Physics 7. Homework # 6
Due:
5/10
1) A log is 1m wide and 3m high when
at rest. When observed while moving at a high speed as in the drawing,


a) The height and
width of the log are contracted because of relativistic effects
b) The height of the log is
contracted but not the width
c) The width is contracted but
not the height
d) Both width and height are
unaffected
2) During
an exam the instructor observes that a student whispers the answer to a
question to his neighbor who then writes it down, and just as he does
so, another student at the opposite end of the classroom sneezes. As seen by Mary,
who is moving with respect to the classroom,
a) The time ordering of all these events depends on the state of motion Mary
b) Mary sees first the whispering
and then the writing down, but the time ordering of the sneezing and the
writing depends on her state of motion
c) Mary sees the sneezing and the
writing down simultaneously, but the time ordering of the whispering and the
writing down depends on the state of motion
d) Mary sees the same situation
as the instructor, no matter how fast she moves
3) When
Fred left on a long trip to a near-by star he was 20 years old. He clocked the
trip as taking 5 years, but his twin celebrated his 87th birthday on
the day Fred came back. How long did this trip take?(In case you are curious
his speed was 99.61% that of light)
a) The trip took exactly 5 years
b) The trip took exactly 67 years
c) The trip took the average of 5
and 67 years, that is 36 years
d)
For Fred it took 5 years, for his twin it took 67 years. These times
are not the same because time intervals depend on the state of motion of the
observer.