Q&A Hero

Q: As the speed of a particle approaches the speed of light, the momentum of the particle A) approaches zero. B) approaches infinity. C) transforms to energy. D) is no longer in spacetime.

Q: When we apply the Lorentz factor γ to momentum, we A) multiply by γ as with the equation for time dilation. B) multiply by the reciprocal of γ. C) find it does not apply.

Q: When a high-velocity beam of electrons is bent by a magnetic field, relativistic effects A) increase momentum beyond its classical value. B) reduce the angle at which the beam is bent. C) both of these D) neither of these

Q: There is an upper limit on the speed of a particle, which means there is also an upper limit on its A) momentum. B) kinetic energy. C) both of these D) neither of these

Q: When an object of mass m is pushed to relativistic speed v, its momentum is A) greater than mv. B) smaller than mv. C) equal to mv.

Q: A 10-meter-long spear is thrown at relativistic speeds through a 10-meter-long pipe. (Both these dimensions are measured when each is at rest.) When the spear passes through the pipe A) the spear appears to shrink so the pipe completely covers it. B) the pipe appears to shrink so the spear extends from both ends. C) both appear to shrink equally so the pipe barely covers the spear. D) any of these, depending on the motion of the observer (moving with the spear, at rest with the pipe, and so on). E) none of the above

Q: Radioactive muons formed high in the atmosphere have an average lifetime of 2 millionths of a second and travel toward Earth at nearly the speed of light. Because of their altitude most of them should have decayed by the time they reach the Earth's surface, according to pre-relativity physics. They don't because they A) live longer due to time dilation. B) travel a shorter distance due to length contraction. C) both of these D) neither of these

Q: A heavy meterstick has mass m. When the meterstick is thrown like a spear past you at speed v, you measure its momentum to be 2mv. What do you measure its length to be? A) 1 m B) 0.87 m C) 0.5 m D) 0.25 m E) none of the above

Q: The length of a 100-meter long spaceship passing by you at 0.87c is seen to be A) 50 m. B) 87 m. C) 100 m. D) 125 m. E) 150 m.

Q: An astronaut traveling forward at 0.87c holds a meterstick in spear-like fashion. An observer at rest sees the spear's length as A) 0.5 m. B) 0.87 m. C) 1 m. D) 1.25 m. E) 1.5 m.

Q: An astronaut traveling forward at 0.87c holds a meterstick in spear-like fashion. This astronaut sees the spear's length as A) 0.5 m. B) 0.87 m. C) 1 m. D) 1.25 m. E) 1.5 m.

Q: A spaceship whizzes past a planet at high speed. An observer on the planet sees a contracted spaceship, while an observer on the spaceship sees A) a contracted planet. B) an expanded planet. C) a normal planet. D) a contracted or expanded planet depending on the direction of travel.

Q: To outside observers at rest, the overall sizes of objects traveling at relativistic speeds are A) larger. B) smaller. C) the same size.

Q: A girl standing on the ground observes a rocket ship move past her at half the speed of light. Compared to the rocket's length at rest, she sees the rocket's length as A) longer. B) shorter. C) the same length.

Q: When we apply the Lorentz factor γ to length contraction, we A) multiply by γ as in the equation for time dilation. B) multiply by the reciprocal of γ C) find it does not apply.

Q: Objects moving at relativistic speeds appear to observers at rest to be A) stretched. B) shrunken. C) either depending on direction of motion. D) none of the above

Q: Relative to some reference frame in the universe, you may now be traveling at a speed A) faster than the speed of light. B) slower than the speed of light. C) at the speed of light. D) any of the above

Q: According to special relativity, tomorrow's travelers can travel A) only forward in time. B) backward in time. C) both forward and backward in time.

Q: As a spaceship moving toward you at half the speed of light fires a probe toward you, relative to itself at 0.7 the speed of light, you see the probe approaching at about A) 0.70c. B) 0.87c. C) 0.89c. D) 0.92c. E) 0.96c.

Q: As a spaceship moves away from you at half the speed of light, it fires a probe, also away from you at half the speed of light relative to the spaceship. Relative to you, the probe moves at A) 0.80c. B) 0.87c. C) 0.90c. D) 0.95c. E) c.

Q: Using the relativistic velocity-addition formula for adding everyday velocities produces A) nonsense. B) a significantly better result than adding them classically. C) a classical result.

Q: Two spaceships approaching each other move at very close to the speed of light, each sending a beam of light to the other. Each measures the speed of light from the other spaceship as A) slightly less than c. B) c. C) slightly greater than c. D) much greater than c.

Q: A spaceship traveling very fast relative to you fires a stream of photons at speedc away from you. You measure the photons' speed to be A) less than c. B) more than c. C) equal to c.

Q: The most abundant element in the universe is A) hydrogen. B) helium. C) lead. D) uranium.

Q: Earth's interior is warmed by ________ and Earth's surface is warmed by ________. A) radioactive processes; fusion in the Sun B) fission; fossil fuels C) volcanoes; solar energy D) terrestrial radiation; terrestrial radiation

Q: Sustained energy output by fusion is a daily occurrence in A) military installations. B) breeder reactors. C) the Sun. D) Earth's interior.

Q: Early 21st Century research in nuclear fusion uses A) laser beams. B) ultra-hot plasmas. C) both of these D) neither of these

Q: Deuterium and tritium are both A) forms of hydrogen. B) isotopes of the same element. C) both of these D) neither of these

Q: Compared with the energy produced by fissioning a gram of uranium, the energy produced by fusing a gram of deuterium is A) more. B) less. C) the same.

Q: Fusing two iron nuclei would occur with A) absorption of energy. B) release of energy. C) neither of these

Q: Fusing two carbon nuclei would occur with A) absorption of energy. B) release of energy. C) neither of these

Q: Fissioning carbon would occur with A) absorption of energy. B) release of energy. C) neither of these

Q: Iron is a poor choice of nuclear fuel because it releases A) energy only when fused. B) energy only when fissioned. C) no energy when fused or fissioned.

Q: If oxygen were used as nuclear fuel, it would be best A) fused. B) fissioned. C) either of these

Q: If gold were used as nuclear fuel, it would be best A) fused. B) fissioned. C) either of these

Q: When U-235 undergoes fission, the total number of protons in the fragments is A) 90. B) 91. C) 92. D) 93. E) none of the above

Q: Detonation of a fusion-type hydrogen bomb begins by A) splitting uranium. B) pressing together pieces of uranium. C) igniting a fission bomb. D) all of the above E) none of the above

Q: Detonation of a fission-type uranium bomb begins by A) splitting uranium. B) pressing together pieces of uranium. C) igniting a small conventional bomb. D) all of the above E) none of the above

Q: When two light atoms fuse together, mass A) converts to kinetic energy. B) converts to high-energy gamma radiation. C) is created from energy of other forms. D) is gained.

Q: An element is changed into a completely different element in A) radioactive alpha decay. B) radioactive beta decay. C) nuclear fission. D) nuclear fusion. E) all of the above

Q: In both fission and fusion, mass A) is created from energy of other forms. B) converts to kinetic energy. C) converts to gamma radiation. D) remains the same.

Q: Fissioning an iron nucleus would occur with A) absorption of energy. B) release of energy. C) neither absorption nor release of energy

Q: In both fission of uranium and fusion of hydrogen, mass A) decreases. B) remains constant. C) increases.

Q: According to the "energy valley" of the mass-per-nucleon versus atomic-number graph, the element with the least mass per nucleon is A) hydrogen. B) helium. C) iron. D) uranium. E) none of the above

Q: Between the processes of nuclear fission and fusion, radioactive by-products are more characteristic of nuclear A) fission. B) fusion. C) both of these D) neither of these

Q: The nuclear process having by-products with least radioactivity is A) fission. B) fusion. C) about the same for both.

Q: The energy released in both fission and fusion is mainly in the form of A) kinetic energy of fragments. B) alpha radiation. C) beta radiation. D) gamma radiation. E) none of the above

Q: Energy released by the Sun results from the process wherein atomic nuclei A) break apart. B) combine. C) both of these D) neither of these

Q: An important feature of the mass spectrometer is that A) all ions enter the device at equal speeds. B) ions of different masses bend differently. C) the greater an ion's mass, the wider its circular arc. D) a magnetic field exerts forces on moving charged particles. E) all of the above

Q: A mass spectrometer separates A) ions of different elements. B) different-mass ions of the same element. C) different-mass ions of the same speed. D) all of the above E) none of the above

Q: Various singly-ionized atomic nuclei of the same speed are directed into a magnetic field in a mass spectrometer where they are deflected and strike a detecting screen. The particles most strongly deflected are those of A) least mass. B) greatest mass. C) same for all

Q: Compared with the sum of isolated-nucleon masses, their collective mass in a composite nucleus is A) more. B) less. C) the same.

Q: Fissioning a lead nucleus would yield a net A) absorption of energy. B) release of energy. C) neither of these

Q: The nucleus having the most tightly bound nucleons is A) hydrogen. B) iron. C) lead. D) uranium. E) plutonium.

Q: The nucleus that has the greatest mass per nucleon is A) hydrogen. B) iron. C) lead. D) uranium. E) plutonium.

Q: The nucleus that has the least mass per nucleon is A) hydrogen. B) iron. C) lead. D) uranium. E) plutonium.

Q: Which of these nuclei has the least mass? A) hydrogen B) iron C) lead D) uranium E) all the same

Q: A nucleon has more mass on average when it is A) inside the nucleus. B) removed from the nucleus. C) both the same

Q: The products of nuclear fission are radioactive due to their A) combustive natures. B) capacity to hold vast amounts of energy. C) greater neutron to proton ratio compared with stable nuclei in the same mass range. D) short half-lives. E) none of the above

Q: To pluck a nucleon from a nucleus requires A) work. B) kinetic energy. C) potential energy. D) none of the above

Q: What is the central equation of mass-energy equivalence? A) W = Fd B) KE = mv2 C) m = F/a D) E = mc2

Q: The fact that more radioactive particles are spewed from coal-fired power plants than nuclear fission reactors is evidence that A) coal is more radioactive than uranium. B) coal-fired plants have less shielding. C) coal-fired plants are more numerous. D) all of the above E) none of the above

Q: The disadvantages to fission power plants include A) radioactive waste disposal. B) production of plutonium for possible weapons proliferation. C) risk of accidental release of radioactivity. D) all of the above E) none of the above

Q: Relative to a fossil-fuel plant, a nuclear power plant produces A) more electricity. B) less heat and smoke. C) less pollution. D) all of the above E) none of the above

Q: The percentage of electricity from nuclear power generated in recent decades in the United States has been about A) 10%. B) 20%. C) 30%. D) 40%. E) more than 40%

Q: The energy output of a typical nuclear reactor is via A) heating water to form steam. B) directing steam to a turbine. C) spinning a turbine to generate electricity. D) all of the above E) none of the above

Q: Plutonium is extremely rare in natural ore deposits because it A) is artificially created. B) is chemically inert. C) is a gas at room temperature. D) has a tiny half-life compared with the age of Earth. E) none of the above

Q: When a nucleus of U-238 absorbs a neutron and becomes U-239, a beta emission, then another beta emission results in A) Th-239. B) Pa-239. C) U-235. D) Pu-239. E) Pb-206.

Q: Plutonium is radioactively toxic A) in any form. B) although less toxic than radium. C) both of these D) neither of these

Q: If all the uranium in the world were exhausted, breeder reactors would be A) in greater demand. B) relics of a brief age. C) both of these D) neither of these

Q: Reactions that take place in a breeder reactor change A) elements into different elements. B) molecules into different molecules. C) ions into different ions. D) all of the above E) none of the above

Q: What does a breeder reactor "breed?" A) more energy output than energy input B) fissionable isotopes from a non-fissionable isotopes C) more mass than it begins with D) all of the above E) none of the above

Q: Although plutonium alone is chemically toxic, it is not toxic when A) oxidized. B) ionized. C) subcritical. D) none of the above

Q: U-235 and Pu-239 are both A) radioactive isotopes. B) fissionable isotopes. C) heavier than lead. D) all of the above E) none of the above

Q: When neptunium emits a beta particle the result is A) a different isotope of neptunium. B) uranium. C) plutonium. D) lead. E) none of the above

Q: Carbon was used in Fermi's first nuclear reactor to A) slow neutrons. B) increase the speed of neutrons. C) absorb neutrons. D) none of the above

Q: Compared with a neutron bouncing off a carbon nucleus, a neutron bouncing off an iron nucleus loses A) less speed. B) more speed. C) the same amount of speed.

Q: A neutron bouncing off a heavy nucleus loses speed. If it instead bounces off a light nucleus it loses A) less speed. B) more speed. C) the same amount of speed.

Q: A neutron will more likely slow in speed if it bounces from a A) light-weight nucleus. B) nucleus of moderate mass. C) heavy nucleus. D) none of the above

Q: The function of graphite in the first atomic reactor was to A) slow fast neutrons. B) emit fast neutrons. C) moderate uranium isotopes. D) none of the above