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AST201-A QUESTIONS AND ANSWERS FULLY SOLVED
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Exam of 11 pages for the course Relativity at Relativity (AST201-A)
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AST201-AThe primary difference between the special theory of relativity and the general theory of
relativity is that the general theory also describes ______. - answerthe nature of gravity
Which of the following statements best describes what is "relative" in the theory of
relativity?
A. The theory says that measurements of motion make sense only when we state what
they are measured relative to.
B. The theory says that the speed of light is relative and depends on who is measuring
it.
C. The theory says that truth can never be established in any absolute sense.
D. The theory says that everything is relative. - answerA
In relativity, two people share the same reference frame only if what is true?
A. They agree on the laws of nature.
B. They are both located in the same place.
C. They are not moving relative to one another.
D. They are both located in the same place and are stationary. - answerC
You are in an airplane, traveling relative to the ground at 500 km/hr. You throw a
baseball toward the front of the plane at a speed of 50 km/hr. How fast would someone
on the ground say the baseball is moving? - answer550 km/hr
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? - answerThe ball will be stationary, floating freely in her own reference
frame.
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 ______. - answer300,000
km/s
, What do we mean by time dilation in relativity? - answerIt is the idea that time really
runs slower in reference frames moving relative to you.
You can see a clock in a spaceship moving past you at 90% of the speed of light.
According to you, how much time would pass while the clock in the spaceship ticked
through one minute? - answerMore than one minute
What do we mean by length contraction in relativity? - answerIt is the idea that if you
measure the size of an object moving relative to you, you will find that in the direction of
motion it is shorter than it would be at rest, while its size in other directions is
unchanged.
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? - answerYou will say that
Kim's time is running slow, and she will say that your time is running slow.
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 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? - answerAbout 25 years
Consider the same scenario as in a previous problem. 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? - answerShe 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.
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.) -
answerIt'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.
Which of the following is NOT true of the special theory of relativity?
A. The theory tells us that there is no such thing as absolute time or space because
measurements of time and space depend on your reference frame.
B. The special theory does not apply to situations that involve substantial acceleration
or gravity; for that, you need the general theory of relativity.
C. The theory is valid only at speeds close to the speed of light.
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