-s = 1 kg-m/s, which we immediately notice is the same as the units of mass (kg) times those of velocity (m/s), and mv is linear momentum, D. You may also have remembered the impulse-momentum theorem, which says that the impulse delivered to an object is equal to the resulting change in its linear momentum. Since impulse gives the change in linear momentum, it must be true that impulse can be expressed in the same units as linear momentum. 29 / 40 A parallel-plate capacitor is charged to a potential difference of ∆V; this results in a charge of +Q on one plate and a charge of -Q on the other. The capacitor is disconnected from the charging source, and a dielectric is then inserted. What happens to the potential difference and the stored electrical potential energy? The potential difference decreases, and the stored electrical potential energy decreases. The potential difference decreases, and the stored electrical potential energy increases. The potential difference increases, and the stored electrical potential energy decreases. The potential difference increases, and the stored electrical potential energy increases. The potential difference decreases, and the stored electrical potential energy remains unchanged. 8 A Since Q cannot change and C is increased (because of the dielectric), ∆V = Q/C must decrease. Also, since UE = , an increase in C with no change in Q implies a decrease in UE. FB = (0.04 C)(2e4 m/s)(0.5 T) = 400 N 30 / 40 A person standing on a horizontal floor feels two forces: the downward pull of gravity and the upward supporting force from the floor. These two forces have equal magnitudes and form an action/reaction pair have equal magnitudes but do not form an action/reaction pair have unequal magnitudes and form an action/reaction pair have unequal magnitudes and do not form an action/reaction pair None of the above Because the person is not accelerating, the net force he feels must be zero. Therefore, the magnitude of the upward normal force from the floor must balance that of the downward gravitational force. Although these two forces have equal magnitudes, they do not form an action/reaction pair because they both act on the same object (namely, the person). The forces in an action/reaction pair always act on different objects. 31 / 40 Which of the following best describes a perfectly inelastic collision free of external forces? Total linear momentum is never conserved. Total linear momentum is sometimes (but not always) conserved. Kinetic energy is never conserved. Kinetic energy is sometimes (but not always)conserved. Kinetic energy is always conserved. In a perfectly inelastic collision, kinetic energy is never conserved; some of the initial kinetic energy is always lost to heat and some is converted to potential energy in the deformed shapes of the objects as they lock together. 32 / 40 A force of 200 N is required to keep an object sliding at a constant speed of 2 m/s across a rough floor. How much power is being expended to maintain this motion? 50 W 100 W 200 W 400 W Cannot be determined from the information given Using the equation P = Fv, we find that P = (200 N)(2 m/s) = 400 W. 33 / 40 A charge of mass m and charge q is moving in a circle of radius r and speed v due to a uniform magnetic field B. If the speed is doubled to 2v, what happens to the period, T ? T increases by a factor of 2 T increases by a factor of 4 T stays the same T decreases by a factor of 2 T decreases by a factor of 4 The period T is the time it takes the charge to complete one revolution: T = Since the magnetic force is providing the centripetal force, Therefore, T = Since T is independent of v, it will remain unchanged. 34 / 40 Which type of decay ejects the heaviest particle? Alpha decay alpha decay delta V+ decay Electron capture Gamma decay When a nucleus undergoes alpha decay, it ejects an alpha particle, which is a helium-4 nucleus, composed of 2 protons and 2 neutrons. This is by far the heaviest decay particle that is ejected from a radioactive nucleus. 35 / 40 A bicyclist travels at a constant 25 km/hr for 30 minutes. He coasts for 15 minutes at a constant 20 km/hr and then pedals at a constant 40 km/hr for another 15 minutes. What was the average speed of the cyclist for the past hour? 22.5 km/hr 25 km/hr 27.5 km/hr 30 km/hr 32.5 km/hr The correct answer is (C). During the first 30 minutes (1/2 hour) the bicyclist travels 12.5 km. The next 15 minutes (1/4 hour) the bicyclist travels 5 km, and during the last 15 minutes the bicyclist travels another 10 km. The total distance the bicyclist traveled during one hour is the sum of the three distances, which are 12.5 km + 5 km + 10 km = 27.5 km 36 / 40 A superconductor is a device used to study the collisions of subatomic particles that have been accelerated to near light speeds a hollow, doughnut-shaped device containing a strong magnetic field for confinement of very high temperature plasmas an element used to generate high-energy coherent laser light an element whose supercooled vapor fills a cloud chamber to detect the tracks of charged particles when they initiate condensation of the vapor an element or alloy whose electrical resistivity vanishes when cooled to extremely low temperatures E is the definition of a superconductor. (A describes a particle accelerator/collider, and B describes a device known as a tokamak.) 37 / 40 A charged particle moving through a magnetic field will experience the largest force when moving with the field. moving against the field. moving at a 45 degrees angle to the field. moving at a 90 degrees angle to the field. the particle will not be affected. The correct answer is (D). The more magnetic field lines a charged particle crosses, the stronger the force exerted on the particle. Moving through the magnetic field in a perpendicular path (90 degrees) will cause the particle to cross the most field lines. 38 / 40 A train engine that weighs 5000N stops at the exact center of a bridge. The bridge weighs 75,000N and has two equally spaced pillars that completely support the bridge. The force exerted on the ground by a single pillar 75,000N 40,000N 37,500N 2500N 0N The correct answer is (B). The two equally spaced pillars each hold one half of the weight of the bridge. Each also supports one half of the weight of the train engine, which is located at the exact center of the bridge. 39 / 40 A stone is thrown horizontally with an initial speed of 30 m/s from a bridge. Find the stone's total speed when it enters the water 4 seconds later. (Ignore air resistance.) 30 m/s 40 m/s 50 m/s 60 m/s 70 m/s After 4 seconds, the stone's vertical speed has changed by ∆vy = ayt = (10 m/s2) (4 s) = 40 m/s. Since v0y = 0, the value of vy at t = 4 is 40 m/s. The horizontal speed does not change. Therefore, when the rock hits the water, its velocity has a horizontal component of 30 m/s and a vertical component of 40 m/s. 40 / 40 The choices below give a description of the quantities listed above. Match the statement below with the quantity it describes above. The distance between two points or two consecutive waves. Frequency Amplitude Wavelength Velocity Period The correct answer is (C). This is the correct definition for wavelength. 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