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C
HAPTER
26
Quick Quizzes
1.
(b). Assuming that your onduty time was kept on Earth, you will be pleasantly surprised
with a
large
paycheck. Less time will have passed for you in your frame of reference than
for your employer back on Earth.
2.
The answers to both of these questions is
no
. Both your clothing and your sleeping cabin
are at rest in your reference frame, thus, they will have their proper length. There will be
no change in measured lengths of objects within your spacecraft. Another observer, on a
spacecraft traveling at a high speed relative to yours, will measure you as thinner (if your
body is oriented in a direction perpendicular to the direction of motion relative to him) or
will claim that you are able to fit into a shorter sleeping cabin (if your body is oriented in a
direction parallel to your direction of travel relative to the other observer).
3.
(a), (e). The outgoing rocket will appear to have a
shorter
length and a
slower
clock. The
answers are the same for the incoming rocket. Length contraction and time dilation
depend only on the magnitude of the relative velocity, not on the direction.
4.
(a) False
(b) False
(c) True
(d) False
A reflected photon does exert a force on the surface. Although a photon has zero mass, a
photon does carry momentum. When it reflects from a surface, there is a change in the
momentum, just like the change in momentum of a ball bouncing off a wall. According to
the momentum interpretation of Newton’s second law, a change in momentum results in
a force on the surface. This concept is used in theoretical studies of space sailing. These
studies propose building nonpowered spacecraft with huge reflective sails oriented
perpendicularly to the rays from the Sun. The large number of photons from the Sun
reflecting from the surface of the sail will exert a force which, although small, will provide
a continuous acceleration. This would allow the spacecraft to travel to other planets
without fuel.
5.
(a). The downstairs clock runs more slowly because it is closer to the Earth and hence
experiences a stronger gravitational field than the upstairs clock does.
327
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Problem Solutions
26.1
(a) As the plane flies from
O
to
B
along path I,
ground
ai
rw
i
nd
=
+
vv
v
gives
mm
100
20.0
120
ss
v
=+ =
m
s
, and
3
200
10 m
120 m s
OB
L
t
v
×
==
=
3
1.67
10 s
×
v
ground
v
wind
v
air
For the plane following path II from
O
to
A
,
i
=
+
v
with
perpendicular to each other. The Pythagorean theorem then yields
and
wind
22
98.0
i
v
⎛⎞
⎛ ⎞
=−=
−
=
⎜⎟
⎜ ⎟
⎝⎠
⎝ ⎠
m
s
,
and
3
98.0 m s
OA
L
t
v
×
=
3
2.04
×
v
ground
v
wind
v
air
(b) For the return flight along path I,
i
=
+
v
gives
80.0
v
=− =
m
s
,
so
3
80.0 m s
BO
L
t
v
×
=
3
2.50
×
v
ground
v
wind
v
air
As the plane flies from
A
to
O
along path II,
are again
perpendicular to each other. The Pythagorean theorem gives
w ind
m
s
i
nd
v
,
and
AO
L
t
v
3
×
v
ground
v
wind
v
air
328
CHAPTER 26
(c) The total times of flight are
,
and
33
I
1.67
10
m2
.
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This homework help was uploaded on 03/21/2008 for the course PY 211 / 212 taught by Professor Chilton during the Spring '08 term at N.C. State.
 Spring '08
 Chilton

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