### sp_re_1

```The speed of the ambulance is 60 km/h and the car is stationary. What is the
speed of the ambulance as measured by a person in the car?
vA
60 km/h
0 km/h
> 60 km/h
< 60 km/h
km
60
<
>
60
km
km
/h
0%
/h
0%
/h
0%
0
km
/h
0%
60
1.
2.
3.
4.
1
The ambulance is stationary and the car is travelling at 60 km/h. What is the
speed of the ambulance as measured by a person in the car?
vC
60 km/h
0 km/h
> 60 km/h
< 60 km/h
km
60
<
>
60
km
km
/h
0%
/h
0%
/h
0%
0
km
/h
0%
60
1.
2.
3.
4.
2
The speed of sound in still air is 340 m/s. The speed of the ambulance is 60 km/h and
the car is stationary. What speed of sound does a person in the car measure?
vA
340 km/h
0 km/h
> 340 km/h
< 340 km/h
km
34
0
<
>
34
0
km
km
/h
0%
/h
0%
/h
0%
0
km
/h
0%
34
0
1.
2.
3.
4.
3
The speed of sound in still air is 340 m/s. The ambulance is stationary and the car is
moving at 60 km/h. What speed of sound does a person in the car measure?
vc
340 km/h
0 km/h
> 340 km/h
< 340 km/h
km
34
0
<
>
34
0
km
km
/h
0%
/h
0%
/h
0%
0
km
/h
0%
34
0
1.
2.
3.
4.
4
The speed of light is c. The speed of the ambulance is c/2 and the car is
stationary. What speed of light does a person in the car measure?
vA
c
0%
c
0%
<
0%
>
0%
0
c
0
>c
<c
c
1.
2.
3.
4.
5
The speed of light is c. The ambulance is stationary and the car is moving at
c/2. What speed of light does a person in the car measure?
vC
c
0%
c
0%
<
0%
>
0%
0
c
0
>c
<c
c
1.
2.
3.
4.
6
If you were traveling with respect to the stars close to the
speed of light, you could detect it because
You would shrink
… all of the above
You could never tell your
speed by changes in you
0% 0% 0% 0% 0%
Yo
ur
m
as
s
Yo
w
ou
ur
ld
he
in
ar
c.
tw
..
ou
ld
sl
Yo
o.
u
..
w
ou
ld
…
sh
al
ri n
l
Yo
of
k
u
th
co
e
ul
ab
d
ov
ne
e
ve
rt
el
l.
..
1.
2.
3.
4.
5.
7
A spear 10 m long is thrown at a relativistic speed through a pipe that is
10 m long. Both the dimensions are measured when each is at rest.
When the spear passes through the pipe, which of the following
statements best describes what is observed?
de
pe
n
d.
..
s.
..
eq
ua
lly
An
y
of
t
he
se
,
.
t..
k
so
sh
rin
Bo
th
Any of these, depending on the
motion of the observer.
sh
rin
ks
4.
0% 0% 0% 0%
so
...
Both shrink equally so that the pipe
just covers the spear at some instant.
pi
pe
3.
sh
rin
ks
The pipe shrinks so that the spear
extends from both ends at some
instant.
Th
e
2.
sp
ea
r
The spear shrinks so that the pipe
completely covers it at some instant.
Th
e
1.
8
According to observes on Earth, it takes 2 years for a
rocket to travel to a nearby star . According to observes on
the rocket, what time has passed?. The speed of the rocket
is v and its Lorentz factor is
 
1
v2
1 2
c
v
1. 2  years
2. 2 /  years
3. 2 years
9
When the rocket arrives at the star, what time interval do
observers on the rocket measure for a clock located on the
Earth.
v
1.
2.
3.
4.
2 years
2 /  years
2 / 2 years
2  years
10
A rocket leaves Earth and travels to a nearby star at speed v
(corresponding to a Lorentz factor  = 3) relative to observes on Earth.
According to clocks on the rocket, the journey takes 2 years. If the
Earth and the star are in the same rest frame (clocks are synchronized)
what do clocks on the star read when the rocket arrives?
v
0%
ye
ar
s
ye
ar
s
0%
2
ye
ar
s
0%
2/
3
6 years
2 years
2/3 years
6
1.
2.
3.
11
Dr Chris is standing near the middle of a falling board. Dr Chris said
that the two ends of the board hit the ground at the same time and
therefore must be horizontal. But Prof Pat (who is running past the
falling board at near the speed of light) said that the end B hit the
ground first, before the other end A and therefore the board was tilted
towards the right.
Dr Chris
0%
he
Fa
ls
e:
t
Prof Pat
bo
ar
d
bo
ar
d
is
ca
n
n.
.
ho
...
0%
he
2.
True: the board is horizontal for one
observer and tilted for another observer.
False: the board can not be horizontal
and tilted at the same time.
Tr
ue
:t
1.
12
c/2
f of r: fast train (S’)
Prof Pat
A’
O’
B’
A
O
B
f of r: ground (S)
Dr Chris
AO = OB
A’O’ = O’B’
According to Prof Pat at O’ all the train clocks (A’ O’ B’) are synchronised and all
ground clocks (A O B) are synchronised. Dr Chris knows she is midway between A
& B locations. Lightning strikes each end of the train and the ground together in 2
separate events A/A’ and B/B’.
Dr Chris at O receives the flashes from A & B at the same time when the flashes
happen and works out that her clock read 10 am when the flashes happened.
When Prof Pat’s clock reads 10 am, she is exactly level with Dr Chris whose clock
13
What is the time on the ground clock A
when the lightning strikes?
1. before 10 am
2. 10 am
3. after 10 am
10
0%
am
am
0%
af
te
r1
0
be
fo
re
10
am
0%
14
What is the time on the ground clock B
when the lightning strikes?
1. before 10 am
2. 10 am
3. after 10 am
10
0%
am
am
0%
af
te
r1
0
be
fo
re
10
am
0%
15
What is the time on the train clock A’ when
the lightning strikes?
1. before 10 am
2. 10 am
3. after 10 am
10
0%
am
am
0%
af
te
r1
0
be
fo
re
10
am
0%
16
What is the time on the train clock B’ when
the lightning strikes?
1. before 10 am
2. 10 am
3. after 10 am
10
0%
am
am
0%
af
te
r1
0
be
fo
re
10
am
0%
17
A comet is chasing a spacecraft. Let v be the speed of, p the
momentum and K the kinetic energy of the comet as perceived by the
astronaut when it hits the spacecraft. In what way would increasing the
speed of the spacecraft alter the astronaut’s perceived values of v, p
and K?
no
tc
ha
ng
w
ill
e.
..
v,
al
l
p
de
w
cr
ill
ea
de
se
cr
v,
.
ea
K
se
w
ill
,K
de
w
cr
K,
...
ea
p
se
w
ill
,p
de
w
cr
...
ea
se
,v
w
...
ill
v,
p,
K
5.
0% 0% 0% 0% 0%
w
4.
v, p, K will not change at all.
v, p, K will all decrease.
v, p will decrease, K will not
change.
v, K will decrease, p will not
change.
K, p will decrease, v will not
change.
v,
p,
K
1.
2.
3.
18
A rocket ship in space emits brief flashes of light from its beacon at a
steady rate of 1 flash every 6 min rocket time. These flashes are
observed on a distance planet. If the rocket ship approaches the planet
at near light speed, observes will see the flashes at intervals
0%
6
6
m
in
m
in
0%
th
an
th
an
6
m
in
0%
m
or
e
less than 6 min
6 min
more than 6 min
le
ss
1.
2.
3.
19
A rocket ship that emits flashes of light every 6 min travels between
two planets, A and B. It travels away from A and towards B. If the
flashes are seen at 3 min intervals on B, then on planet A the flashes
are seen at
in
m
12
m
0%
in
te
rv
al
s
in
te
rv
al
s
0%
in
in
te
rv
al
s
0%
in
m
6
m
in
in
te
rv
al
s
0%
9
3 min intervals
6 min intervals
9 min intervals
12 min intervals
3
1.
2.
3.
4.
20
Our rocket ship departs from the Earth at noon & travels at the same
near light speed for 1 hour rocket time. During this hour it emits a flash
every 6 min, 10 in all. An Earth observer sees these flashes at 12 min
intervals. When the 10th flash is received on Earth, clocks on Earth read
o’
cl
oc
k
0%
2:
30
2:
00
1:
30
0%
o’
cl
oc
k
0%
o’
cl
oc
k
0%
o’
cl
oc
k
1:00 o’clock
1:30 o’clock
2:00 o’clock
2:30 o’clock
1:
00
1.
2.
3.
4.
21
Our rocket ship is able to abruptly turn around when it emits its 10th
flash and then returns to Earth at the same near light speed. It
continues sending flashes every 6 min and emits 10 flashes in its hour
of return. The rocket ship’s clock reads 2:00 o’clock when it gets back
to Earth. What time will a clock on Earth read?
0%
o’
cl
oc
k
o’
cl
oc
k
0%
2:
30
2:
00
o’
cl
oc
k
0%
3:
00
also 2:00 o’clock
2:30 o’clock
3:00 o’clock
al
so
1.
2.
3.
22
Suppose an atomic bomb was exploded in a box that was strong
enough to contain all the energy released by the bomb. After the
explosion the box would weight
0%
di
d
th
e.
..
be
...
0%
Th
e
sa
m
e
as
it
be
fo
re
th
an
The same as it did before the
explosion
ex
p.
..
3.
Le
ss
Less than before the explosion
be
fo
re
2.
th
an
More than before explosion
M
or
e
1.
0%
23
The celebrated equation E = m c2 or m = E / c2 tells us how much mass
loss m must be suffered by a nuclear reactor in order to generate a
given amount of energy E. Which of the following statements is
correct?
0%
eq
ua
t
Th
e
e
E
=
io
n
m
c2
ap
pl
ie
s
or
..
..
0%
sa
m
2.
The same E = m c2 or m = E / c2 also
tells us how much mass loss m must
be suffered by a flashlight battery
when the flashlight puts out a given
amount of energy E.
The equation applies to nuclear
energy in a reactor, E= m c2 but not
to chemical energy in a battery.
Th
e
1.
24
Consider a motor bike powered with powerful electric batteries and an
electric trolley car that are each driven near light speed. Measurements
of each from our rest frame will indicate an increase in the mass of
0%
ne
ith
er
y
0%
bo
th
0%
ca
r
0%
tro
lle
motor bike
trolley car
both
neither
m
ot
or
bi
ke
1.
2.
3.
4.
25
```