18 Created by Master Student Physics Practice Test #6 1 / 40 A light ray that enters a glass block from the air is refracted because the light travels faster in the glass than in the air. the light travels slower in the glass than in the air. the light waves invert as they enter the glass. the light waves increase their amplitudes in the glass. the light intensity is greater in the glass than in the air. The correct answer is (B). When a light ray enters an optically denser material, it bends toward the normal because the light slows down in the material. 2 / 40 When a skydiver jumps from an airplane, he eventually reaches terminal velocity. At that time the force of the air resistance is equal to his mass. equal to twice his mass. equal to his weight. equal to twice his weight. equal to 1/2 his weight. The correct answer is (C). The skydiver accelerates after he jumps until the friction from the air is equal to his downward force, which is his weight. 3 / 40 Any object that is accelerated to near the speed of light experiences which of the following? An increase in its length An increase in the rate of time passage Decrease in energy Decrease in momentum Increase in mass The correct answer is (E). All the answers are stated opposite from their correct relativistic statement except for choice (E). 4 / 40 A professional golfer strikes a golf ball with his driver, imparting a momentum of 8 kg·m/s on the ball. The golf ball strikes a wall and maintains contact for .0025 seconds before it bounces straight backward at the same velocity with which it struck the wall. The momentum of the golf ball is 6400 kg·m/s 3200 kg.·m/s 8 kg·m/s .02 kg·m/s .01 kg·m/s The correct answer is (C). The collision described in the problem is perfectly elastic because the golf ball had the same velocity when it rebounded from the wall as when it struck the wall. Momentum is conserved perfectly, so the golf ball must have the same momentum after the collision with the wall as it had when it approached the wall before the collision. 5 / 40 A person standing in an elevator watches a spider hanging from a thread attached to the ceiling. Suddenly the elevator accelerates downward. The person watching the spider on the thread will see the spider thread snap and the spider slowly fall. the spider thread and spider float upward. the spider thread snap and the spider slowly float upward. the spider thread and the spider remain as they were before the acceleration began. the spider thread begin to swing back and forth like a pendulum. The correct answer is (D). The acceleration affects the spider in the same way that it affects the observer. If the elevator were in free fall, everything in the elevator would free fall together, including the spider. If the elevator accelerates upward, the spider experiences an apparent gain in weight, just as a person riding in the elevator does. 6 / 40 Two separate 10L containers each contain a different gas. One gas is at a temperature of 400K; the other gas is at a temperature of 200K. When both gases are added to the same 10L container, which statement is correct? I. The hotter gas loses heat to the cooler gas. II. The hotter gas increases in temperature when the two are squeezed together. III. The cooler gas decreases in temperature when placed into the second container. I only II only I and III only II and III only I, II, and III The correct answer is (A). The first law of thermodynamics makes it clear that a hot object loses heat to a cold object. If no heat is added or subtracted from a system, the heat in the system remains constant in the system. 7 / 40 A transformer contains 4000 turns on its primary side and 500 turns on the secondary side. If the input voltage is 240 V, calculate the voltage output of the secondary side. 15 V 30 V 60 V 120 V 240 V The correct answer is (B). The transformer equation is 8 / 40 A force F of strength 20 N acts on an object of mass 3 kg as it moves a distance of 4 m. If F is perpendicular to the 4 m displacement, the work it does is equal to 0 J 60 J 80 J 600 J 2,400 J Since the force F is perpendicular to the displacement, the work it does is zero. 9 / 40 An unknown particle is being studied in a magnetic field of variable intensity and direction. When the magnetic field is turned off, the particle is observed to move toward the earth. When the magnetic field is turned on, the particle is observed to continue to move toward the earth, no matter the strength or the direction of the magnetic field. Which of the particles listed below is most likely the unknown particle? Beta particle Alpha particle Positron Neutron Gamma ray The correct answer is (D). The particle is completely unaffected by the field, which eliminates the charge-carrying particles. Thus the electron, the positron (a positive electron), and the proton are not the correct choice. The gamma ray is also unaffected by a magnetic field, but it is not a particle and would not be seen, so it, too, is eliminated from consideration. The only particle that is unaffected by the magnetic field is the neutron. 10 / 40 A girl standing on a high bridge over a creek throws a rock straight down at leaves floating in the creek. Just as she throws the rock she accidentally drops another rock. Neglecting air resistance, which statement best describes the situation just as the rocks reach the water? The acceleration of the thrown rock is greater. The acceleration of the dropped rock is greater. The acceleration of both rocks is the same. The average velocity of both rocks is the same. The final velocity of both rocks is the same. The correct answer is (C). The starting velocity of the two rocks is not the same, but once in free fall the acceleration of the two rocks is equal. 11 / 40 While anchored at sea, a captain notices the wave peaks are separated by 16 m and occur at a rate of 1 wave every 2 seconds. What is the velocity of these waves? 4 m/s 8 m/s 16 m/s 32 m/s 64 m/s The correct answer is (B). The velocity of a wave is v = λ·f. Substitute into the equation and solve. v = λf = (0.5 m)(6.0 Hz) = 3.0 m/s 12 / 40 An empty soda can with a few ml of water inside is heated to steaming and quickly inverted into an ice water bath. The can is instantly crushed because energy in the can is lost. water vapor condenses leaving a vacuum, which sucks the can in. water vapor condenses and outside air pressure crushes the can. the cold water shrinks the hot can. water pressure in the ice bath crushes the can The correct answer is (C). The water vapor in the can is hot and at atmospheric pressure. Cooling the can quickly condenses the water vapor, which also reduces the pressure inside the can. The outside atmospheric pressure is greater, thus crushing the can. 13 / 40 A professional golfer drives a golf ball 230 meters down the fairway. When the club head strikes the golf ball the impact force on the golf ball is greatest the impact force on the club head is greatest the impact force is the same for both. the impact force has no effect on the club the impact force has no effect on the ball The correct answer is (C). The contact between the golf club and the ball constitutes an equal and opposite force pair. 14 / 40 During a company picnic, 6 accounting department workers participate in a tug of war with 6 sales force personnel. Each team pulls on the rope with 1200N of force. What is the tension in the rope? 2400N 1200N 600N 200N 100N The correct answer is (B). The tension in a rope is the same throughout. Both teams must pull with a force of 1200N to maintain static equilibrium, so the total tension is 2400N. 15 / 40 Which of the following equations best states the relationship between a material's coefficient of volume expansion due to heating, delta V, and its coefficient of linear expansion, delta L? delta V = delta L delta V = 3delta L delta V = delta L + delta L2 delta V = delta L3 delta V = 3delta L3 Since the coefficient of thermal expansion has units of deg−1 whether it's for linear, area, or volume expansion, we can eliminate C, D, and E, because the units of delta V would be wrong if any of these equations were true. Now, all you need to remember is that the coefficient of volume expansion is different from the coefficient of linear expansion to eliminate A and choose B. [In case you want to see how B is derived, notice that since each linear dimension, L, of a solid increases by delta LL(delta)T, the new volume of a heated solid, V ², is V(1 + delta L(delta)T)3 = V(1 + 3delta L(delta)T + 3delta L2(delta)T + delta L3(delta)T). Since delta L is so small, the terms involving delta L2 and delta L3 are really small and can be i 16 / 40 Which of the following changes to a double-slit interference experiment with light would increase the widths of the fringes in the diffraction pattern that appears on the screen? Use light of a shorter wavelength Move the screen closer to the slits Move the slits closer together Use light with a lower wave speed Increase the intensity of the light Relative to the central maximum, the locations of the bright fringes on the screen are given by the expression mL(λ/d), where λ is the wavelength of the light used, L is the distance to the screen, d is the separation of the slits, and m is an integer. The width of a fringe is, therefore (m + 1)L(λ/d) - mL(λ/d) = λL/d. One way to increase λL/d is to decrease d. 17 / 40 A 750N person stands on a scale while holding a briefcase inside a freely falling elevator. Which of the following is true? If the briefcase were released it would rise to the ceiling. The person's acceleration is zero. The person's attraction toward the earth is zero. The person's apparent weight is zero. If the briefcase were released it would fall to the floor. The correct answer is (D). The apparent weight is zero. The person is in free fall. No forces are acting on the person except gravity. 18 / 40 Which of the following best describes the electric field about a positive point charge? The field strengthens as the distance from the point charge increases. The field is a constant throughout space. The field weakens as the distance from the point change increases. The field is oriented toward the point charge. The field cannot be determined. The correct answer is (C). The value of the electric field about a point source is E =kq/r2 . The distance from the point in question determines the strength of the electric field in this case. 19 / 40 Which of the following best approximates the energy of a photon whose wavelength is 2.0 nm? (Planck's constant, h, has a value of 6.6e-34 J * s.) 4e-51 J 1e-34 J 1e-16 J 1e34 J 2e-50 J Combining the equation E = hf with f = c/ λ gives us (2mFe)(2cFe)(delta)TAl = mFecFe(delta)TFe ⇒ 4(delta)TAl = (delta)TFe 20 / 40 A child is swinging on a swing set. As the child reaches the lowest point in her swing the tension in the rope is equal to her weight. the tension in the rope supplies a centrifugal force. her kinetic energy is at maximum. her tangential acceleration equals gravity. her angular velocity is minimum. The correct answer is (C). All the gravitational potential energy at the top of the child's swing pathway is converted into kinetic energy at the bottom of her swing pathway. 21 / 40 Astronomers can tell whether a star is approaching or receding from the earth by the absorption spectra of the star. Doppler shift of the starlight. temperature of the star. brightness of the starlight. thermal signature of the star. The correct answer is (B). Stars are a source of light waves. As such, the waves approach the earth as fronts. When a star is approaching the earth the wave fronts reach us at an increasing rate. When a star is receding from us, the wave fronts reach us at a lower rate. In both cases a frequency change (Doppler shift) can be detected. 22 / 40 A 750 g peregrine falcon dives straight down towards a 400 g pigeon, which is flying level to the ground. Just before the falcon makes impact its velocity is 35 m/s. The velocity of the falcon and the pigeon in its talons immediately after impact is most nearly 35 m/s 31.95 m/s 28.9 m/s 25.85 m/s 22.8 m/s The correct answer is (E). Use conservation of momentum for the problem. 23 / 40 The specific heat for substance A is twice the specific heat of substance B. The same mass of each substance is allowed to gain 50 Joules of heat energy. As a result of the heating process the temperature of A rises twice as much as B. the temperature of A rises four times as much as B. the temperature of B rises twice as much as A. the temperature of B rises four times as much as A. the temperature of both B and A rise the same amount. The correct answer is (C). The specific heat capacity of a substance is defined as the amount of heat required to raise l g of the substance by 1 degrees celsius. If substance A has a specific heat capacity that is twice the specific heat capacity of substance B, that means twice as much heat is required to raise the temperature of substance A as is required for substance B. The converse is also true ”the heat required to raise the temperature of substance A by 1 degrees celsius will raise the temperature of substance B by 2 degrees celsius. 24 / 40 As the air around the base of a candle flame is heated, it rises and is replaced by cooler air. This illustrates what type of heat transfer? Conduction Convection Radiation Diffraction Latent heat The transfer of heat due to a moving fluid (such as air) is known as convection. (D and E, by the way, are not modes of heat transfer and can therefore be eliminated immediately.) 25 / 40 A gamma ray is emitted from the nucleus of an unstable atom. What is the result? The number of electrons decreases. The number of electrons increases. The mass of the nucleus increases. The mass of the nucleus decreases. The mass of the nucleus remains the same. The correct answer is (E). Gamma radiation has no mass. It is emitted from an unstable nucleus, which changes to a lower energy state. There is no mass change involved, so the nucleus remains essentially the same minus the emitted energy. 26 / 40 Three ice cubes are placed into three equal beakers filled with water. One ice cube has a mass of 50 g, the second ice cube has a mass of 75 g, and the third ice cube has a mass of 100 g. After the ice cubes are added, each beaker is filled to the brim with water at a temperature of 1 degrees celsius. After a period of time passes and all three ice cubes melt, which of the following situations is most likely? All three beakers have overflowed. None of the beakers have overflowed. The beaker with the 100 g ice cube has overflowed. The beakers with the 100 g and the 75 g ice cube in them have overflowed. The beaker with the 50 g ice cube has overflowed. The correct answer is (B). When water freezes, it becomes less dense. Therefore, when ice cubes are placed into liquid water, they displace a volume of water equal to their weight. When the ice melts no further, volume is added to the container. 27 / 40 If the distance between two positive point charges is tripled, then the strength of the electrostatic repulsion between them will decrease by a factor of 3 6 8 9 12 Electrostatic force obeys an inverse-square law: FE ∠. Therefore, if r increases by a factor of 3, then FE decreases by a factor of 32 = 9. 28 / 40 The image created by a converging lens is projected onto a screen that's 60 cm from the lens. If the height of the image is the height of the object, what's the focal length of the lens? 36 cm 45 cm 48 cm 72 cm 80 cm Since the image is projected onto a screen, it must be real, and therefore inverted. The magnification must be negative, so 29 / 40 Two charged objects are moved 50% closer to one another. Which statement about the electric force between the objects is true? The force between them doubles. The force between them halves. The force between them remains the same. The force between them reverses. The force between them operates in the same direction. The correct answer is (E). The charge on the two does not change, so the force between them MUST operate in the same direction. The magnitude of the force increases by 4. 30 / 40 Which phenomenon is NOT experienced by sound waves? Reflection Refraction Polarization Diffraction Interference Only a transverse wave, defined to be a wave in which the oscillation is perpendicular to the direction of wave propagation, can be polarized. Since sound waves are longitudinal, they cannot be polarized. 31 / 40 A solid copper sphere has a charge of .2C placed on it. Which of the following statements best describes the charge distribution for the sphere? The charge is equally distributed throughout the entire sphere. The charge is concentrated inside the sphere with some charge on the outside. The charge is equally distributed on the outside surface of the sphere. The charge is equally distributed throughout the inside of the sphere only. The charge is concentrated in the center of the sphere. The correct answer is (C). The charge on a solid conducting body is found on the outside of the object. The charges distribute themselves equally around the outside of the conducting body because of the mutual repulsion the excess charges have for themselves. 32 / 40 A pendulum has a 1 second period of vibration. At what period in time would the string have to break for the pendulum bob to fly away the maximum possible distance from, but not below, the rest position of the pendulum bob? (The zero point for the pendulum at t = 0 is at the maximum displacement) t = .125 sec t = .25 sec t = .375 sec t = .5 sec t = .625 sec The correct answer is (C). When the time equals .375 seconds, the pendulum is 3/4 of the way through the first half of its period. At that time, if the pendulum string breaks, the pendulum will fly off at a 45 degrees angle, which is the angle that gives the pendulum bob maximum time of flight. 33 / 40 An ideal gas is placed in a 4L container at a temperature of 300K and a pressure of 6 atmospheres. The pressure is held constant while the volume of the gas is halved. What is the new temperature of the gas? 1200K 600K 300K 150K 75K The correct answer is (D). The ideal gas law equation 34 / 40 A student is performing a lab experiment on simple harmonic motion. She has two different springs (with force constants k1 and k2) and two different blocks (of masses m1 and m2). If k1 = 2k2 and m1 = 2m2, which of the following combinations would give the student the spring-block simple harmonic oscillator with the shortest period? The spring with force constant k1 and the block of mass m1 The spring with force constant k1 and the block of mass m2 The spring with force constant k2 and the block of mass m1 The spring with force constant k2 and the block of mass m2 All the combinations above would give the same period. The period of the spring-block simple harmonic oscillator is given by the equation T = . So, to make T as small as possible, we want m to be as small as possible and k to be as large as possible. Since m2 is the smaller mass and k1 is the larger spring constant, this combination will give the oscillator the shortest period. 35 / 40 A force of 53N is applied to a 176.4N object that is at rest. A frictional force of 8N must be overcome to move the object. What is the acceleration of the object? .3 m/s2 2.5 m/s2 2.9 m/s2 4.24 m/s2 6.625 m/s2 The correct answer is (B). Use F=ma to solve the problem. Don't forget to subtract the frictional force from the applied force. Also don't forget to convert the weight of the object into mass. Set the problem up in this manner: 36 / 40 While riding on a merry-go-round, you decide to move from a position close to the center to a position on the outside rim of the merry-go-round. After you have changed position, which of the following has remained the same? Tangential acceleration Centripetal force Angular displacement Tangential velocity Tangential displacement The correct answer is (C). Regardless of where on the merrygo- round you are located during the ride, your angular displacement is the same for the whole ride. 37 / 40 A hydrogen electron gains enough energy to rise from the n=1 to the n=5 energy level. How much energy does it gain? +.88 eV +2.54 eV +10.21 eV +12.09 eV +12.75 eV The correct answer is (E). The hydrogen must gain 12.75eV of energy to be raised to the n = 5 level, where its potential is .85eV. 38 / 40 An object of mass m is traveling at constant speed v in a circular path of radius r. How much work is done by the centripetal force during one half of a revolution? Ï€mv2 2Ï€mv2 0 Ï€mv2r 2Ï€mv2r Since the centripetal force always points along a radius toward the center of the circle, and the velocity of the object is always tangent to the circle (and thus perpendicular to the radius), the work done by the centripetal force is zero. Alternatively, since the object's speed remains constant, the work-energy theorem tells us that no work is being performed. 39 / 40 Two people, one of mass 100 kg and the other of mass 50 kg, stand facing each other on an ice-covered (essentially frictionless) pond. If the heavier person pushes on the lighter one with a force F, then the force felt by the heavier person is -F the force felt by the heavier person is -2F the magnitude of the acceleration of the lighter person will be of the magnitude of the acceleration of the heavier person the magnitude of the acceleration of the lighter person will be twice the magnitude of the acceleration of the heavier person None of the above By Newton's third law, the force on the heavier person is equal but opposite to the force on the lighter person, eliminating A and B. Since the lighter person has the mass of the heavier person and acceleration is inversely proportional to mass, the magnitude of the lighter person's acceleration will be twice that of the heavier person. 40 / 40 A pile of 11 books weighing 2 N each is sitting on a table. With what total force does the table push back on the books? 2N 11N 22N 33N 44N The correct answer is (C). This is an example of the first condition of equilibrium. 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