Question 1

Special relativity says that moving clocks run slower.

Accepted Answer

A) True 
 B)False

Question 2

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

Accepted Answer

Einstein's theory of general relativity

Question 3

Suppose we discovered radio signals coming from the star Alpha Centauri, whose distance is 4.4 light-years from us, and we sent a crew in a spacecraft to visit it. If the spacecraft used revolutionary technology allowing it to travel at a speed of 0.5 c, how long would it take the spacecraft to get to Alpha Centauri, and how long a time would the astronauts say passed during the trip? (Ignore the time it would take to accelerate the spacecraft to reach a velocity of 0.5
c.)

Accepted Answer

Traveling at a speed of 0.5 c, the time

Question 4

Muons are elementary particles that decay into other particles in about 2 microseconds. They are formed in the upper atmosphere of the Earth from high energy cosmic rays, and can be detected on the ground even though they could only travel a few hundred meters before decaying according to Newtonian physics. How does relativity explain how we can detect them on the ground? Explain both in our reference frame and in the frame of the muon.

Accepted Answer

From our reference frame, we see the muo

Question 5

In the rubber-sheet analogy for spacetime, what would you expect for objects (such as golf balls) rolling around in the presence of a massive object that is stretching the rubber sheet?

Accepted Answer

A)  Their paths would be straight if they were moving slowly enough. 
B)  Their paths would curve more the closer they come to the massive object. 
C)  Their paths would curve by the same amount no matter how close they come to the mass. 
D)  Their paths would curve towards the mass if they passed close, but bend away from the mass if they passed far from the mass. 
E)  Their paths would curve less the closer they come to the massive object. 
A)  Their paths would be straight if they were moving slowly enough. 
B)  Their paths would curve more the closer they come to the massive object. 
C)  Their paths would curve by the same amount no matter how close they come to the mass. 
D)  Their paths would curve towards the mass if they passed close, but bend away from the mass if they passed far from the mass. 
E)  Their paths would curve less the closer they come to the massive object.

Question 6

According to Einstein's relativity, which two quantities are different manifestations of the same thing?

Accepted Answer

A)  mass and gravity 
B)  light and energy 
C)  energy and mass 
D)  temperature and energy 
E)  distance and time 
A)  mass and gravity 
B)  light and energy 
C)  energy and mass 
D)  temperature and energy 
E)  distance and time

Question 7

General relativity predicts that pairs of objects with nonzero masses undergoing accelerations can produce:

Accepted Answer

A)  pulses of electromagnetic radiation 
B)  gravitational waves 
C)  high-energy particles 
D)  a slowing of clocks here on the Earth 
E)  redshifted light from the surface of the object 
A)  pulses of electromagnetic radiation 
B)  gravitational waves 
C)  high-energy particles 
D)  a slowing of clocks here on the Earth 
E)  redshifted light from the surface of the object

Question 8

What is the meaning of the equation E = mc2?

Accepted Answer

This is the famous equation relating ene

Question 9

Gravity is nothing more than a curvature in the fabric of spacetime.

Accepted Answer

A) True 
 B)False

Question 10

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 * 10 - 4 seconds before it decayed when, in fact, it lived for only 2 *10 - 6 seconds in its moving reference frame?

Accepted Answer

A)  0.05c 
B)  0.50c 
C)  0.95c 
D)  0.995c 
E)  0.99995c 
A)  0.05c 
B)  0.50c 
C)  0.95c 
D)  0.995c 
E)  0.99995c

Question 11

The equivalence principle says that:

Accepted Answer

A)  the universe is homogeneous and isotropic 
B)  being stationary in a gravitational field is the same as being in an accelerated reference frame 
C)  at any radius inside a star the outward gas pressure must balance the weight of the material on top 
D)  mass and energy are interchangeable and neither can be destroyed 
E)  gravity does not exist in space 
A)  the universe is homogeneous and isotropic 
B)  being stationary in a gravitational field is the same as being in an accelerated reference frame 
C)  at any radius inside a star the outward gas pressure must balance the weight of the material on top 
D)  mass and energy are interchangeable and neither can be destroyed 
E)  gravity does not exist in space

Question 12

The event horizon of a black hole is defined as:

Accepted Answer

A)  the point of maximum gravity 
B)  the radius of the original neutron star before it became a black hole 
C)  the radius from which shock waves course through spacetime due to the strong gravitational distortion of the black hole 
D)  the radius at which the escape speed from the black hole equals the speed of light 
E)  the radius at which the gravitational force is the same as that on the surface of the Sun 
A)  the point of maximum gravity 
B)  the radius of the original neutron star before it became a black hole 
C)  the radius from which shock waves course through spacetime due to the strong gravitational distortion of the black hole 
D)  the radius at which the escape speed from the black hole equals the speed of light 
E)  the radius at which the gravitational force is the same as that on the surface of the Sun

Question 13

If you were to design a spacecraft that could travel to the galactic center fast enough that the astronauts aboard only aged by 25 years during the trip, how fast would the spacecraft have to go? The galactic center is 25,000 light years away.

Accepted Answer

A)  0.95c 
B)  0.995c 
C)  0.99995c 
D)  0.9999995c 
E)  0.999999995c 
A)  0.95c 
B)  0.995c 
C)  0.99995c 
D)  0.9999995c 
E)  0.999999995c

Question 14

What are gravitational waves? Have they been detected?

Accepted Answer

Gravitational waves are ripples in space

Question 15

The Schwarzschild radius of a 10M $\odot$  is __________ the size of the Schwarzschild radius of a 5 M $\odot$  black hole.

Accepted Answer

A)  1/5 
B)  1/2 
C)  equal to 
D)  2 times 
E)  5 times 
A)  1/5 
B)  1/2 
C)  equal to 
D)  2 times 
E)  5 times

Question 16

Describe two possible ways to make a black hole.

Accepted Answer

Black holes can be made in supernova exp

Question 17

What would happen if mass were continually added to a 2M $\odot$  neutron star?

Accepted Answer

A)  The star's radius would increase. 
B)  The star could eventually become a black hole. 
C)  The star could erupt as a nova. 
D)  The star could exceed the Chandrasekhar limit and become a Type II supernova. 
E)  The star could eventually return to the top of the main sequence. 
A)  The star's radius would increase. 
B)  The star could eventually become a black hole. 
C)  The star could erupt as a nova. 
D)  The star could exceed the Chandrasekhar limit and become a Type II supernova. 
E)  The star could eventually return to the top of the main sequence.

Question 18

The principle of equivalence states that the gravitational mass is equal to:

Accepted Answer

A)  the mass when moving nearly the speed of light 
B)  the resistance to acceleration 
C)  the mass when near a black hole 
D)  the object's weight 
E)  the density divided by the volume 
A)  the mass when moving nearly the speed of light 
B)  the resistance to acceleration 
C)  the mass when near a black hole 
D)  the object's weight 
E)  the density divided by the volume

Question 19

A person would feel __________ as he approached the event horizon of a black hole.

Accepted Answer

A)  extremely strong tidal forces 
B)  intense heating 
C)  strong Hawking radiation 
D)  strong infrared radiation 
E)  nothing 
A)  extremely strong tidal forces 
B)  intense heating 
C)  strong Hawking radiation 
D)  strong infrared radiation 
E)  nothing

Question 20

The Earth orbits the Sun because the Sun changes space around it but not time.

Accepted Answer

A) True 
 B)False

Exam 18: Relativity and Black Holes

Special relativity says that moving clocks run slower.

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

In the rubber-sheet analogy for spacetime, what would you expect for objects (such as golf balls) rolling around in the presence of a massive object that is stretching the rubber sheet?

According to Einstein's relativity, which two quantities are different manifestations of the same thing?

General relativity predicts that pairs of objects with nonzero masses undergoing accelerations can produce:

What is the meaning of the equation E = mc2?

Gravity is nothing more than a curvature in the fabric of spacetime.

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 * 10 - 4 seconds before it decayed when, in fact, it lived for only 2 *10 - 6 seconds in its moving reference frame?

The equivalence principle says that:

The event horizon of a black hole is defined as:

If you were to design a spacecraft that could travel to the galactic center fast enough that the astronauts aboard only aged by 25 years during the trip, how fast would the spacecraft have to go? The galactic center is 25,000 light years away.

What are gravitational waves? Have they been detected?

The Schwarzschild radius of a 10M ⊙\odot⊙ is __________ the size of the Schwarzschild radius of a 5 M ⊙\odot⊙ black hole.

Describe two possible ways to make a black hole.

What would happen if mass were continually added to a 2M ⊙\odot⊙ neutron star?

The principle of equivalence states that the gravitational mass is equal to:

A person would feel __________ as he approached the event horizon of a black hole.

The Earth orbits the Sun because the Sun changes space around it but not time.

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

The Expanding Universe

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

What is the meaning of the equation E = mc²?

How fast must a muon be moving if it looks to an observer at rest that it lived for 2 * 10 ^- ⁴ seconds before it decayed when, in fact, it lived for only 2 *10 ^- ⁶ seconds in its moving reference frame?

The Schwarzschild radius of a 10M _$\odot$ is __________ the size of the Schwarzschild radius of a 5 M _$\odot$ black hole.

What would happen if mass were continually added to a 2M _$\odot$ neutron star?