Question 1

In an observation made in 1919 demonstrating the deflection of starlight due to gravity, light rays moving near ___________ bent to a slightly different angle.

Accepted Answer

The observation made in 1919 demonstrated the deflection of starlight due to gravity. Light rays moving near the Sun bent to a slightly different angle, providing evidence for Einstein's theory of general relativity.

Question 2

An inertial force can be felt by observers

Accepted Answer

An inertial force can be felt by observers whose reference frame moves in a circle. This is known as a centrifugal force, which is an example of an inertial force. It arises due to the observer's frame of reference undergoing circular motion, and is not an actual force acting on the system.

Question 3

Two identical clocks are made. One is placed on the surface of a massive planet, and the other is placed in interstellar space. Which runs faster?

Accepted Answer

The space clock runs faster due to the effects of gravitational time dilation. According to general relativity, time passes more slowly in stronger gravitational fields, so the clock on the surface of a massive planet would run slower compared to the clock in interstellar space where the gravitational field is weaker.

Question 4

Two identical atomic clocks are made. One is placed in the foothills of the Rocky Mountains at the NIST in Boulder, Colorado, about one mile above the sea level, and the second is flown in a GPS satellite around Earth at about 17,000 mph. Which clock gets ahead of the other?

Accepted Answer

The clock in orbit gets ahead due to the effects of both special and general relativity. Special relativity predicts that moving clocks run slower, which would suggest the clock on the GPS satellite should lag. However, general relativity predicts that clocks in a stronger gravitational field (closer to Earth) run slower than those in a weaker gravitational field (further from Earth, as in the satellite). The effect of general relativity overcomes that of special relativity in this scenario, making the satellite clock run faster than the one on Earth.

Question 5

Light takes 4.3 years to travel from Alpha Centauri (the star closest to the Sun) to the Earth. If a spaceship traveling near the speed of light were to make the same trip, the time to travel this distance as measured by the astronauts would be

Accepted Answer

According to Einstein's Theory of Special Relativity, an astronaut traveling at a speed close to the speed of light would experience time dilation, which means that time would appear to pass slower for them than for someone who is stationary. Therefore, the time measured by the astronaut on the spaceship would be less than 4.3 years.

Question 6

According to the postulates of special relativity

Accepted Answer

The postulates of special relativity state that the laws of physics are the same for all observers in uniform motion relative to one another, and that the speed of light is constant for all observers regardless of their motion or the motion of the source of light. Therefore, choice B is correct. Choices A, C, and D are incorrect as they do not align with the postulates of special relativity.

Question 7

An airplane travels from east to west with a velocity 450 mi/hr relative to the Earth. At the same time the wind is blowing from west to east at 50 mi/hr. What is the speed of the plane with respect to the air?

Accepted Answer

The speed of the plane with respect to the air is the sum of its speed relative to the Earth and the speed of the wind, because they are in opposite directions. Thus, 450 mi/hr + 50 mi/hr = 500 mi/hr.

Question 8

Einstein performed thought experiments to understand the implications of the postulates of special relativity because

Accepted Answer

Einstein used thought experiments to explore the implications of special relativity because the speeds involved (close to the speed of light) are too large to easily generate in a laboratory setting, making physical experiments impractical.

Question 9

A student calculates the momentum of a body moving at a relativistic speed by multiplying the rest mass by the velocity. This gives a result for the momentum that is

Accepted Answer

At relativistic speeds, the momentum should be calculated using the relativistic momentum formula, which includes the Lorentz factor. Simply multiplying rest mass by velocity underestimates the momentum.

Question 10

Suppose Spider-Man throws a web that is 1.00 m long with a velocity of 0.8c ($\gamma$ = 5/3) with respect to the Earth. What will be the length of web as observed by J. Jonah Jameson standing on the Earth?

Accepted Answer

The length contraction formula is $ L = L_0/\gamma $. Given $ L_0 = 1.00 $ m and $ \gamma = 5/3 $, the contracted length $ L = 1.00 \times 3/5 = 0.60 $ m.

Question 11

If one could measure the exact mass of a biscuit while hot and then compare it to the exact mass of the biscuit when cold, the result would be

Accepted Answer

The answer of If one could measure the exact mass...

Question 12

A train has a rest length of 100 m. Traveling at a very high velocity, it goes through a tunnel of length 80 m. Observers located at both ends of the tunnel note that at one instant the train appears to exactly fit within the tunnel. What is the velocity of the train expressed in units of c?

Accepted Answer

Let the velocity of the train be v and the length contraction factor be γ. Then, according to the observers, the length of the train as seen from outside the tunnel would be γ×100 m and the total length of the train and the tunnel together would be (γ×100 + 80) m. However, since the train exactly fits within the tunnel at that instant, we have:
γ×100 + 80 = 100
Solving for γ, we get γ = 4/5. Therefore, the velocity of the train can be found using:
v = √(1 - γ^2) × c ≈ 0.6c (since γ is very close to 1)
So the best choice is (C).

Question 13

An object that appears green in empty space is placed near but not in a black hole. To an observer far from the black hole, the object would appear

Accepted Answer

The object would appear red due to gravitational redshift, a phenomenon where light escaping the gravitational pull of a massive object (like a black hole) loses energy and shifts to the red end of the spectrum.

Question 14

The most important conclusion to be drawn from the Michelson-Morley experiment is that

Accepted Answer

The Michelson-Morley experiment was designed to detect the existence of a luminiferous ether, which was believed to be the medium through which light waves traveled. The experiment showed that there was no detectable difference in the speed of light when measured in different directions, which led to the conclusion that light does not travel through a luminiferous ether. This discovery was a major blow to the prevailing scientific theories of the time and paved the way for the development of modern physics.

Question 15

The Flash, a comic superhero, is able to run close to the speed of light. Two people, with synchronized watches, stand several kilometers apart and time the Flash as he runs a straight course. The Flash has his own stopwatch and uses it to independently time his run. The Flash also observes the speed at which the finish line moves toward him, and upon finishing his run he calculates the length of the course by multiplying this speed by the time on his stopwatch. Who measures (I) the Flash's proper time for the race, and who measures (II) the rest or proper length for the race?

Accepted Answer

The Flash measures his own proper time because he is in the same inertial frame as his stopwatch. The two people, being stationary with respect to the race course, measure its proper length.

Question 16

An object with a nonzero rest mass moving at the speed of light would have

Accepted Answer

Objects with nonzero rest mass cannot reach the speed of light within the framework of relativity. However, theoretically, as an object with mass approaches the speed of light, its relativistic mass increases without bound, appearing to become infinite.

Question 17

A starship "Alpha" travels at 0.8c past an identical starship, "Beta," which is at rest. Both an engineer on the "Alpha" and a scientist on the "Beta" measure the length of the other ship as it passes by. Who measures the longer length?

Accepted Answer

The answer of A starship "Alpha" travels at 0.8c past...

Question 18

One of two identical twins becomes an astronaut, while the other becomes a real estate broker. The astronaut embarks on high-speed space travel and is gone for several years. Upon the astronaut's return, the two twins reunite and compare their physical appearances. The result will be that

Accepted Answer

According to the theory of relativity, time dilation occurs when an object moves at high speeds. This means that time for the astronaut traveling at high speeds will appear to pass slower compared to the time for the real estate broker who stayed on Earth. Therefore, the astronaut will have aged less than the real estate broker when they reunite.

Question 19

Starship "Alpha" is traveling at 0.8c ($\gamma$ = 5/3) with respect to the identical starship "Beta." Each starship has rest length 10,000 m. The ship's engineer aboard the "Beta" measures the length of the "Alpha" as it passes by his window. What result should he get?

Accepted Answer

The length contraction formula in special relativity is $L = L_0/\gamma$, where $L_0$ is the rest length and $\gamma$ is the Lorentz factor. Given $\gamma = 5/3$ and $L_0 = 10,000$ m, the observed length $L$ is $10,000 \times 3/5 = 6,000$ m.

Question 20

The purpose of the Michelson-Morley experiment was to

Accepted Answer

The Michelson-Morley experiment was designed to detect the possible motion of the Earth relative to the ether. At the time, it was believed that light waves traveled through an "ether" which filled all of space. The experiment aimed to detect the motion of the Earth through this supposed ether by measuring the speed of light in different directions. However, the experiment failed to detect any ether wind and led to the formulation of Einstein's theory of relativity.

Quiz 20: Relativity

In an observation made in 1919 demonstrating the deflection of starlight due to gravity, light rays moving near ___________ bent to a slightly different angle.

An inertial force can be felt by observers

Two identical clocks are made. One is placed on the surface of a massive planet, and the other is placed in interstellar space. Which runs faster?

Two identical atomic clocks are made. One is placed in the foothills of the Rocky Mountains at the NIST in Boulder, Colorado, about one mile above the sea level, and the second is flown in a GPS satellite around Earth at about 17,000 mph. Which clock gets ahead of the other?

Light takes 4.3 years to travel from Alpha Centauri (the star closest to the Sun) to the Earth. If a spaceship traveling near the speed of light were to make the same trip, the time to travel this distance as measured by the astronauts would be

According to the postulates of special relativity

An airplane travels from east to west with a velocity 450 mi/hr relative to the Earth. At the same time the wind is blowing from west to east at 50 mi/hr. What is the speed of the plane with respect to the air?

Einstein performed thought experiments to understand the implications of the postulates of special relativity because

A student calculates the momentum of a body moving at a relativistic speed by multiplying the rest mass by the velocity. This gives a result for the momentum that is

Suppose Spider-Man throws a web that is 1.00 m long with a velocity of 0.8c ( $\gamma$ = 5/3) with respect to the Earth. What will be the length of web as observed by J. Jonah Jameson standing on the Earth?

If one could measure the exact mass of a biscuit while hot and then compare it to the exact mass of the biscuit when cold, the result would be

A train has a rest length of 100 m. Traveling at a very high velocity, it goes through a tunnel of length 80 m. Observers located at both ends of the tunnel note that at one instant the train appears to exactly fit within the tunnel. What is the velocity of the train expressed in units of c?

An object that appears green in empty space is placed near but not in a black hole. To an observer far from the black hole, the object would appear

The most important conclusion to be drawn from the Michelson-Morley experiment is that

An object with a nonzero rest mass moving at the speed of light would have

A starship "Alpha" travels at 0.8c past an identical starship, "Beta," which is at rest. Both an engineer on the "Alpha" and a scientist on the "Beta" measure the length of the other ship as it passes by. Who measures the longer length?

One of two identical twins becomes an astronaut, while the other becomes a real estate broker. The astronaut embarks on high-speed space travel and is gone for several years. Upon the astronaut's return, the two twins reunite and compare their physical appearances. The result will be that

Starship "Alpha" is traveling at 0.8c ( $\gamma$ = 5/3) with respect to the identical starship "Beta." Each starship has rest length 10,000 m. The ship's engineer aboard the "Beta" measures the length of the "Alpha" as it passes by his window. What result should he get?

The purpose of the Michelson-Morley experiment was to

Quiz 20: Relativity

In an observation made in 1919 demonstrating the deflection of starlight due to gravity, light rays moving near ___________ bent to a slightly different angle.

An inertial force can be felt by observers

Two identical clocks are made. One is placed on the surface of a massive planet, and the other is placed in interstellar space. Which runs faster?

Two identical atomic clocks are made. One is placed in the foothills of the Rocky Mountains at the NIST in Boulder, Colorado, about one mile above the sea level, and the second is flown in a GPS satellite around Earth at about 17,000 mph. Which clock gets ahead of the other?

Light takes 4.3 years to travel from Alpha Centauri (the star closest to the Sun) to the Earth. If a spaceship traveling near the speed of light were to make the same trip, the time to travel this distance as measured by the astronauts would be

According to the postulates of special relativity

An airplane travels from east to west with a velocity 450 mi/hr relative to the Earth. At the same time the wind is blowing from west to east at 50 mi/hr. What is the speed of the plane with respect to the air?

Einstein performed thought experiments to understand the implications of the postulates of special relativity because

A student calculates the momentum of a body moving at a relativistic speed by multiplying the rest mass by the velocity. This gives a result for the momentum that is

Suppose Spider-Man throws a web that is 1.00 m long with a velocity of 0.8c ( γ\gammaγ = 5/3) with respect to the Earth. What will be the length of web as observed by J. Jonah Jameson standing on the Earth?

If one could measure the exact mass of a biscuit while hot and then compare it to the exact mass of the biscuit when cold, the result would be

A train has a rest length of 100 m. Traveling at a very high velocity, it goes through a tunnel of length 80 m. Observers located at both ends of the tunnel note that at one instant the train appears to exactly fit within the tunnel. What is the velocity of the train expressed in units of c?

An object that appears green in empty space is placed near but not in a black hole. To an observer far from the black hole, the object would appear

The most important conclusion to be drawn from the Michelson-Morley experiment is that

An object with a nonzero rest mass moving at the speed of light would have

A starship "Alpha" travels at 0.8c past an identical starship, "Beta," which is at rest. Both an engineer on the "Alpha" and a scientist on the "Beta" measure the length of the other ship as it passes by. Who measures the longer length?

One of two identical twins becomes an astronaut, while the other becomes a real estate broker. The astronaut embarks on high-speed space travel and is gone for several years. Upon the astronaut's return, the two twins reunite and compare their physical appearances. The result will be that

Starship "Alpha" is traveling at 0.8c ( γ\gammaγ = 5/3) with respect to the identical starship "Beta." Each starship has rest length 10,000 m. The ship's engineer aboard the "Beta" measures the length of the "Alpha" as it passes by his window. What result should he get?

The purpose of the Michelson-Morley experiment was to

Suppose Spider-Man throws a web that is 1.00 m long with a velocity of 0.8c ( $\gamma$ = 5/3) with respect to the Earth. What will be the length of web as observed by J. Jonah Jameson standing on the Earth?

Starship "Alpha" is traveling at 0.8c ( $\gamma$ = 5/3) with respect to the identical starship "Beta." Each starship has rest length 10,000 m. The ship's engineer aboard the "Beta" measures the length of the "Alpha" as it passes by his window. What result should he get?