Q&A Hero

Q: Important support for general relativity came from studies of the precession of the orbit of A) Mercury. B) Venus. C) Earth. D) Mars. E) asteroids.

Q: A message from relativity theory is that slowing the aging process A) can occur with correct applications of physics. B) would occur if you fell into a bottomless mine shaft. C) can only happen to "the other guy."

Q: According to relativity theory, you can experience a longer youth when you A) are near a black hole. B) are near a very large gravitational field. C) travel at nearly the speed of light. D) all of the above E) none of the above

Q: If the Sun collapsed to a black hole, Earth would A) be sucked into the black hole. B) follow a straight-line path into space. C) continue in its present orbit.

Q: If the Sun collapsed to a black hole, Earth's speed in space would A) increase. B) decrease. C) remain the same.

Q: An astronaut falling into a black hole would see the universe A) red-shifted. B) blue-shifted. C) with no shift at all.

Q: In gravitational red shift, the quantity that undergoes a red shift is A) spacetime curvature. B) wave direction. C) field intensity. D) wave frequency. E) none of the above

Q: According to general relativity, a photon emitted by a star A) loses energy. B) reduces in frequency. C) is red-shifted. D) all of the above E) none of the above

Q: A clock on the surface of a shrinking star will run progressively A) slower. B) faster. C) no difference

Q: You shine a beam of monochromatic light from Earth to an astronaut friend in orbit. The light your friend receives, relative to light from an equivalent source on the spaceship, is slightly A) slower in speed. B) higher in speed. C) neither of these

Q: If you move a clock from Earth to the Moon, the clock runs A) slower. B) no differently. C) faster.

Q: You shine a beam of monochromatic light from Earth to an astronaut friend in orbit. The light your friend receives, relative to light from an equivalent source on the spaceship, is slightly A) lower in frequency. B) higher in frequency. C) weaker but no different in frequency.

Q: On a giant rotating turntable are two clocks, one at the center and the other at the rim.The clock that runs slower is at A) the center of the turntable. B) the rim of the turntable. C) either of these

Q: In accord with general relativity, a person living at the top of a skyscraper ages A) faster than a person on the ground floor. B) slower than a person on the ground floor. C) at the same rate as a person on any floor.

Q: If you move in the direction in which gravity acts, an observer at rest sees your watch running A) slower than at your starting point. B) faster than at your starting point. C) neither of these

Q: Light bends when it A) closely passes a star. B) closely passes the Moon. C) both of these D) neither of these

Q: In a 1-g gravitational field, 1 second after turning on a flashlight its beam will curve beneath a perfectly straight line by A) less than 4.9 m. B) 4.9 m. C) more than 4.9 m.

Q: Fire a cannonball with enormous speed from a hypothetical cannon and it curves due to gravity. Shine a light from a flashlight parallel to the cannon and it A) follows a straight-line path. B) curves downward as much as the cannonball. C) curves slightly upward.

Q: Inside an accelerating spaceship far from gravitational influences, a flashlight beam will A) not bend. B) curve as it would in a gravitational field equal to the acceleration of the spaceship. C) follow a semi-circular path.

Q: If you shine a flashlight "horizontally" from one wall to an opposite wall inside an accelerating spaceship in deep space, you will see the light traveling A) in a straight-line path. B) in a parabolic path. C) along the arc of a circle.

Q: If you shine a flashlight from one wall to an opposite wall inside a spaceship drifting without acceleration far from gravitational influences, the beam of light will travel A) in a straight-line path. B) in a parabolic path. C) along the arc of a circle.

Q: Inside an accelerating spaceship in deep space, a sideways-tossed ball will A) curve as it would in a gravitational field equal to the spaceship's acceleration. B) follow a straight-line path from one side of the interior to the other. C) fall in a semi-circular path.

Q: If you toss a ball "horizontally" from one wall to an opposite wall inside an accelerating spaceship in deep space, defining "up" as the direction of acceleration, the ball will hit A) below its straight-line path. B) above its straight-line path. C) neither of these

Q: According to the principle of equivalence, observations made of falling objects at Galileo's Leaning Tower of Pisa are indistinguishable from observations made in A) a spaceship orbiting in a gravitational field. B) a spaceship accelerating at g in deep space. C) any uniformly moving reference frame. D) all of the above E) none of the above

Q: In a spaceship with an acceleration more than g far from gravitational influences, with the effort it takes on Earth to do 20 pushups, you could comfortably do A) less than 20 pushups. B) 20 pushups. C) more than 20 pushups.

Q: In a spaceship that accelerates at g far from gravitational influences, with the effort it takes on Earth to do 20 pushups, you could comfortably do A) less than 20 pushups. B) 20 pushups. C) more than 20 pushups.

Q: Galileo dropped two balls of different weights and found they accelerated equally to the ground below. Einstein imagined the same result for a side-by-side drop A) without invoking gravity. B) in an accelerating vehicle. C) whether they were of the same mass or not. D) all of the above E) none of the above

Q: Compared with special relativity, general relativity is more concerned with A) acceleration. B) gravitation. C) spacetime geometry. D) all of the above E) none of the above

Q: Relativity equations for time, length and momentum hold true for A) relativistic speeds. B) everyday low speeds. C) both of these D) neither of these

Q: When an electron and a positron meet and annihilate, the mass-energy of the particles is carried away by A) a gamma ray. B) two gamma rays, otherwise momentum wouldn't be conserved. C) nothing at all, gone.

Q: If an antimatter meteor of mass m were to strike the Earth, the amount of radiant energy produced would be A) less than mc2. B) mc2. C) 2mc2. D) none of the above

Q: When you shake an apple to and fro, you're shaking A) energy. B) nothing. C) the universe.

Q: According to the well-known equation E = mc2, A) mass and energy travel at the speed of light squared. B) energy is actually mass traveling at the speed of light squared. C) mass and energy travel at twice the speed of light. D) mass and energy are related. E) none of the above

Q: According to Einstein's theory of special relativity A) space and time are aspects of each other. B) energy and mass are aspects of each other. C) both of these D) neither of these

Q: What does c2 have in common with γ? A) they are both proportionality constants B) they have similar numerical values C) they both involve different kinds of speed D) all of the above

Q: Electrons fired in vintage TV tubes traveled at about 0.25 times the speed of light, having more momentum and energy than would be required classically to get that speed. Strictly speaking, this A) increased your electric bill. B) decreased your electric bill. C) had no effect on your electric bill.

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: As you recede from a steady light source, the wavelength of the emitted light appears A) longer. B) shorter. C) the same.

Q: As you approach a steady light source, the wavelength of the emitted light appears A) longer. B) shorter. C) the same.

Q: As a blinking light source uniformly accelerates away from you, you observe the blinks A) more and more frequently. B) less and less frequently. C) neither of these

Q: As a light source blinking at a steady rate approaches you at an increasing speed (accelerating toward you), the rate at which the blinks encounter you A) increases. B) decreases. C) remains the same.

Q: If the frequency of blinks for a light source appears to double as the light source approaches you, the frequency of blinks as it moves away from you at the same speed A) is halved. B) is doubled. C) stays the same.

Q: A light source blinks with a certain frequency in its own frame of reference, and the speed of light in that frame is c. When the light source approaches you, you observe an increase in A) both speed of light and frequency of blinking. B) speed of light, but not frequency of blinking. C) frequency of blinking, but not speed of light.

Q: A certain light source blinks once per second in its own frame of reference. As you recede from the blinking source, you observe the frequency of blinks to be A) less than 1 Hz. B) 1 Hz. C) more than 1 Hz.

Q: A light source blinks once per second in its own frame of reference. As you approach the blinking source, you observe the frequency of blinks to be A) less than 1 Hz. B) 1 Hz. C) more than 1 Hz.

Q: When a blinking light source moves relative to you, the speed of the light A) changes but the frequency of blinks remains constant. B) remains constant but the frequency of blinks can change. C) stays the same, as does the blinking frequency.

Q: When a moving spaceship emits regularly-spaced flashes of light, how frequently you see the flashes depends on the ship A) approaching you. B) receding from you. C) either of these D) none of these

Q: According to relativity theory, if a space trip finds a son or daughter biologically older than their parents, then the space trip is taken by the A) son or daughter. B) parents. C) either of these D) neither, it can't be done.

Q: Suppose you and your sister travel at different speeds in space and you note a slowing of her clock. Compared with her clock your sister will notice that your clock runs A) faster. B) slower. C) the same. D) need more information

Q: Harry takes a space voyage and returns to find his twin sister has aged more than he has. This is evidence that A) she has changed frames of reference. B) he has changed frames of reference. C) both have changed frames of reference. D) neither has changed frames of reference

Q: We are actually looking into the past when we look at A) a distant star. B) our physics book. C) actually both of these D) none of the above

Q: According to the special theory of relativity, while traveling at very high speed your pulse rate A) increases. B) decreases. C) remains unchanged.

Q: You look at the clock on the Big Ben Tower in London and it reads 12 noon. If you could hypothetically travel away from the clock at the speed of light and view it with a telescope, it would A) run slower than a clock in your vehicle. B) run faster than a clock in your vehicle. C) be frozen at 12 noon.

Q: The clock on the Big Ben Tower in London reads 12 noon. If you travel away from the clock at a very high speed and view it with a telescope, you would see A) run slower than a clock in your vehicle. B) run faster than a clock in your vehicle. C) be frozen at 12 noon.

Q: The Lorentz factor, γ, A) is always greater than 1 for any speed greater than zero. B) lets the time-dilation equation be expressed t = γ t0. C) both of these D) none of these

Q: Clocks on a spaceship moving at high speed relative to the Earth run more slowly when viewed from A) within the spaceship. B) Earth. C) both of these D) neither of these

Q: Compared to clocks in a stationary reference frame, clocks in a moving reference frame run A) slower. B) faster. C) at the same rate.

Q: The stretching out of time due to motion is called time A) stretching. B) dilation. C) contraction. D) warp. E) expansion.