20 Created by Master Student Physics Practice Test #9 1 / 40 Of the following, which is the best description of the second law of thermodynamics? The total energy of the universe is a constant. The efficiency of a heat engine can never be greater than 50 percent. The amount of heat required to vaporize a liquid is greater than the amount of heat required to melt a solid of the same substance. The entropy of the universe is always increasing. As the altitude increases, the boiling point of water decreases. A is the first law of thermodynamics. C and E are true, but they are not equivalent to the second law of thermodynamics. B is false, but if it read, The efficiency of a heat engine can never be equal to 100 percent, then it would be equivalent to the Second Law. D is one of the several equivalent forms of the second law of thermodynamics. 2 / 40 The velocity of a particle of charge +4.0e-9 C and mass 2e-4 kg is perpendicular to a 0.1-tesla magnetic field. If the particle's speed is 3e4 m/s, what is the acceleration of this particle due to the magnetic force? 0.0006 m/s2 0.006 m/s2 0.06 m/s2 0.6 m/s2 None of the above The magnitude of the magnetic force is FB = qvB, so the acceleration of the particle has magnitude 3 / 40 The length of time a satellite takes to orbit the earth depends on its launch speed. mass. distance from the earth. weight. orbital direction. The correct answer is (C). The closer a satellite orbits the earth, the faster its period of rotation. The farther a satellite orbits from the earth, the longer its period of rotation. 4 / 40 Two similar pith balls are very near to one another, and each is charged with 2 excess electrons. The angle q between q1 and q2 is 5.5 degrees. One electron is removed from q1 and placed on q2 so that q1 has 1 electron and q2 has 3 electrons. The angle between the pith balls changes to 4 degrees. Which of the following statements is correct? I.The amount of electrostatic charge has decreased. II.The electrostatic force between the pith balls has decreased. III.Both the electrostatic charge and force have decreased. I only II only I and III only II and III only I, II, and III The correct answer is (B). The same number of charged bodies are still in the system, however, the redistribution of the charge has reduced the force the pith balls exert on one another. 5 / 40 Four resistors are hooked together in parallel. The resistors have values of 20, 40, 60, and 80 respectively. What is the total resistance of the resistors? 4.4 9.6 14.8 20 25.2 The correct answer is (B). The total resistance for a set of resistors in parallel is found by using the sum of the reciprocals. That is to do the following yielding the decimal solution Which is 6 / 40 A 30 kg child is standing in the back of a stationary 10 kg wagon that is free to move.The child jumps from the wagon into his mother's arms. Which of the following statements is correct at the moment he jumps from the wagon? The child's velocity is greater than the wagon's velocity. The wagon's velocity is greater than the child's velocity The impulse exerted by the child on the wagon is the same as the momentum gained by the wagon. The impulse exerted by the wagon on the child is larger than the momentum gained by the child. None of these statements is correct. The correct answer is (B). When the child jumps into his mother's arms, he pushes on the wagon as he jumps. The momentum the child gains when he jumps is passed on to the wagon, too. They both have the same momentum, but in opposite directions.The wagon must have a greater velocity since it has less mass. 7 / 40 A batter hits a long fly ball. Neglecting friction, which of the following statements is/are true? I. The time the ball is in free fall determines the horizontal distance it travels. II. The ball reaches its maximum velocity at the highest point of its flight. III. The upward velocity can never be greater than the horizontal velocity. I only II only I and III only II and III only I, II, and III The correct answer is (A). In this problem the object has both horizontal and vertical motion. The original velocity of the object can be of large magnitude on either the x axis or the y axis. It is absolutely true, however, that the object can only travel along the x (horizontal) axis as long as it is in free fall. 8 / 40 A baseball is thrown straight upward. What is the ball's acceleration at its highest point? g, downward g, downward g, upward g, upward The baseball is still under the influence of Earth's gravity. Its acceleration throughout the entire flight is constant, equal to g downward. 9 / 40 A 5 kg ball is swinging at the end of a 2 m string that has a tension of 6.25 N in it. Find the speed of the ball as it travels its circular path. 3.8N 4.4N 5N 5.6N 6.2N The correct answer is (C). The velocity of the ball in its pathway is calculated with the centripetal force equation, , which is rearranged to 10 / 40 At what point between a pair of charged parallel plates will the electric field be strongest? It is strongest between the plates. It is strongest near the positive plate. It is strongest near the negative plate. The field is constant between the plates. The field is variable, therefore the strong point also varies. The correct answer is (D). The electric field between two parallel plates is constant throughout. The value of the field is defined as E = F/q where E is the electric field, F is force, and q is charge. 11 / 40 What principle is the basis for the transmission of light through glass (fiber optic) cables, allowing the signal to be sent even if the cable is bent? Photoelectric effect Uncertainty principle Light diffraction Light polarization Total internal reflection Fiber optic cables transmit light using total internal reflection. A, B, C, and D do not apply here. 12 / 40 A dog walks 120 m due east before turning and running 45 m west. He then turns and trots 40 m due north. After completing his journey, he is 85 m northeast of his home. When he hears his master call him, he runs directly home. Which part of the trip is the longest vector? The eastward leg The westward leg The northward leg The distance from home The distance to home The correct answer is (A). The numerical value is the magnitude of the vector. The one with the largest numerical value is the longest vector. 13 / 40 The discrete spectral lines of line spectra occur when excitation of electrons takes place in solids. liquids. gases. plastics. all of these. The correct answer is (C). Gases provide electron sources that can be excited by the photons of light that strike them. 14 / 40 A 75 g ice cube is added to 450 g of boiling water. The water stops boiling immediately because: I. Heat is melting the ice. II. Condensation is occurring. III. Phase change occurs. I only II only I and III only II and III only I, II, and III The correct answer is (C). The heat in the water and any heat added to the water is used by the system to melt the ice. This constitutes a phase change, too. 15 / 40 If an object's speed is changing, which of the quantities could remain constant? Displacement Velocity Acceleration Linear momentum Kinetic energy If an object's speed is changing, it must be moving, so its displacement is changing. Since velocity, v, is speed plus direction, a change in speed automatically means a change in velocity. Now, since the velocity is changing, the linear momentum, p, must be changing also, since p = mv. Finally, because kinetic energy is equal to times the square of the speed, a changing speed implies a changing kinetic energy. The answer must be C. An object undergoing a change in speed may certainly be subject to a constant acceleration (gravitational acceleration, for example). 16 / 40 A transverse wave on a long horizontal rope with a wavelength of 8 m travels at 2 m/s. At t = 0, a particular point on the rope has a vertical displacement of +A, where A is the amplitude of the wave. At what time will the vertical displacement of this same point on the rope be -A ? t = s t = s t = s t = 2 s t = 4 s The time interval from a point moving from its maximum displacement above y = 0 (equilibrium) to its maximum displacement below equilibrium is equal to one-half the period of the wave. In this case 17 / 40 The acceleration due to gravity on the moon is 1/6 of its value on Earth. If an object weighs 20 N on the moon, what is its mass on Earth? 2 kg 7.2 kg 12 kg 60 kg 72 kg Since we know g = 10 m/s2 on the earth, the value of g on the moon must be (10) = m/s2. So, if an object weighs 20 N on the moon, its mass must be 18 / 40 When does an artificial earth satellite that is in an elliptical orbit experience its greatest centripetal acceleration? When it first enters orbit When it is nearest the earth When it is farthest from the earth When it leaves orbit Its centripetal acceleration is always the same The correct answer is (B). The satellite travels at essentially the same velocity in its orbit, although its speed does increase at its closest approach to the earth. The distance from the satellite to the earth also changes while the satellite orbits the earth. The closer approach to the earth decreases the radius of the orbit, which in turn causes an increase in the centripetal acceleration. 19 / 40 A block of aluminum and a block of iron each absorb the same amount of heat, and both blocks remain solid. The mass of the aluminum block is twice the mass of the iron block. If the specific heat of aluminum is twice the specific heat of iron, then the increase in temperature of the aluminum block is twice the increase in temperature of the iron block the increase in temperature of the aluminum block is four times the increase in temperature of the iron block the increase in temperature of the aluminum block is the same as increase in temperature of the iron block the increase in temperature of the iron block is twice the increase in temperature of the aluminum block the increase in temperature of the iron block is four times the increase in temperature of the aluminum block We use the equation q = mc(delta)T. Since both the aluminum block and the iron block absorb the same amount of heat, we have mAlcAl(delta)TAl = mFecFe(delta)TFe, where Al denotes aluminum and Fe denotes iron. Now, because mAl = 2mFe and cAl = 2cFe, we have 20 / 40 Sound waves cannot travel in air. metal. vacuum. water. wood. The correct answer is (C). Sound waves are compressional waves; thus they need a medium through which they can move. A vacuum does not provide a way for the compressions to move along. 21 / 40 An object is executing uniform circular motion. Which of the following quantities remain(s) constant during the object's motion? Velocity and acceleration Speed and velocity Speed and acceleration Acceleration only Speed only The velocity of an object undergoing uniform circular motion is always changing (because the direction is always changing), so A and B are eliminated. Furthermore, since the acceleration is centripetal, it must always point toward the center of the circle; so, as the object moves around the circle, the acceleration vector is also constantly changing direction. Since the acceleration changes, the answer must be E. Notice that for an object in uniform circular motion, both the velocity and the acceleration are changing because the directions of these vectors are always changing, even though their magnitudes stay the same. 22 / 40 A wooden crate is pushed across a concrete floor at 5 m/s and released. It slides to a stop after moving a short distance. The same crate is filled until it weighs twice as much as it did ly and again slid across the floor at 5 m/s and released. The stopping distance for the crate will be 1/4 as far. 1/2 as far. the same distance. twice as far. four times as far. The correct answer is (C). The coefficient of friction remains the same so the frictional force doubles, but the net force also doubles. Thus the crate is brought to a stop in the same distance. 23 / 40 A box of mass m slides down a frictionless inclined plane of length L and vertical height h. What is the change in its gravitational potential energy? -mgL -mgh -mgL/h -mgh/L -mghL Since the box (mass m) falls through a vertical distance of h, its gravitational potential energy decreases by mgh. The length of the ramp is irrelevant here. 24 / 40 The frequency of a wave is 4 cycles per second, and its speed is .08 meters per second. What is the period of one of the waves? .25 seconds .55 seconds 3.125 seconds .02 seconds 12.55 seconds The correct answer is (A). The period of a wave is the inverse of the frequency f = 1/T. 25 / 40 A clothesline is strung between two posts, and wet clothing weighing 200 N is hung on the line, which sags under the weight of the clothes. If one end of the line is pulled to straighten the line, which of the following would be true? I. The tension in the rope undergoes a large increase. II. The tension in the rope undergoes a large decrease. III. The weight in the rope undergoes a large increase. I only II only I and III only II and III only I, II, and III The correct answer is (A). The tension in the rope increases as the angle decreases because the sum of the four forces leads to ΣF = 2T = Wt/sinθ. Note that as the angle becomes smaller, its sine also becomes smaller. This causes the tension in the line to increase drastically. 26 / 40 Two batteries are hooked together in an 21. A hydrogen electron gains enough energy electric circuit. Which of the following to rise from the n=1 to the n=5 energy statements is/are true? level. How much energy does it gain? I. Maximum voltage is obtained when the batteries are wired in parallel. II. Maximum voltage is obtained when the batteries are wired in series. III. Maximum current capacity is obtained when the batteries are wired in parallel. I only II only I and III only II and III only I, II, and III The correct answer is (B). The voltage of the two batteries in series adds together, providing a voltage equivalent to their sum. 27 / 40 The impossibility of making simultaneous, arbitrarily precise measurements of the momentum and the position of an electron is accounted for in thermodynamics quantum mechanics classical electrodynamics special relativity general relativity Making simultaneous measurements of position and momentum is limited by the Uncertainty Principle, a quantum mechanical law. 28 / 40 An object at rest is placed into free fall at a height of20 m. What is the velocity of the object when the potential energy equals the kinetic energy? 8 m/s 11 m/s 14 m/s 17 m/s There is not enough information to determine the velocity. The correct answer is (C). The problem may be solved in several ways. Perhaps the best solution is a little thought. E.g., the potential energy and the kinetic energy are equal to each other when the object has fallen half the distance to the ground, or 10 m. We now treat it as a free fall problem by restating the situation a little. What is the velocity of an object that starts from rest and free falls a distance of 10 m? The solution is found by 29 / 40 Two disks of equal mass but different diameter are connected with an axle system that allows them to roll down an incline together. Both disks start and finish at the same time.Which of the following statements best describes the disks? Their tangential velocity is the same. Their tangential acceleration is the same. Their angular velocity is the same. Their angular displacement is the same. Their angular acceleration is the same. The correct answer is (A). Both disks move the same linear distance in the same time period. The smaller disk must make more revolutions to have the same tangential velocity as the large wheel. Since the number of revolutions for the small disk is larger, it also has a large angular acceleration. 30 / 40 Find the total capacitance for three capacitors in parallel with each other. The value of the capacitors is 10f, 15f and 35 f. 60 f 50 f 20 f 10 f 5 f The correct answer is (A). To find the capacitance for a group of capacitors in parallel with each other you add their capacitances together to find their sum. 10μf +15μf + 35μf = 60μf. 31 / 40 How much energy is dissipated as heat in 20 s by a 100 ohm resistor that carries a current of 0.5 A ? 50 J 100 J 250 J 500 J 1,000 J The equation P = I2R gives 32 / 40 Water drips from a leaky rainspout that is located at the top of a high building. The droplets of water fall at an interval of 1/2 second. As time passes, the distance between two consecutive drops of water decreases in a linear manner. increases in a linear manner. remains the same. decreases in a parabolic manner. increases in a parabolic manner. The correct answer is (B). Assume at t=0, first drop starts to fall. So, its distance from the rainspout, h1= 0.5 g t2 At t = 0.5 s, next drop starts to fall. So, its distance from the rainspout, h2= 0.5 g (t - 0.5)2 Separation between them at any time t = h1-h2 = 0.5 g [t2- (t - 0.5)2] = 0.25 g (2t - 0.5) So, it increases in a linear manner. 33 / 40 Two moving electrons enter a strong magnetic field at right angles to the field. The velocity of one of the electrons is four times greater then the velocity of the other electron. Which of the following best describes the ration of the circular radii the two electrons follow? The faster electron has a radius two times larger than the slower electron. The faster electron has a radius four times larger than the slower electron. The faster electron has a radius eight times larger than the slower electron. The faster electron has a radius sixteen times larger than the slower electron. The faster electron has a radius sixty-four times larger than the slower electron. The correct answer is (B). The radius of the curved path the electron follows in the magnetic field is r=mv/Bq. Both particles are electrons, which have the same mass, and the force exerted by the magnetic field remains the same, so the only difference is the velocity. The ratio of the velocity of the fast electron compared to the slow electron is 4:1.The fast electron has a radius 4 times larger than the slow electron. 34 / 40 An object moves at constant speed in a circular path. True statements about the motion include which of the following? I. The velocity is constant. II. The acceleration is constant. III. The net force on the object is zero since its speed is constant. I and II only None of the above II only I and III only II and III only Neither the velocity nor the acceleration is constant because the direction of each of these vectors is always changing as the object moves along its circular path. And the net force on the object is not zero because a centripetal force must be acting to provide the necessary centripetal acceleration to maintain the object's circular motion. 35 / 40 A motorcycle racer starts from rest and accelerates on a straight track at 5 m/s2. How far does the racer travel in 8 seconds? 40 m 60 m 80 m 120 m 160 m The correct answer is (E). The displacement of the motorcycle rider is found with . 36 / 40 A pair of point charges, which have charges of -3 micro coulombs and -4 micro coulombs, is separated by 2 cm. What is the value of the force between them? 600N 300N 540N 270N 400N The correct answer is (D). Coulombs Law is 37 / 40 For question above, what is the magnitude of the acceleration of the pile driver while it drives the nail into the board? -165 m/s2 -800 m/s2 -1600 m/s2 -2000 m/s2 -3200 m/s2 The correct answer is (B). The velocity of the pile driver at the time it first contacts the head of the nail is . Since, by conservation of energy, . V is also the original velocity as the nail is driven into the wood for a distance of .0245m. Stating the equations: 38 / 40 A charge of -3Q is transferred to a solid metal sphere of radius r. Where will this excess charge reside? -Q at the center, and -2Q on the outer surface -2Q at the center, and -Q on the outer surface -3Q at the center -3Q on the outer surface -Q at the center, -Q in a ring of radius r, and -Q on the outer surface All excess electric charge on a conductor resides on the outer surface. 39 / 40 A frictionless inclined plane of length 20 m has a maximum vertical height of 5 m. If an object of mass 2 kg is placed on the plane, which of the following best approximates the net force it feels? 5 N 10 N 15 N 20 N 30 N The net force that the object feels on the inclined plane is mg sinθ, the component of the gravitational force that is parallel to the ramp. Since sin θ = (5 m)/(20 m) = 1/4, we have Fnet = (2 kg)(10 N/kg)() = 5 N. 40 / 40 Two gases are insulated from their surroundings but are in contact with each other so heat can flow between them. One gas is hot at t = 0 and the other gas is cold at t = 0. After time passes and the gases equilibrate, which of the following will have happened? The particles in the cold gas will have slowed in their rate of movement. The particles in the hot gas will have increased their rate of movement. The temperature of the cold gas will have decreased. The temperature of the hot gas will have increased. The temperature of the hot gas will have decreased. The correct answer is (E). The hot gas, which is in contact with the cold gas, will lose heat to the cold gas. The transfer of heat is always from the hot object to the cold object, unless work is done on the system. Your score is The average score is 38% LinkedIn Facebook Twitter VKontakte 0% Restart quiz Previous Quiz Next Quiz
