22 Created by Master Student Physics Practice Test #8 1 / 40 During a collision between two objects, the kinetic energy is conserved. Which statement best describes the momentum after the collision? The momentum equals the kinetic energy. The momentum may be conserved. The momentum must be conserved. The momentum decreases by half. The momentum increases to double the original value. The correct answer is (C). This answer is a statement of the law of conservation of momentum. Momentum before an event equals the momentum after an event. 2 / 40 The images formed by convex mirrors are always real. are always virtual. are only real when the object is placed outside the radius of curvature. are only virtual when the object is placed inside the focal point. None of the above describes the images formed by convex mirrors. The correct answer is (B). Convex mirrors only produce virtual images. That is because the light rays are diverged when they are incident to the surface of the mirror 3 / 40 rue statements about the relationship between the electric field and electric potential include which of the following? I. If the electric field at a certain point is zero, then the electric potential at the same point is also zero. II. If the electric potential at a certain point is zero, then the electric field at the same point is also zero. III. The electric potential is inversely proportional to the strength of the electric field. I only II only I and II only I and III only None of the above 1 E A counterexample for I is provided by two equal positive charges; at the point midway between the charges, the electric field is zero, but the potential is not. A counter-example for II is provided by an electric dipole (a pair of equal but opposite charges); at the point midway between the charges, the electric potential is zero, but the electric field is not. As for III, consider a single positive point charge +Q. Then at a distance r from this source charge, the electric field strength is E = and the potential is V = . Thus, V = rE, so V is not inversely proportional to E. 4 / 40 What is the one factor that distinguishes each element from every other element? The number of protons in the nucleus The number of neutrons in the nucleus The number of electrons about the nucleus The total mass of the nucleus (protons plus neutrons) Its position on the periodic table The correct answer is (A). The only single factor that makes each element unique is the number of protons the element has in its nucleus. 5 / 40 In Young's double-slit interference experiment, what is the difference in path length of the light waves from the two slits at the center of the first bright fringe above the central maximum? λ λ λ λ Since the fringe is bright, the waves must interfere constructively. This implies that the difference in path lengths must be a whole number times the wavelength, eliminating B, C, and E. The central maximum is equidistant from the two slits, so ∆ℓ = 0 there. At the first bright fringe above the central maximum, we have ∆ℓ = λ. 6 / 40 A bicycle wheel spins on its axis at a constant rate but has not yet made a complete rotation. Which of the following statements is correct? The angular displacement is zero. The linear displacement is zero. The angular acceleration is zero. The angular velocity is zero. None of these is zero. The correct answer is (C). The wheel is moving at a constant rate (angular velocity). There is no angular acceleration because (delta)ω is zero. 7 / 40 Which provides the basis for the observation that the universe is expanding? 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 The red shift of light refers to the increase in the wavelength (or, equivalently, the decrease in the frequency) of light from a distant source when it's measured here. This change in wavelength (and frequency) is the Doppler effect and implies that the source and detector are moving away from each other. This provides evidence for the expansion of the Universe. 8 / 40 A block of mass m = 4 kg on a frictionless, horizontal table is attached to one end of a spring of force constant k = 400 N/m and undergoes simple harmonic oscillations about its equilibrium position (x = 0) with amplitude A = 6 cm. If the block is at x = 6 cm at time t = 0, then which of the following equations (with x in centimeters and t in seconds) gives the block's position as a function of time? x = 6 sin(10t + Ï€) x = 6 sin(10Ï€t) x = 6 sin(10Ï€t - Ï€) x = 6 sin(10t) x = 6 sin(10t -Ï€) The only equation that gives x = 6 when t = 0 is the one in A. 9 / 40 Which of the following must always be true? I. If an object's acceleration is constant, then it must move in a straight line. II. If an object's acceleration is zero, then its speed must remain constant. III. If an object's speed remains constant, then its acceleration must be zero. I and II only I and III only II only III only II and III only I is false since a projectile experiencing only the constant acceleration due to gravity can travel in a parabolic trajectory. II is true: Zero acceleration means no change in speed (or direction). III is false: An object whose speed remains constant but whose velocity vector is changing direction is accelerating. 10 / 40 Whether a substance is a solid, liquid or gas is determined by conductivity. number of protons. temperature. number of neutrons. resistively. The correct answer is (C). The physical characteristics of melting and boiling are directly related to how much thermal energy a substance contains. The measure of the thermal energy is temperature. P = (0.5 A)2(100 ohm) = 25 W = 25 J/s E = Pt = (25 J/s)(20 s) = 500 J 11 / 40 A uniform bar is lying on a flat table. Besides the gravitational and normal forces (which cancel), the bar is acted upon by exactly two other forces, F1 and F2, which are parallel to the surface of the table. If the net force on the rod is zero, then which one of the following is true? The net torque on the bar must also be zero. The bar can accelerate translationally if F1 and F2 are not applied at the same point. The net torque will be zero if F1 and F2 are applied at the same point. The bar cannot accelerate translationally or rotationally. None of the above Since Fnet = F1 + F2 = 0, the bar cannot accelerate translationally, so B is false. The net torque does not need to be zero, as the following diagram shows (eliminating A and D). 12 / 40 Characteristics of simple harmonic motion include which of the following? I. The acceleration is constant. II. The restoring force is proportional to the displacement. III. The frequency is independent of the amplitude. II only I and II only I and III only II and III only I, II, and III The acceleration of a simple harmonic oscillator is not constant, since the restoring force ”and, consequently, the acceleration ”depends on position. Therefore, I is false. However, both II and III are fundamental, defining characteristics of simple harmonic motion. E = hf = (4.14e-15 eV * s)(7.2e15 Hz) = 30 eV Kmax = E - ø = 30 eV - 6 eV = 24 eV 13 / 40 During each cycle, a heat engine with an efficiency of 25% takes in 800 J of energy. How much waste heat is expelled during each cycle? 100 J 200 J 300 J 400 J 600 J If the efficiency of the engine is 25%, then the energy that is output for useful work is 25% of the input energy, which is (25%)(800 J) = 200 J. The remaining 800 J - 200 J = 600 J is expelled as waste heat. 14 / 40 When a light ray strikes a perfectly reflective mirror at an angle, which of the following happens? The frequency of the light ray changes. The wavelength of the light ray changes. The velocity of the light ray changes. The period of the light ray changes. The direction of motion of the light ray changes. The correct answer is (E). The process of reflection occurs when the direction of a wave is changed because the wave strikes a barrier (which in this occasion is a mirror). 15 / 40 Each and every person on earth is made of atoms that originated in the food we eat. the ancient stars. our mother's body. the oceans. the earth. The correct answer is (B). All the elements on the periodic table were combined in the fusion furnace of some past star. In fact all substances in existence were formed from elements which were formed in stars. 16 / 40 The processes of constructive interference and destructive interference occur in cosmic rays. light rays. sound waves. water waves. all of these. The correct answer is (E). All of the choices exhibit a wave nature at some time. All waves can interfere with one another, either constructively or destructively. 17 / 40 The force a magnetic field exerts on an electron is largest when the path of the electron is oriented in the opposite direction from the magnetic field's direction. in the same direction as the magnetic field's direction. up through the magnetic field at a 45 degrees angle. down through the magnetic field at a 45 degrees angle. at a right angle to the magnetic field. The correct answer is (E). The largest force a magnetic field exerts on a moving charged particle occurs when the particle crosses the most lines of force. This occurs when the particle enters a magnetic field at right angles to the field. 18 / 40 All of the following are examples of electromagnetic waves EXCEPT X-rays. gamma rays. sound waves. radio waves. light waves. The correct answer is (C). All of the waves are electromagnetic waves except for sound waves. 19 / 40 A student uses a magnetic compass to perform a laboratory experiment in the Northern Hemisphere. She then carries the same magnetic compass with her to the Southern Hemisphere, taking care not to damage the compass in any way. When she reaches her destination at the equivalent latitude and longitude in the Southern Hemisphere, she prepares to perform the same laboratory experiment. The student looks at the compass before performing the experiment to see if the compass needle has changed. How has the compass changed? The compass needle points 90 degreesto the left of the expected direction. The compass needle points 90 degreesto the right of the expected direction. The compass needle slowly rotates in a counter-clockwise direction. The compass needle slowly rotates in a clockwise direction. There has been no change in the compass. The correct answer is (E). The compass is unaffected by the change from the Northern Hemisphere to the Southern Hemisphere. It will work in the same manner all over the world. The magnetic needle points toward the Magnetic North Pole in the Northern Hemisphere. 20 / 40 The symbols used in writing nuclear equations. Atomic nuclei are typically written in the form . Which letter represents the name of the nuclide? The number of protons is Z. The number of neutrons is X. The symbol of the element is X. The number of electrons is A. The mass number is A. The correct answer is (C). The name of the nuclide is represented by the symbol of the element. The X represents the elemental symbol for any one of the elements. 21 / 40 The purpose of a transformer is to do which of the following? Change voltage Reduce resistance Decrease heat transfer Increase magnetic fields Reverse current flow The correct answer is (A). Transformers are used to change voltages to a form that is usable for specific applications. For example, an electrical line voltage of 1800 V is reduced by a transformer to the voltage we use in our homes. 22 / 40 How does one use the right hand rule to determine the direction of the force applied to a current carrying wire? Point the fingers of the right hand in the same direction as the magnetic lines of force. Point the thumb at right angles to the lines of force. Point the fingers of the right hand along the wire in the direction of the current. Point the thumb in the direction of the magnetic lines of force. Point the fingers of the right hand against the direction of the magnetic lines of force. The correct answer is (A). The second step of the right-hand rule is appropriate to answer the question. The entire right-hand rule is restated below 23 / 40 An electric current is applied to a gas discharge tube, causing it to glow. When the discharge is viewed through a spectroscope, which type of spectrum is seen? Monochromatic Continuous Line absorption Line spectra Polarimeter The correct answer is (D). The energized atoms of the gas emit energy in specific regions of the visible spectrum called line spectra. 24 / 40 If 50g of water at a temperature of 30 degrees celsius is added to 200g of water at a temperature of 100 degrees celsius,what will the new temperature of the water be? 68 degrees celsius 80 degrees celsius 74 degrees celsius 86 degrees celsius 92 degrees celsius The correct answer is (D). This is a calorimetry problem (cm(delta)T)cold = (cm(delta)T)hot. The specific heats are the same for both hot and cold water, which may be factored out of the problem, leaving (m(delta)T)cold = (m(delta)T)hot. The answer is 86 degrees celsius. 25 / 40 Materials called dielectrics are placed between the plates of capacitors to speed the current flow. slow the current flow. reduce change leakage from the capacitor. increase capacitance of the capacitor. decrease capacitance of the capacitor. The correct answer is (D). A dielectric is used in a capacitor to increase the capacitance of the capacitor. 26 / 40 Two objects A and B are placed into free fall 14.7 m above the ground at exactly the same time. Object A reaches the ground in exactly 1 second, and object B reaches the ground in exactly 3 seconds. Which of the following is/are true? I. Object B was thrown horizontally. II. Both objects were thrown. III. Neither object was thrown. I only II only I and III only II and III only I, II, and III The correct answer is (B). Neither object could reach the ground in 1 second unless it was thrown downward. Therefore one of the objects, A, was thrown downward. The other object, B could not have been placed into free fall from rest and taken 3 seconds to reach the ground from a height of 14.7 m because it only takes 1.73 seconds to reach the ground for an object starting from rest. The object that takes 3 seconds to reach the ground must therefore have been thrown upward. This means both objects were thrown. 27 / 40 A metal whose work function is 6.0 eV is struck with light of frequency 7.2e15 Hz. What is the maximum kinetic energy of photoelectrons ejected from the metal's surface? 7 eV 13 eV 19 eV 24 eV No photoelectrons will be produced. The energy of the incident photons is 28 / 40 An astronaut is standing on an asteroid when he accidentally drops a wrench. He observes that the gravitational acceleration on the asteroid is 2.4 m/s2. If he had thrown the wrench at an upward angle instead, he would have found the gravitational acceleration on the asteroid to be less than 2.4 m/s2. toward him at 2.4 m/s2. downward at 2.4 m/s2. greater than 2.4 m/s2. none of these. The correct answer is (C). Regardless of the direction of motion for an object in free fall near a large body, the gravitational acceleration exerted by the large body on the smaller body does not change. 29 / 40 Through a series of thermodynamic processes, the internal energy of a sample of confined gas is increased by 560 J. If the net amount of work done on the sample by its surroundings is 320 J, how much heat was transferred between the gas and its environment? 240 J absorbed 240 J dissipated 880 J absorbed 880 J dissipated None of the above By convention, work done on the gas sample is designated as negative, so in the first law of thermodynamics, ∆U = Q - W, we must write W = -320 J. Therefore, Q = ∆U + W = 560 J + (-320 J) = +240 J. Positive Q denotes heat in. 30 / 40 Scientists can determine whether a star is approaching the earth by looking at its red shift. blue shift. rate of shimmer. brightness. absolute magnitude. The correct answer is (B). The Doppler Shift is useful for all kinds of waves, including light. When a star or any object that is producing waves approaches, the individual wave fronts are contacted at a higher rate. In the case of stars, the higher rate at which the wave fronts are contacted causes the starlight to move toward the blue range. 31 / 40 A laser beam passes from the air into a piece of plexiglass. All of the following are false EXCEPT the velocity decreases. the wavelength increases. the frequency decreases. the period decreases. None of the above is true. The correct answer is (A). Light slows down in an optically more dense material. Additionally, the wavelength shortens. The frequency remains the same. Since the frequency remains unchanged, the period also remains the same. 32 / 40 A 1,000 kg car rolls without friction down a hill that is 20 m long and inclined at 15 degrees celsius from the horizontal. What is the velocity of the car at the bottom of the hill? 2 m/s 5 m/s 10 m/s 20 m/s 30 m/s The correct answer is (C). The car rolls down a 20 m long incline that is raised at 15 degrees from the horizontal. Using trigonometry (sin 15 degrees)(20 m) we find the car "falls" 5.125 m. Using the PE = KE relationship, we have mgh = .5mv2. The masses factor out, leaving gh = .5v2, leading to v = . The answer is 10 m/s. 33 / 40 As a rock of mass 4 kg drops from the edge of a 40-meter-high cliff, it experiences air resistance, whose average strength during the descent is 20 N. At what speed will the rock hit the ground? 8 m/s 10 m/s 12 m/s 16 m/s 20 m/s Apply conservation of mechanical energy (including the negative work done by Fr, the force of air resistance). 34 / 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. The light ray inside the material with the higher index of refraction bends toward the normal. The frequency of the wave increases. The frequency of the wave decreases. The velocity of the wave increases. The velocity of the wave decreases. Interference from reflected waves causes the light ray to refract. The correct answer is (D). The material with the higher index of refraction has a greater optical density to the light. The ray bends toward the normal when it slows down in the optically more dense material 35 / 40 The planet Pluto has 1/500 the mass and 1/15 the radius of Earth. What is the value of g on the surface of Pluto? 0.3 m/s2 1.6 m/s2 2.4 m/s2 4.5 m/s2 7.1 m/s2 The gravitational acceleration at the surface of a planet of mass M and radius R is given by the equation g = GM/R2. Therefore 36 / 40 A string, fixed at both ends, supports a standing wave with a total of 4 nodes. If the length of the string is 6 m, what is the wavelength of the wave? 0.67 m 1.2 m 1.5 m 3 m 4 m The distance between successive nodes is always equal to λ. If a standing wave on a string fixed at both ends has a total of 4 nodes, the string must have a length L equal to 3(λ). If L = 6 m, then λ must equal 4 m. 37 / 40 During a pool game the cue ball is shot at the red ball. When the cue ball strikes the red ball, the cue ball stops dead, and the red ball moves away at the same velocity the cue ball had before the collision. The type of collision represented in this example is an elastic collision. a perfectly inelastic collision. an inelastic collision. all of the above. none of the above. The correct answer is (A). This is an example of an elastic collision. The momentum of the cue ball transfers to the red ball. 38 / 40 The volt is a measure of electrical potential and may be defined as opposition to electrical motion. number of particles in motion. work per unit charge. field strength per unit of force. electrostatic discharge. The correct answer is (C). The volt is defined as the force required to move a unit charge through a distance, or the work done per unit charge. 39 / 40 Electrical energy is converted into mechanical energy by which of the following? Magnet Transformer Motor Generator Battery The correct answer is (C). Motors are used in a variety of mechanical devices such as saws, sanders, drills, and pumps. The electric energy is converted to mechanical energy by the rotation of a loop of wire in a magnetic field. 40 / 40 Protons are found in the nucleus of the atom. The nuclear protons with the greatest mass are located in the hydrogen atom. in the carbon atom. in the iron atom. in the radon atom. in the uranium atom. The correct answer is (A). Due to the mass that is converted in the nucleus (mass defect) to hold the protons together in the nucleus, the proton does not have the same mass when it is inside the nucleus as it has outside the nucleus. The hydrogen proton is the proton that is least affected because it is the only proton in the hydrogen atom. Your score is The average score is 36% LinkedIn Facebook Twitter VKontakte 0% Restart quiz Previous Quiz Next Quiz
