43 Created by Master Student Physics Practice Test #3 1 / 40 Traveling at an initial speed of 1.5e6 m/s, a proton enters a region of constant magnetic field, B, of magnitude 1.0 tesla. If the proton's initial velocity vector makes an angle of 30 degrees with the direction of B, compute the proton's speed 4 seconds after entering the magnetic field. 5.0e5 m/s 7.5e5 m/s 1.5e6 m/s 3.0e6 m/s 6.0e6 m/s Since the magnetic force is always perpendicular to the object's velocity, it does zero work on any charged particle. Zero work means zero change in kinetic energy (a direct consequence of the work-energy theorem), so the speed remains the same. Remember: The magnetic force can only change the direction of a charged particle's velocity, not its speed. 2 / 40 A car, starting from rest, accelerates uniformly at 4 m/s2 along a straight track. How far will it travel in 6 s ? 24 m 48 m 64 m 72 m 144 m Using Big Five #2 (with v0 = 0), we get (delta)s = at2 = (4 m/s2)(6 s)2 = 72 m. 3 / 40 A magician pulls a tablecloth from under a table full of dishes without disturbing the dishes. This act demonstrates that gravity holds the dishes still. the weight of the dishes is reduced. action-reaction forces are in operation. the dishes have inertia. the dishes have no acceleration. The correct answer is (D). The inertia of the dishes (Newton's first law) causes them to remain at rest. The fast rate at which the magician pulls the tablecloth from under the dishes keeps the static friction from changing to kinetic friction. 4 / 40 When blue light is shined onto a certain metal, no electrons are ejected. Which of the following lights might eject electrons from the metal? Red Yellow Green Infrared Ultraviolet The correct answer is (E). Of the choices listed, the only electromagnetic radiation that carries more energy than the blue light is ultraviolet. 5 / 40 If a shaft were drilled through the center of the earth and all you had to do was step into the shaft to "fall" to the other side, and a 800N person took the trip, her weight at the exact time she passed through the exact center of the earth would be zero. 800N. less than 800N but more than zero. more than 800N. Need more information. The correct answer is (A). Since , the person will be weightless at the center of the earth because r = 0, and all the mass of the earth is attracting the person from outside the center. 6 / 40 A rock is dropped off a cliff and strikes the ground with an impact velocity of 30 m/s. How high was the cliff? 15 m 20 m 30 m 45 m 60 m Use Big Five #5 with v0 = 0 (calling down the positive direction). 7 / 40 What's the missing particle in the following nuclear reaction? Proton Neutron Electron Positron Gamma To balance the mass number (the superscripts), we must have 196 + 1 = 197 + A, so A = 0. To balance the charge (the subscripts), we need 78 + 0 = 78 + Z, so Z = 0. The only particle listed that has zero mass number and zero charge is a gamma-ray photon, . 8 / 40 A batter hits a long fly ball. Neglecting air resistance, the baseball's horizontal component of speed is constant because it is not acted upon by any forces. is not acted upon by gravitational sources. is not acted upon by any vertical forces. is not acted upon by any horizontal forces. the net forces acting on the baseball are zero. The correct answer is (D). According to Newton's first law, an object in motion remains in motion and an object at rest remains at rest unless a net force acts on the object. The ball is in free fall. Even though it is accelerating on the y axis (up and down), nothing is affecting the ball on the x axis (horizontal) 9 / 40 Refrigerators and freezers perform their functions by converting hot air to cold air. keeping hot air out with cold air pressure. removing heat from inside themselves. blowing cold inside them. producing cold air. The correct answer is (C). Refrigerators and freezers operate in a reversed direction from a heat engine. Instead of using a hot source to produce work, work is done on a warm source and heat is removed, producing the cooling effect. 10 / 40 At the third maxima on both sides of the zeroth fringe in a Young's double slit experiment, the light travels the same distance. from the lower opening travels three times farther than light from the upper opening. from the upper opening travels three times farther than light from the lower opening. from either opening travels 2 wavelengths farther than light from the other opening. from either opening travels 3 wavelengths farther than light from the other opening. The correct answer is (E). Each bright spot is a point at which waves constructively interfere. The waves combine at whole number wavelength intervals. This means at 1, 2, 3, etc., wavelengths.The third maxima is where a three-wave difference in the path length occurs. 11 / 40 A 30N child can push open a 1000N door because the torque the child exerts on the door is greater than the torque the door exerts on the child. the lever arm through which the child's force is exerted is less than the lever arm through which the door's weight is exerted. the door's center of gravity is located at the bottom hinge. the door's center of gravity is located at the top hinge. the door's center of gravity is located at the doorknob. The correct answer is (A). An unbalanced torque causes motion to occur. The child can push the door open because she applies the unbalanced torque. 12 / 40 A 7.25 kg bowling ball is rolled onto a perfectly level surface at a velocity of 10 m/s. The co-efficient of friction between the surface and the bowling ball is .0025. If the surface is perfectly level and is long enough, how far will the bowling ball roll before it comes to a complete stop? 20 m 200 m 2 km 20 km 1/2 km The correct answer is (C). The problem can be solved as a combination work-energy theorem problem. KE = Work is restated as 1/2 mv2 = (Ff)(s)(cosθ). The Ff is found by using the equation for frictional force, Ff = μN. Put it all together and solve 13 / 40 A carbon atom decays into a nitrogen atom in the equation below. Which of the quantities correctly finishes the equation? Alpha Beta Gamma Neutron Neutrino The correct answer is (B). The carbon atom changes into a nitrogen atom. This conversion can only occur if a neutron emits a beta particle as it changes into a proton. 14 / 40 Which of the following best describes the relationship between the frequency and amplitude of a sound wave? Frequency is proportional to amplitude. Frequency is proportional to the square of the amplitude. Frequency is inversely proportional to amplitude. Frequency is inversely proportional to the square of the amplitude. Frequency and amplitude are independent. The frequency determines the pitch of a sound, and the amplitude determines the intensity (or loudness). Pitch and loudness are independent. (A sound can be soft and low pitched, soft and high pitched, loud and low pitched, or loud and high pitched; there's no connection.) 15 / 40 An unmanned exploratory space vehicle is accelerated to .85c as it leaves the solar system. Years later a stationary extraterrestrial watches the vehicle pass and measures the length of the vehicle to be 12.64 m. What was the length of the vehicle on earth before it began its trip? 8.44 m 12.64 m 18.23 m 24.0 m 29.77 m The correct answer is (D). The relativistic equation is . In the eyes of an outside observer, the ship undergoes a contraction. 16 / 40 The kinetic energy a pendulum contains 74. Einstein's theory of relativity is based on when it passes through its zero displacement may be decreased by increasing the mass of the bob. increasing the thickness of the string. decreasing the length of the string. increasing the length of the string. decreasing the displacement of the The correct answer is (E). When the pendulum is displaced, the potential energy the pendulum gains is equal to the height above the zero point to which the pendulum is raised. When the pendulum is released, all the potential energy at its displaced position is converted into kinetic energy. Thus, a smaller displacement gives the pendulum less potential energy, which in turn yields less kinetic energy when the bob moves through the zero point. 17 / 40 Consider a light wave that passes from air into a very thick clear glass block that has its opposite internal side mirrored (facing into the glass). The light ray passes into the glass block at an angle greater than 0 degrees and less than 90 degrees, strikes the mirrored surface and reflects back through the glass into the air. What happens while the light ray is in the glass block but before it strikes the mirrored surface? The wavelength of the waves decreases. The velocity of the waves decreases. The period of the waves increases. The frequency of the waves increases. The frequency of the waves decreases. The correct answer is (D). While the light ray is moving through an optically denser material, its velocity decreases. 18 / 40 Which of the following is an example of a compressional wave? X-ray Cosmic ray Radio wave Light wave Sound wave The correct answer is (E). Sound waves are propagated in a manner that is parallel to their direction of movement. They are composed of a series of compressions and rarefactions. 19 / 40 Consider two adjacent transparent media. The speed of light in Medium 1 is v1, and the speed of light in Medium 2 is v2. If v1 < v2, then total internal reflection will occur at the interface between these media if a beam of light is incident in Medium 1 and strikes the interface at an angle of incidence greater than sin-1(v1/v2). incident in Medium 1 and strikes the interface at an angle of incidence greater than sin-1(v2/v1). incident in Medium 2 and strikes the interface at an angle of incidence greater than sin-1(v1/v2). incident in Medium 2 and strikes the interface at an angle of incidence greater than sin-1(v2/v1). Total internal reflection is impossible in the situation described. In order for total internal reflection to occur, the beam must be incident in the medium with the higher index of refraction and strike the interface at an angle of incidence greater than the critical angle. Since v1 < v2, the refractive index of Medium 1, n1 = c/v1, must be greater than the index of Medium 2 (n2 = c/v2), and the critical angle is θcrit = sin−1 (n2/n1) = sin−1 (v1/v2). 20 / 40 Two high school students attempt to push a car uphill. The car rolls downhill against them for a distance of 10 m before they can bring it to a stop. If both students pushed on the car with a force of 1000N while it rolled downhill, how much work did they do? 1000 J -1000 J 10,000 J -10,000 J The correct answer is (E). Work can be either a positive quantity or a negative quantity. When a force is applied in one direction and the displacement is in the opposite direction, the work equation becomes F·s·csine 180 degrees The cosine of 180 degrees is -1, therefore any work done under those conditions is negative work. W = -F·S = -(1000N)(10 m) = -10,000 J 21 / 40 The energy obtained in a nuclear reaction is derived from mass defect. binding energy. fission. fusion. all of these. The correct answer is (E). The sum of the individual masses of the parts of a nucleus is less than their mass when they are bound into the nucleus-producing mass defect. The mass from the mass defect is converted into the energy that holds the nucleus together and is released in fission. Fusion also produces energy when individual nuclei are forced to combine (fusion) and form new elements in a process that produces energy. 22 / 40 When a switch is closed to operate a DC circuit, the electrons that cause the current travel from the negative plate of the battery to the positive plate. travel from the positive plate of the battery to the negative plate. travel from one resistance to the next resistance. travel from the negative plate of the battery to the positive plate inside the battery. travel from one atom in the circuit to the next atom. The correct answer is (E). The battery that provides the force to push electrons through the circuit causes the electrons to jump from atom to atom, a process that causes the current to flow. The process is similar to water flowing in a hose. Water enters one end of the hose and leaves the other end, but they are not the same water molecules. 23 / 40 Which of the following statements is true about an ideal gas contained at a fixed volume when its temperature is raised? The density of the gas decreases. The average velocity of the gas particles increases. The density of the gas increases. The pressure remains constant. The pressure decreases. The correct answer is (B). The temperature of a gas is directly related to the rate at which gas particles strike the sides of the container in which the gas is contained. The measure of the number of times gas particles strike the sides of the container is pressure. Charles Law shows the direct relationship between the two. When the temperature increases, the pressure increases. This means the velocity of the gas particles increases, too. 24 / 40 A soccer ball, at rest on the ground, is kicked with an initial velocity of 10 m/s at a launch angle of 30 degrees. Calculate its total flight time, assuming that air resistance is negligible. 0.5 s 1 s 1.7 s 2 s 4 s First we determine the time required for the ball to reach the top of its parabolic trajectory (which is the time required for the vertical velocity to drop to zero). 25 / 40 A car is driving along a level road at a constant 60 km/hr. The force acting on the car from the tires of the car is equal to the power of the engine. the normal force times the coefficient of friction. larger than the normal force times the coefficient of friction. less than the normal force times the coefficient of friction. zero. The correct answer is (E). An object that is not being accelerated cannot have any unbalanced forces acting upon it. The car is moving at a constant velocity, which means there are no forces exerted on the car anywhere. 26 / 40 An object is placed inside the focal point of a concave mirror. Which of the following describes the image? Virtual, erect, and reduced Virtual, erect, and magnified Virtual, inverted, and reduced Real, erect, and reduced Real, inverted, and magnified The correct answer is (B). If an object is placed inside the focal point of a concave mirror, so that s < t. the resulting image is virtual (that is, the image point is on the opposite side of the mirror from the object), erect, and larger than the object. 27 / 40 Object A (which is cold) is placed on top of object B (which is hot) in a closed system. Which of the following is the best description of what occurs in the system? I. Both A and B eventually reach the same temperature. II. Gravity stops heat from moving up into A. III. Heat flows from A to B. I only II only I and III only II and III only I, II, and III The correct answer is (A). Gravity has nothing to do with heat transfer. Both objects will reach the same temperature when they have reached equilibrium. 28 / 40 Which of the following statements best describes the relationship between two objects that are in thermal equilibrium? Their masses are equal. Their volumes are equal. Their density is equal. Their heat content is equal. Their temperatures are equal. The correct answer is (E). Two different objects that are in thermal equilibrium must be at the same temperature. 29 / 40 A sample of a radioactive substance has a half-life of 20 minutes. If the sample's activity is 200 counts/second, what is the number of counts/second after one hour passes? 6.25 counts/sec 12.5 counts/sec 25 counts/sec 50 counts/sec 100 counts/sec The correct answer is (C). The sample has three half-lives occurring in one hour.. Next, we have . The original counts are multiplied by the amount ofthe sample remaining: . 30 / 40 How much heat is required to raise the temperature of a 0.04 kg stainless steel spoon from 20 degrees celsius to 50 degrees celsius if the specific heat of stainless steel is 0.50 kJ/kg e degrees celsius ? 200 J 400 J 600 J 800 J 1,000 J Use the equation Q = mc ∆T. 31 / 40 An object is thrown from a moving vehicle. Which of the following statements is not true? I. The velocity of the object changes. II. The acceleration of the object changes. III. The direction of motion of the object changes. I only II only I and III only II and III only I, II, and III The correct answer is (B). When the object leaves the hand of the person who throws it out of the vehicle, the object is in free fall. The acceleration of any object in free fall is a constant 9.8 m/s2, therefore the acceleration does not change. Since there is acceleration, however, the velocity will change. 32 / 40 A 50 g cube of ice is added to 500 g of boiling water. Which of the following is most likely to occur? The ice cube vaporizes before it strikes the bottom of the container. The water boils more vigorously because the hot water draws cold from the ice cube. The water in the container stops boiling during the phase change of the ice to water. The more dense ice cube sinks in the less dense hot water. Steam bubbles form on the ice cube. The correct answer is (C). When the ice cube enters the boiling water, the heat in the water immediately begins to change the phase of the ice to water. Consequently, the higher energy phase change (boiling) stops until the lower energy phase change (melting) is complete. 33 / 40 When it is known that a net force is operating on an object, it is known that the object is moving with constant velocity. losing mass. at rest. being accelerated. gaining weight. The correct answer is (D). Any time a net or unbalanced force is applied to an object, the object is accelerated. 34 / 40 A very rich boy has an ice hockey practice floor that is essentially frictionless installed in a long refrigerated boxcar. As the train is moving, the boy practices shooting at the goal at the other end of the car. Just as he releases his shot, the train goes around a sharp curve to the left (looking forward in the direction the boy is shooting).Which statement most accurately describes the boy's shot? It curves to the right and misses to the right side of the net. It curves to the left and misses to the left side of the net. It travels straight and misses to the right side of the net. It travels straight and misses to the left side of the net. It travels straight into the goal. The correct answer is (C). The two surfaces (hockey puck and ice) are essentially frictionless. The movement of the train around a curve has no effect on the puck, which continues to move in a straight line. The goal does move around the curve with the train. This moves the net to the left, while the puck travels in a straight line. 35 / 40 An electron is allowed to freely move between a pair of parallel plates that have a 1.5 volt potential difference. The electron starts at the negative plate. The velocity of the electron as it strikes the positive plate is most nearly 7.3e-8 m/s 7.3e-5 m/s 7.3e5 m/s 7.3e8 m/s 7.3e11 m/s The correct answer is (C). The voltage of the battery is equal to electrical potential energy, and the kinetic energy is .5mv2. Setting the two equal to each other, .5mv2 = (1.5V)(q). Solving the equation yields 7.3e5m/s, which is the velocity of the electron just as it reaches the positive plate of the battery. 36 / 40 According to Einstein's theory of relativity, which of the following would be a correct assumption to make for a traveler in a spaceship traveling at .95c? Clocks on the spaceship run more slowly. The spaceship will appear shortened. The mass of the spaceship increases while it is in motion. Light travels at the same velocity for the traveler whether he is moving or not moving. All of these assumptions would be correct. The correct answer is (E). All of the choices are correct. Clocks on the spaceship move more slowly, the length of the spaceship would be contracted, the relativistic mass of the spaceship is greater than the rest mass, and the velocity of light is constant for everyone. 37 / 40 An object is placed 60 cm from a spherical convex mirror. If the mirror forms a virtual image 20 cm from the mirror, what's the magnitude of the mirror's radius of curvature? 7.5 cm 15 cm 30 cm 60 cm 120 cm Because the image is virtual, we must write the image distance, si, as a negative quantity: si = -20 cm. Now, with so = 60 cm, the mirror equation gives 38 / 40 A woman dancing in high-heeled shoes accidentally steps on her partner's foot with the heel of her shoe. Even though her partner outweighs her by 400N and can easily lift her off the floor, he feels pain because her weight is concentrated into a small area. her small foot has a large momentum. her foot has a large inertia. his foot has no inertia. his foot has no momentum. The correct answer is (A). The pressure he feels is equal to force per unit area. His partner's heel is a tiny area, which bears most of her weight. This gives a large local force at the small end of her heel. 39 / 40 If an object's mass and the net force it feels are both known, then Newton's second law could be used to directly calculate which quantity? Displacement Velocity Acceleration Linear momentum Kinetic energy Newton's second law is Fnet = ma, so if we know Fnet and m, we can calculate the acceleration, a. 40 / 40 The frequency of a wave is 4 cycles per second, and its speed is .08 meters per second. What is the wavelength of one of the waves? .25 seconds .55 seconds 3.125 seconds .02 seconds 12.55 seconds The correct answer is (D). The wavelength is found by dividing the frequency of the waves into the velocity of the waves λ = v/f. Your score is The average score is 43% LinkedIn Facebook Twitter VKontakte 0% Restart quiz Previous Quiz Next Quiz
