Physics 7. Homework # 7
Due:
5/17
1) What was the one peculiarity in
a) That it was valid only for
non-inertial observers
b) That it assumed instantaneous
propagation of interactions
c) That it required light to
travel at infinite speeds
d) That was inconsistent with
2) Becky
and Tom are in outer space, each in her/his own spaceship and have identical clocks.
Both their reference frames are inertial and they are moving with respect to
one another at a large speed. When Becky compares Tom’s clock to hers, she
finds it is slow. When Tom compares his clock to Becky’s, will he find it is
a) Fast, because Becky find his
clock slow
b) Slow, because in his reference
frame Becky’s clock is moving and it will slow down because of relativistic
effects
c) Synchronized, because time
flows in the same way for all inertial observers
d) Stopped
3) The
distance from Earth to Alpha Centauri (a near-by star) is about 5.4 light years
(one light year is the distance light covers in one year, or about 160 billion
km). Yuri the astronaut decides to take a trip to this star and he will travel
very fast. When he arrives will he find that
a) In his reference frame he
covered a distance smaller than 5.4 light years because of relativistic length
contraction
b) In his reference frame the
distance he traveled was also 5.4 light years
c) In his reference frame he
covered more than 5.4 light years
d) That the trip takes a very
long time, much more than 5.4 years, even if moving close to the speed of light
with respect to us.
4) What
physical principle makes atomic bombs possible?
a) The absolute nature of the
speed of light
b) The equivalence of mass and
energy
c) The absence of the ether
d) Maxwell’s theory of
electromagnetism
5) A laser is placed on top of a
hill (here on Earth) and turned on. Assume that the beam encounters no
obstacles and that there are no losses when it travels through the air, and
that the beam does not spread. Then,
a) The gravitational force pulls
the beam towards the center of the Earth
b) The gravitational force pushes
the beam away from Earth
c) The gravitational force has no
effect, for otherwise the beam would move around the Earth in an ellipse
d) The gravitational force
affects the beam as long as it is inside the atmosphere, once the beam leaves
the atmosphere behind the gravitational effects stop abruptly.