Astronomy ChS2
Each of the following lists two statements. Which two are the basic premises for the special theory of relativity?
1. The laws of nature are the same for everyone.2. The speed of light is the same for everyone
The measured value of the speed of light is about 300,000 km/s. Suppose a futuristic space train is traveling at 200,000 km/s with its headlights on. If you could measure the speed of the light from the headlights, you would find it to be ______.
300,000 km/s
Carol is going away from you at 75 km/hr, and Sam is going in the opposite direction away from you at 90 km/hr. According to Carol, how fast is Sam going?
Carol sees Sam going away from her at 165 km/hr.
What does the famous formula E=mc2 have to do with special relativity?
It is a direct consequence of the theory.
What provides the strongest evidence that everyone always measures the same speed of light?
Precise measurements of the speed of light under different circumstances
You and Mae are in free-float frames. Mae has just passed you, traveling at a speed of 60 km/hr. You throw a ball toward her at a speed of 60 km/hr. What will Mae see the ball doing?
The ball will be stationary, floating freely in her own reference frame
Which of the following must be true of a person who shares the same reference frame as you?
The person must not be moving relative to you
Sue is traveling toward you at 90 km/hr. She throws a baseball that, according to her, is going at 90 km/hr in the opposite direction. What do you see the ball doing?
You see the ball remaining stationary.
Shawn is traveling away from you at a speed of 120 km/hr. He throws a baseball that, according to him, is going at 100 km/hr in your direction. What do you see the ball doing?
You see the ball traveling away from you at 20 km/hr.
Kim is in a spaceship moving past you at half the speed of light. Which of the following correctly describes how you will perceive each other's time?
You will say that Kim's time is running slow, and she will say that your time is running slow.
You are racing away from Earth in a super spaceship in which you can continually increase your speed. Which of the following best explains how people on Earth will perceive your speed?
You will see any beam of light from Earth coming toward you at the speed of light, which means it will catch you. Thus, the people on Earth must conclude that you are going slower than the speed of light.
If you observe people moving by you at very high speed, you will say that their time runs slowly, their lengths are contracted in the direction of motion, and their masses are increased from their rest masses. What will they say about you?
Your time runs slowly, your length is contracted in the direction of motion, and your mass is increased from your rest mass.
Suppose you had a spaceship so fast that you could make a roundtrip journey of 1 million light-years (in Earth's reference frame) in just 50 years of ship time. If you left in the year 2030, you would return to Earth
a million years from now
Which of the following statements best describes what is "relative" in the theory of relativity?
The theory says that measurements of motion make sense only when we state what they are measured relative to.
A super train is moving along a track at a speed close to the speed of light. You are watching the train from the ground. You observe lightning to strike in two places along the track, a mile apart, at precisely the same time. What would someone on the train say?
The two bolts of lightning struck at different times, and they struck at places that are less than a mile apart.
A spaceship is moving past us at a speed close to the speed of light.How would we view time (clocks) on the spaceship as it goes by?
Their clocks are going slower than ours.
Twin sisters, Gwen and Jackie, were both 20 years old in the year 2000. Jackie took off on a round trip to Vega, 25 light-years away. She traveled at an average speed very close to the speed of light—say, 0.9999c. According to Gwen back on Earth, about how long does it take Jackie to reach Vega?
about 25 years
Two twin sisters, Gwen and Jackie, are both 20 years old in the year 2020. Jackie takes off on a round-trip to Vega, 25 light-years away. She travels at an average speed very close to the speed of light—say, 0.9999c. According to Gwen back on Earth, about how long does it take Jackie to reach Vega?
about 25 years
Al is moving by you at a very high speed (close to the speed of light). You get out a clock and measure 10 seconds going by. If you also watch a clock in Al's ship, how much time will you see it record during your 10 seconds?
al's clock will record less than 10 seconds
According to the authors of the text, the theory of relativity
does not violate our common sense.
If you see Al going to your left at exactly 0.99c and Bob going to your right at exactly 0.99c, Al will say that Bob is
going away from her faster than 0.99c, but slower than c
Carla is traveling past you at a speed close to the speed of light. According to you, how much time passes for Carla while 1 minute passes for you?
less than 1 minute
Carla is traveling past you at a speed close to the speed of light. According to her, how much time passes for you while 1 minute passes for her?
less than one minute
A subatomic particle that normally decays in 1 microsecond is created in a particle accelerator and is traveling at close to the speed of light. If you measure its lifetime in that case, you'll find that it is
more than 1 microsecond
You can see a clock in a spaceship moving past you at 90 percent of the speed of light. According to you, how much time would pass while the clock in the spaceship ticked through one minute?
more than one minute
A spaceship is moving past us at a speed close to the speed of light. How would the passengers on the spaceship view our clocks?
our clocks going slow
A spaceship is headed toward Alpha Centauri at 0.999c. According to us, the distance to Alpha Centauri is about 4 light-years. How far away is Alpha Centauri according to the travelers in the ship?
quite a bit less than 4 light years
The primary difference between the special theory of relativity and the general theory of relativity is that the general theory also describes ______.
the nature of gravity
Which of the following is not relative in the special theory of relativity?
the speed of light
In relativity, two people share the same frame of reference only if
they are not moving relative to each other
In relativity, two people share the same reference frame only if what is true?
they are not moving relative to each other
Bob is coming toward you at a speed of 75 km/hr. You throw a baseball in his direction at 75 km/hr. What does he see the ball doing?
He sees the ball coming at him at 150 km/hr.
You and Al are both floating freely in your spaceships. Suppose Al is moving away from you at 85 km/hr. You throw a ball in his direction at a speed of 75 km/hr. According to Al, which of the following is going on?
He sees you moving away from him at 85 km/hr and the ball moving away from him at 10 km/hr.
A man is moving by you at a speed close to the speed of light. Which of the following correctly summarizes the effects you would notice on his mass, size, and time?
His mass would be increased from its value at rest, his length would be decreased from its rest value but only in the direction in which he is moving, and his time would be running slower than yours.
Again consider two twin sisters, Gwen and Jackie, who are both 20 years old in the year 2020. This time, assume that Jackie makes the round-trip to Vega, which is 25 light-years away, at an average speed of 0.9999c. Which of the following correctly describes the situation when Jackie returns to Earth? (Ages in this problem refer to biological ages—that is, how much time has passed for each sister since she was born.)
It's the year 2070. Gwen (who stayed home) is 70 years old, but Jackie is only a little older than her age of 20 when she left.
A spaceship is moving past us at a speed close to the speed of light.If we could measure the mass of the spaceship as it goes by, what would it be?
Its mass is greater than its rest mass.
Which of the following is not a prediction made by the theory of relativity?
Observers in different reference frames may disagree about the basic laws of nature.
Two twin sisters, Gwen and Jackie, are both 20 years old in the year 2020. Jackie takes off on a round-trip to Vega, 25 light-years away. She travels at an average speed of 0.9999c. Which of the following best describes the situation according to Jackie?
She stays still, while Earth rushes away from her at 0.9999c and Vega rushes toward her at 0.9999c. She sees the distance from Earth to Vega shortened considerably from 25 light-years, and therefore it takes far less than 25 years for Vega to reach her.
Which of the following best describes why your rocket could never reach the speed of light?
The absoluteness of the speed of light means you could never keep up with the light coming from you and your rocket.