134 Created by Master Student Physics Practice Test #1 1 / 40 A ball of mass m traveling horizontally with velocity v strikes a massive vertical wall and rebounds back along its original direction with no change in speed. What is the magnitude of the impulse delivered by the wall to the ball? mv mv 2mv 4mv The impulse delivered to the ball is equal to its change in momentum. The momentum of the ball was mv before hitting the wall and m(-v) after. Therefore, the change in momentum is m(-v) - mv = -2mv, so the magnitude of the momentum change (and the impulse) is 2mv. 2 / 40 What's the missing particle in the following nuclear reaction? Proton Neutron Electron Positron Deuteron In order to balance the mass number (the superscripts), we must have 2 + 63 = 64 + A, so A = 1. In order to balance the charge (the subscripts), we need 1 + 29 = 30 + Z, so Z = 0. A particle with a mass number of 1 and no charge is a neutron, . 3 / 40 Electromagnetic induction occurs in a wire when a change occurs in the current in the wire. intensity of the electric field of the wire. voltage applied to the wire. magnetic field intensity applied to the wire. resistance is added to the wire. The correct answer is (D). Current is induced into a wire when the wire is placed in a changing magnetic field because of the moving line of flux crossing the wire. This is one of the ways a current is magnetically induced into a wire. 4 / 40 A ball of mass 0.5 kg, initially at rest, acquires a speed of 4 m/s immediately after being kicked by a force of strength 20 N. For how long did this force act on the ball? 0.01 s 0.02 s 0.1 s 0.2 s 1 s The impulse delivered to the ball, J = Fâˆ†t, equals its change in momentum. Since the ball started from rest, we have 5 / 40 In the theory of relativity it is stated that all laws of nature are the same in reference frames that accelerate. vibrate. rotate. oscillate. move at a constant rate. The correct answer is (E). This is Einstein's statement concerning the relationship between the natural laws of physics and frames of reference. All physical laws are the same for systems that are moving at constant rate. 6 / 40 Einstein's theory of relativity is based on which of the following statements? Mass and energy are equivalent. The velocity of light is a constant. Space and time are anomalies. All particles have antiparticles. Energy is infinite. The correct answer is (B). One of the basic postulates in Einstein's Theory of Relativity is the speed of light, which is constant for everyone. 7 / 40 A spaceship is moving directly toward a planet at a speed of . When the spaceship is 4.5e8 m from the planet (as measured by someone on the spaceship), a pulse of light is emitted by someone on the planet. As measured by someone on the spaceship, how long does it take the light pulse to travel from the planet to the ship? 0.5 sec 1.0 sec 1.5 sec 2.0 sec 2.5 sec The second postulate of Einstein's theory of special relativity states that the speed of light is a universal constant (c = 3e8 m/s), regardless of the motion of the source or the detector. So despite the fact that the spaceship is approaching the planet at a speed of c/2, occupants of the ship will still measure the speed of light to be c. The time it takes the light pulse to travel a distance of 4.5e8 m is 8 / 40 An object of mass 2 kg increases in speed from 2 m/s to 4 m/s in 3 s. What was the total work performed on the object during this time interval? 4 J 6 J 12 J 24 J 36 J Use the work-energy theorem. 4 resistors in series = 24ohm 3 resistors in parallel together with one resistor in series with the parallel resistors = 8ohm 2 resistors in parallel together that are in series with 2 more resistors that are in parallel together = 6ohm 9 / 40 When U-235 is fissioned in a nuclear reactor, the nuclear reaction is maintained by heat produced in the reactor. the moderator rods. radioactive decay products. vibrations induced in the U-235. neutrons produced in the reaction. The correct answer is (E). A chain reaction (industrial fission is a chain reaction) continues because of the neutrons that are emitted in the fissioning of each U-235 atom. 10 / 40 When a projectile moving in a parabolic path reaches its highest point above the ground, its velocity is instantaneously zero its acceleration is instantaneously zero its weight balances the force of air resistance the net force it feels is instantaneously zero None of the above When a projectile moving in a parabolic path reaches the top of its path, its vertical velocity is instantaneously zero. A is a trap; it is wrong because the projectile has a (constant) horizontal velocity during its entire flight. B and D are equivalent, so both can be eliminated. C can also be eliminated; the weight of the projectile points downward, and when the projectile is at the top of its path and has a purely horizontal velocity, the force of air resistance is also horizontal. There is no reason why the vertical force must have the same magnitude as the horizontal force. The answer must be E. 11 / 40 Two different light bulbs are in a DC circuit powered by an 18 V battery as its power source. The two bulbs are rated at 4.5 watts (B1) and 6.75 watts (B2) each. What are the resistances of the two light bulbs (B1) and (B2)? B1 is 48 ohm, and B2 is 72 ohm. B1 is 72 ohm, and B2 is 48 ohm. B1 is 2.67 ohm, and B2 is 4 ohm. B1 is 4 ohm, and B2 is 2.67 ohm. B1 is 20.25 ohm, and B2 is 45.56 ohm. The correct answer is (B). The resistance is calculated by using the power equation, R = V2/P. The solutions are: 12 / 40 While a child flies a kite on a breezy day, a burst of wind causes the kite to fly in 1.6 m diameter circles in the sky every second. If the circular motion were converted to a straight down speed, how fast would the kite dive toward the ground? 3.14 m/s 5 m/s 6.28 m/s 9.8 m/s 15.7 m/s The correct answer is (B). The kite rotates around a 5 m circumference in 1 second (C = 2 Ï€r). Although the path of the kite is circular, it travels 5 m every second. The velocity is v =5m/1s=5m/s. 13 / 40 A 20 N block is being pushed across a horizontal table by an 18 N force. If the coefficient of kinetic friction between the block and the table is 0.4, find the acceleration of the block. 0.5 m/s2 1 m/s2 5 m/s2 7.5 m/s2 9 m/s2 The net force on the block is F - Ff = F - Î¼kFN = F -Î¼kFw = (18 N) - (0.4)(20 N) = 10 N. Since Fnet = ma = ()a, we find that 10 N = []a, which gives a = 5 m/s2. 14 / 40 Electrical energy is changed into mechanical energy in a device called a/an electromagnet. generator. magnetron. motor. transformer. The correct answer is (D). An electric current is passed through an electromagnet or rotor, which causes it to spin within an applied magnetic field. The spinning rotor is the source of mechanical energy that is derived from electrical energy. 15 / 40 The time it takes a satellite to make one orbit around the earth depends on the satellite's acceleration. weight. direction of rotation. distance from earth. launch speed. The correct answer is (D). The centripetal force required to keep a satellite in orbit remains constant. That means the closer to earth a satellite is, the faster it must travel in its orbit Fc = mV2/r . The farther the satellite is located from the earth, the slower it travels in orbit. 16 / 40 When a photon strikes an electron and energizes it, the electron will receive the most energy from the photon if the electron does not spin when it is struck. the photon has a high velocity. the photon has a low velocity. the photon has a long wavelength. the photon has a high frequency. The correct answer is (E). The higher the frequency of a photon, the more energy it has, therefore the more energy it can impart to the electron. 17 / 40 Which of the following statements is true? Electric field vectors point toward a positive source charge, and the resulting electric force on an electron would point in the same direction as the electric field vector. Electric field vectors point toward a positive source charge, and the resulting electric force on an electron would point in the opposite direction from the electric field vector. Electric field vectors point toward a negative source charge, and the resulting electric force on an electron would point in the same direction as the electric field vector. Electric field vectors point toward a negative source charge, and the resulting electric force on an electron would point in the opposite direction from the electric field vector. None of the above By definition, electric field vectors point away from a positive source charge and toward a negative source charge. Furthermore, since an electron (which is negatively charged) would be repelled from a negative source charge, the resulting electric force on an electron would point away from a negative source charge, in the opposite direction from the electric field vector. 18 / 40 An object falls with constant acceleration near the earth. Which statement best describes the velocity of the object? The velocity is constant. The velocity is decreasing. The velocity constantly changes in proportion to its weight. The velocity is not related to its acceleration. The velocity changes by the same amount each second. The correct answer is (E). Look at the graph of velocity. It is a straight line. The velocity increases by the same amount each second, additional proof that V = at. 19 / 40 What is the wavelength of an X-ray whose frequency is 1.0e18 Hz? 3.3e-11 m 3.0e-10 m 3.3e-9 m 3.0e-8 m 3.0e26 m From the equation Î»f = c, we find that 20 / 40 If a 60-watt lightbulb operates at a voltage of 120 V, what is the resistance of the bulb? 2ohm 30ohm 240ohm 720ohm 7,200ohm Use the equation P = . 21 / 40 Which wave characteristic describes the number of wave crests passing a given point per unit time? Frequency Amplitude Wavelength Velocity Period The correct answer is (A). The definition of the frequency of a wave system is the number of waves per unit time, which is the same as saying the number of crests that pass a given point over a given time. 22 / 40 Ice, which has a temperature of 0 degrees celsius, is added to 500 g of water that has a temperature of 100 degrees celsius. Ice is continually added to the system until it has all melted and no more ice will melt. What is the temperature of the water in the system? 50 degrees celsius 25 degrees celsius 4.184 degrees celsius 1 degrees celsius 0 degrees celsius The correct answer is (E). The phase change to melt the ice drains all the heat from the water. At 0 degrees celsius ice will no longer melt because all the heat has been removed from the water. 23 / 40 An Olympic weight lifter lifts a weight bar weighing 2000N straight up to a height of 2.25 m in a time of .65 seconds. The weight lifter stands holding the weight at that height for the next 4 seconds before dropping the weights to the floor. How much work did the weight lifter do while holding the weights overhead? 1300 Joules 3077 Joules 4500 Joules 8000 Joules No work was done The correct answer is (E). Work is defined as a force applied through a distance. The weight lifter did not move the weights through any distance after he lifted them overhead. He just stood holding the weights overhead, which does not meet the meaning of work in a physics sense. 24 / 40 A goldfish swims through an aquarium by moving its fins and tail. What causes the fish to move forward? I. The force the water exerts on the goldfish II. The force the tail of the goldfish exerts on the water III. The force the fins of the goldfish exert on the water. I only II only I and III only II and III only I, II, and III The correct answer is (E). The goldfish is pushed along by the water as a part of the action-reaction force pair as stated in Newton's Third Law. 25 / 40 A dog walks 120 m due east, then turns and runs 60 m west. An interesting smell attracts the dog, and it trots 40 m due north. At this point the dog is 85 m northeast of his home. The dog hears his master call him and he runs directly home. Which part of the trip is the largest vector? The eastward leg The westward leg The northward leg The distance from home The distance to home The correct answer is (A). The longest leg the dog walked is the eastward vector. The fact that some of the length of the vector was later cancelled when the dog walked in the opposite direction does not change the length of the individual vector. 26 / 40 A heat engine receives 150 Joules of heat energy and performs 70 Joules of work. If heat cannot be removed from the heat engine in any other way, by what value does the internal energy of the system change? 0 J 40 J 80 J 120 J 150 J The correct answer is (C). The first law of thermodynamics is the answer here. (delta)Q = (delta)U + (delta)W. The work done by the system is 70 Joules, but 150 Joules of heat was added. Rearrange the first law equation and subtract the work from the input heat to find the increase in internal energy. (delta)Q - (delta)W = (delta)U leads us to 150J - 70J = 80J. 27 / 40 A light ray passes from a material of low refractive index to one of high refractive index. Which of the pairs of quantities listed below describes the light ray as it strikes and passes through the interface between the two materials? Match the descriptions below with the statement that best describes the situation. A part of the light ray remains inside the low refractive index material. The angle of refraction is larger than the angle of incidence. The angle of refraction is equal to the angle of incidence. The angle of reflection is larger than the angle of incidence. The angle of reflection is smaller than the angle of incidence. The angle of incidence equals the angle of reflection. The correct answer is (E). When the light is incident to the surface of the second material, a small amount of reflection occurs even though most of the light passes through the surface interface and into the second substance. This means the law of reflection is in effect for the reflected part of the light ray, the angle of reflection equals the angle of incidence. 28 / 40 Einstein based his theory of relativity on the postulate that photoelectrons absorb and emit photons. the velocity of light is the same for all observers. mass and energy are intra-convertible. the universe is an entropic system. energy and momentum are conserved. The correct answer is (B). One of two postulates of Einstein's theory of special relativity is that the speed of light in a vacuum is the same for all observers. 29 / 40 Which of the following is NOT a correct pairing of physicist and field in which he made significant contributions? Newton ” gravitation Einstein ” relativity Faraday ” electricity and magnetism Coulomb ” quantum mechanics Bohr ” atomic structure Eliminate A because Newton's Law of Universal Gravitation is reason to believe that Newton worked on gravitation. Eliminate B because Einstein may be best known for relativity, so he did work on relativity. Eliminate C because the unit of capacitance is named after Faraday, so Faraday must have worked on electricity and magnetism. For D, though, Coulomb's Law and the unit of electric charge are both named after Coulomb, which suggests that he significantly predated quantum mechanics and worked on the fundamentals of classical electrostatics; in fact, he was most active in the late 1700s, well before the quantum mechanics of the 1920s. Eliminate E because the Bohr model of an atom is definitely a product of Bohr's work on atomic structure. 30 / 40 A 24 V battery is connected to a 4 ohm resistor, causing a current of 5 amperes. What is the internal resistance of the battery? 0 W .8 W .4 W 1.6 W 1.2 W The correct answer is (B). A voltage of 24 V should yield a current of 6A when it is hooked to a 4ohm resistor. The internal resistance of the battery is found . The extra .8ohm of resistance is the internal resistance of the battery. 31 / 40 Two satellites orbit the earth in circular orbits, each traveling at a constant speed. The radius of satellite A's orbit is R, and the radius of satellite B's orbit is 3R. Both satellites have the same mass. How does FA, the centripetal force on satellite A, compare with FB, the centripetal force on satellite B ? FA = 9FB FA = 3FB FA = FB FB = 3FA FB = 9FA Since the centripetal force on each satellite is equal to the gravitational force it feels due to the earth, the question is equivalent to, How does FA, the gravitational force on satellite A, compare to FB, the gravitational force on satellite B? Because both satellites have the same mass, Newton's law of gravitation tells us that the gravitational force is inversely proportional to r2. Since satellite B is 3 times farther from the center of the earth than satellite A, the gravitational force that satellite B feels is the gravitational force felt by satellite A. (Be careful if you tried to apply the formula Fc = for centripetal force and concluded that the answer was B. This is wrong because even though both satellites orbit at a constant speed, they don't orbit at the same speed, so the formula for centripetal force cannot be used directly.) 32 / 40 A driver in an automobile hears a siren behind her and pulls over to let a fire engine pass. The sound of the siren changes as the fire truck approaches, is beside her, and passes her. Which of the following is/are true under these conditions? I. The pitch of the sound increases as the fire truck approaches. II. The wavelength of the sound increases as the fire truck approaches. III. The wavelength of the sound increases after the fire truck passes. I only II only I and III only II and III only I, II, and III The correct answer is (C). The listener hears the sound waves being bunched together as the siren approaches him, causing the pitch of the sound he hears to increase. When the fire truck passes the listener, the sound waves seem to be spread apart as the pitch of the sound decreases due to the lengthening of the sound waves. 33 / 40 While a person lifts a book of mass 2 kg from the floor to a tabletop, 1.5 m above the floor, how much work does the gravitational force do on the book? -30 J -15 J 0 J 15 J 30 J The gravitational force points downward while the book's displacement is upward. Therefore, the work done by gravity is -mgh = -(2 kg)(10 N/kg)(1.5 m) = -30 J. 34 / 40 The density of any substance from the most dense phase to the least dense phase is gas, liquid, solid liquid, solid, gas liquid, gas, solid solid, gas, liquid solid, liquid, gas The correct answer is (E). The atoms and molecules of a solid are packed together more tightly than they are in a liquid. Liquid particles are able to slide over one another, but they are still in contact. Gaseous atoms and molecules have gained enough energy to move away from one another. 35 / 40 The critical angle for a beam of light passing from a diamond into the air is 24.4 degrees. This means that any light rays that strike the surface interface between the diamond and the air with an angle less than 24.4 degrees are completely reflected. partially reflected and partially refracted. completely absorbed. partially absorbed and partially transmitted. completely transmitted. The correct answer is (A). Light rays leaving an optically more dense material and striking the surface interface between the two substances are totally reflected back into the material when the angle of incidence is equal to or less than the critical angle. 36 / 40 An Olympic weight lifter lifts a weight bar weighing 2000N straight up to a height of 2.25 m in a time of .65 seconds. The weight lifter stands holding the weight at that height for the next 4 seconds before dropping the weights to the floor. How much power did the weight lifter use to lift the weights overhead? 2925 watts 3077 watts 4500 watts 6923 watts 9100 watts The correct answer is (D). Power is the rate at which work is done, Power = work/time. The weight lifter lifted the weights up from the floor to a distance of 2.25 m above the floor in a time of .65 seconds. The work the weight lifter did to raise the weights can be calculated either by (FÂ·sÂ·cosÎ¸) or by using the potential energy (mgh). Divide the work by the time he took to raise the weights, and the power he develops is 6923 watts. 37 / 40 Which one is NOT a vector? Displacement Velocity Acceleration Linear momentum Kinetic energy Kinetic energy is a scalar, equal to one-half an object's mass times the square of its speed. Like potential energy and work, kinetic energy does not have a direction associated with it. 38 / 40 A radioactive isotope of iodine has a halflife of 8 hours and causes a counter to register 180 counts/min. Find the count rate for this sample of iodine two days later. 1.4/min 2.8/min 5.6/min 11.2/min 22.4/min The correct answer is (B). Half-life means that half of the substance decays away during that time. Over 48 hours there are 6 half-lives. 39 / 40 2 satellites orbit the earth. Their orbits are circular, and each satellite travels at a constant speed. If the mass of Satellite #2 is twice the mass of Satellite #1, which satellite's speed is greater? Satellite #1, by a factor of Satellite #1, by a factor of 2 Satellite #2, by a factor of Satellite #2, by a factor of 2 Neither; the satellites' speeds are the same. Let m be the mass of a satellite orbiting the earth in a circular orbit of radius r at a constant speed of v. Since the centripetal force is provided by the gravitational force due to the earth (mass M), we can write . Solving for v gives us v = . This result tells us that the mass of the satellite is irrelevant; only the mass of the earth, M, remains in the formula. Since v is inversely proportional to the square root of r, the satellite that's closer will have the greater speed. In this case, since Satellite #1 has the smaller orbit radius, it has the greater speed, and, since the radius of its orbit is 40 / 40 The catcher prepares to receive a pitch from the pitcher. As the ball reaches and makes contact with his glove, the catcher pulls his hand backward. This action reduces the impact of the ball on the catcher's hand because the energy absorbed by his hand is reduced. the momentum of the pitch is reduced. the time of impact is increased. the time of impact is reduced. the force exerted on his hand remains the same. The correct answer is (C). The momentum of the pitched ball is changed by the impulse Ft. The catcher reduces the magnitude of the force on his hand by increasing the time required to change the momentum of the ball. Your score is The average score is 41% LinkedIn Facebook Twitter VKontakte 0% Restart quiz Previous Quiz Next Quiz