Transcript baryon number - Uplift Education

1.
An object falls freely from rest through a vertical distance of 44.0 m in a time
of 3.0 s. What value should be quoted for the acceleration of free-fall?
A. 9.778 m s-2
B. 9.780 m s-2
C. 9.78 m s-2
D. 9.8 m s-2
D.
Multiplication or division:
(3sig.fig.)x(2sig.fig) = 2sig.fig
(3sig.fig.)/(2sig.fig) = 2sig.fig
2. What is the order of magnitude for the frequency of visible light?
A. 10–15 Hz
Either you know visible light
frequency range, or you know
visible light wavelength range:
B. 10–7 Hz
C. 109 Hz
D. 1015 Hz
D.
400 nm → 0.75x1015 Hz
700 nm → 0.43x1015 Hz
and then use 𝑐 =f
3. A woman walks due north at 1 m s–1 before turning through an angle of 900 to
travel due east without any change in speed. What is the change, if any, of her
velocity?
A. No change
𝑣2
B. 1ms–1 to the west
C.
2 ms–1 to the north east
D.
2 ms–1 to the south east
𝑣1
D.
∆𝑣 = 𝑣2 − 𝑣1 = 𝑣2 + (−𝑣1 )
𝑣2
∆𝑣
−𝑣1
5. A parachutist jumps out of an aircraft and falls freely for a short time,
before opening his parachute. Which graph shows the variation of the
acceleration a with time t of the parachutist from the time he leaves the
aircraft until after the parachute is completely open?
A.
B.
B.
C.
D.
Before the parachute opens
1. When the skydiver jumps out of the
plane he accelerates due to the force of
gravity pulling him down.
2. As he speeds up the upwards air
resistance force increases. He carries on
accelerating as long as the air resistance is
less than his weight.
3. Eventually, he reaches his terminal
speed when the air resistance and weight
become equal.
After the parachute opens
4. When the parachute opens it has a large surface area which increases the air resistance. The force of air
resistance becomes much, much greater than the force of gravity. The net force on the descending skydiver
now has an acceleration that points upward - negative acceleration or deceleration. Gradient becomes strongly
negative when the parachute is opened. This causes a rapid decrease in the skydiver's velocity.
5. As the parachutist slows down, his air resistance gets less until eventually it equals the downward force of
gravity on him (his weight). Once again the two forces are equal and he falls at terminal speed. This time it's a
much slower terminal speed than before.
B.
𝑚𝑣𝑓
_ 𝑚𝑣𝑖
=
𝑚𝑣𝑓
+
_𝑚𝑣𝑖
=
Or one can decompose both vectors into components (easier)
1. Horizontal components will be the same so result of subtraction is zero.
2. Final vertical component – initial vertical component is equal to 2×(final vertical component)
D.
As the block is pulled with greater and greater force, but still doesn’t
move, form Newton’s first law it is obvious that static frictional force
increases. It is maximum at the moment, when the block starts to move:
𝑚𝑎𝑥
𝑠𝑡𝑎𝑡𝑖𝑐 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑓𝑜𝑟𝑐𝑒: 𝐹𝑓𝑟 ≤ 𝜇𝑠 𝐹𝑛 → 𝐹𝑓𝑟
= 𝜇𝑠 𝐹𝑛
Once the block starts to move, kinetic friction takes over. It is
constant force (𝐹𝑓𝑟 = 𝜇𝑘 𝐹𝑛 , but 𝜇𝑘 > 𝜇𝑠 )
8. The pound is a unit of mass equivalent to 0.454 kg. It is used in a limited number of
countries but is rarely used by modern scientists. Which statement is correct?
A. Scientists cannot be sure that all other scientists will be able to work in pounds.
B. The pound cannot be defined precisely enough to be used.
C. The pound is too large a unit to be used for most masses.
D. The pound cannot be divided into metric portions.
Everything can be converted into metric system. Just divide by 10, then again by ten…..
A.
D.
𝑀 + 𝑚 𝑣 = 𝑀𝑉
→ 𝑉=
𝑀+𝑚
𝑣
𝑀
C.
𝑐=
𝑒𝑛𝑒𝑟𝑔𝑦 𝑝𝑜𝑤𝑒𝑟 ∙ 𝑡𝑖𝑚𝑒 12 (200 − 0)
200
=
=
×
= 60
= 2000 𝐽 𝑘𝑔−1 𝐾 −1
𝑚 ∙ ∆𝜃
𝑚 ∙ ∆𝜃
0.2 (26 − 20)
6
B.
C.
It is not in SL curriculum – but one never knows.
In the case of changing P(V), work is the area
bellow graph p(V):
13. The diagram shows a simple pendulum undergoing simple harmonic motion
between positions X and Z. Y is the rest position of the pendulum.
𝐹 = −𝑚𝑔 𝑠𝑖𝑛𝜃
Which describes the magnitude of linear acceleration
and linear speed for the pendulum bob?
v=0
v=0
v = vmax
𝑎 = 𝑎𝑚𝑎𝑥 →
𝐹 = 𝐹𝑚𝑎𝑥 →
A.
B.
C.
D.
Linear acceleration
zero at Y
maximum at X and Z
maximum at X and Z
zero at X and Z
Linear speed
zero at Y
B.
zero at X and Z
maximum at X and Z
maximum at X and Z
𝑎=0
𝐹=0
𝑎 = 𝑎𝑚𝑎𝑥 ←
𝐹 = 𝐹𝑚𝑎𝑥 ←
linear means along the arch
14. Some of the properties that can be demonstrated using waves are
I. refraction
II. polarization
III. diffraction.
Which properties can be demonstrated using sound waves?
A. I and II only
B. I and III only B.
C. II only
D. III only
polarization happens only with
transverse waves, and sound is
longitudinal wave
15. The amplitude of a wave at a certain distance for a source is A and its
intensity is I. At this position the amplitude increases to 4A. What is the
intensity of the wave?
A. I
B. 2I
𝐼=
C. 4I
D. 16I
D.
𝑃
4𝜋𝑑 2
power is 𝑒𝑛𝑒𝑟𝑔𝑦 × 𝑡𝑖𝑚𝑒.
Energy is proportional to amplitude squared.
Intensity is proportional to amplitude squared.
16. Light travels with speed v and wavelength λ in a medium of refractive index n1 .
The light then enters a second medium of refractive index n2 . What is the speed and
the wavelength of the wave in the second medium?
A.
𝑐
𝑣
2. frequency depends on the source only and
doesn’t change when wave changes medium
1. 𝑛 =
𝑐
𝑣1
𝑛1
𝑛1 𝑛2
= 𝑐 =
→ 𝑣2 = 𝑣1
𝑣2
𝑛1
𝑛2
𝑛2
𝑣1
1 𝑓
𝑛2
𝑛2
=
=
→ 2 = 1
𝑣2
2 𝑓 𝑛1
𝑛1
17. The diagram shows two pipes of equal length. Pipe X is open at both ends and pipe
Y is closed at one end.
Which is correct about the harmonics that each pipe can produce?
Pipe X
Pipe Y
A.
all harmonics
all harmonics
B.
all harmonics
odd harmonics only B.
C.
odd harmonics only all harmonics
D.
odd harmonics only odd harmonics only
18. Two wires of different diameters are made from the same metal. The wires are connected
in series with a cell. Which quantity will be smaller in the thicker wire?
A. The current
B. The drift velocity of the electrons B.
C. The number of free electrons per unit volume
D. The number of free electrons passing through any cross-section of the wire per second
𝑅=𝜌
𝐿
𝐴
I = nAvq
In conclusion, we could say that a short fat
cold wire makes the best conductor.
If you double the length of a wire, you will
double the resistance of the wire.
If you double the cross sectional area of a
wire you will cut its resistance in half.
and this option is not a choice
▪ Imagine a cylindrical conductor that is carrying
an electric current I.
▪ The cross-sectional area of the conductor is A
▪ It contains charge carriers each with charge q.
▪ n is charge carriers density
▪ We assume that each carrier has a speed v
in series means:
the same current is passing through both of them
the same charge on charge carriers
so the drift speed must be different – more resistance in thinner wire.
19. A heating coil is connected to a battery of electromotive force (emf) 10 V and
negligible internal resistance. The power dissipated in the coil is 25 W. What is the
resistance of the coil?
A. 0.25 Ω
B. 2.5 Ω
C. 4.0 Ω
D. 250 Ω
C.
𝑉
𝑉2
𝑃 = 𝐼𝑉 = 𝑉 =
𝑅
𝑅
100
𝑅=
= 4.0 Ω
25
20. Two identical cells, each of emf 1.6 V and internal resistance 2.0 Ω,
are connected in parallel with a 3.0 Ω resistor.
What is the current I ?
A.
A. 0.4 A
B. 0.6 A
C. 0.8 A
D. 1.6 A
1 1 1
= +
→
𝑟 2 2
𝑟 = 1Ω
𝑅 = 1 + 3 = 4Ω
𝐼=
1.6
= 0.4𝐴
4
Two voltage sources with identical emfs connected in parallel have a net emf
equivalent to one emf source, however, tha net internal resistance is less, and
therefore produces a higher current.
21. A current-carrying conductor is at right angles to a magnetic field. The
force on the conductor is F.
The conductor is turned so that it is parallel to the field with no other
changes. In what way, if any, does the force on the conductor change?
A. It is unchanged.
B. It increases so that it is greater than F.
C. It decreases so that it is greater than zero but less than F.
D. It becomes zero.
D.
Magnetic force on a wire carrying current I
in a magnetic field B: 𝐹 = 𝐵𝐼𝐿𝑠𝑖𝑛 𝜃
I = current [A]
L = length [m]
B = magnetic field [T]
𝜃 = 𝜃 is the angle between 𝐼 and 𝐵
22. An astronaut orbits the Earth in a space capsule. Which statement is correct?
A. There are no gravitational forces acting on the space capsule or the astronaut.
B. The space capsule and the astronaut each have the same acceleration.
B.
C. The space capsule and the astronaut are each in equilibrium.
D. The gravitational force on the space capsule is equal to that on the astronaut.
Gravitational force (weight) on each of them is
slightly less then it would be on Earth.
Both, capsule and astronaut are in free fall.
23. The table shows four of the energy levels for the hydrogen atom with
their corresponding energies.
Energy level
Energy / 10–19 J
6
– 0.6
4
– 1.4
2
– 5.4
1
– 21.8
When an electron changes from level 6 to level 1 the spectral line emitted
has a wavelength of 9.4 ×10–8 m. What is the approximate wavelength of the
spectral line emitted when an electron changes from level 4 to level 2?
A. 5 ×10–4 m
B. 5 ×10–7 m B.
C. 5 ×10–8 m
D. 5 ×10–10 m
𝑐 ∆𝐸
𝑐
=
→ λ=
λ
ℎ
ℎ∆𝐸
4 → 2: ∆𝐸 = 4.0 × 10−19 J
𝑓=
6 → 1: ∆𝐸 = 21.2 × 10−19 J
λ4→2 21.2 × 10−19 J
=
λ6→1
4.0 × 10−19 J
→ λ4→2 = 9.4 ×10–8
21.2
≈ 50 × 10−8
4.0
∆𝐸 around 5.3 times smaller: so wavelength should be 5.3 times greater
(smaller energy, smaller frequency, greater wavelength)
24. All isotopes of a particular element have the same
A. mode of radioactive decay.
B. half-life.
C. number of protons.
D. number of neutrons.
C.
25. The magnitude of the binding energy per nucleon is
A. a maximum for nuclides having nucleon numbers around 60.
A.
B. directly proportional to the neutron to proton ratio of nuclides.
C. a maximum for nuclides with high nuclear charges.
D. a maximum for nuclides with low nuclear charges.
With 8.8 MeV binding energy per nucleon,
iron-56 is one of the most tightly bound nuclei.
26. A positive pion is a meson consisting of an up quark and an anti-down
quark. A student suggests that the decay of the positive pion is represented
by the following equation.
The suggestion is incorrect because one of the quantities is not conserved.
Which quantity is not conserved in the student’s equation?
A. Charge
B. Baryon number
Particles without any quarks have
C. Lepton number C. a baryon number of zero.
D. Strangeness
𝜇 + 𝑖𝑠 𝑎𝑛𝑡𝑖𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒
Charge: OK
+1=+1+0
Baryon number: OK
(1/3)+( – 1/3)=0 + 0
Lepton number: OK
0= -1+(–1) NO
Strangeness:
0=0+0
S = # antistrange quarks – # strange quarks
PRACTICE: Conservation of Baryon Number
Baryons are hadrons (composite particles made of quarks) composed of any three quarks. Baryon
number is conserved in a reaction. You must count each baryon as +1 and each antibaryon as -1.
Non-baryons have a baryon number of 0.
Conservation of Lepton Number
There are six leptons: three have electric charge and three, called neutrinos, do not. The electron
is the best known lepton. The tau and the muon are the other two charged leptons. Each neutrino
is associated with one of the charged leptons.
Lepton number is also conserved in reactions. Again, leptons have lepton number of +1,
antileptons have -1, and non-leptons have 0.
This is an observed event that conserves both electric charge and baryon number.
Charge is conserved, but lepton number is not. There are no leptons on the left, but there is
one on the right. This cannot happen.
27. The blade length of a wind turbine is doubled. By what factor will the
maximum power output increase?
A. 2
B. 4 B.
C. 8
D. 16
P = ½ ρ π r2 v 3
28. The Sankey diagram shows a typical fossil-fuel plant of total efficiency 40 %.
There are frictional, electrical transmission and energy losses to the lower
temperature surroundings. Which branch represents energy losses to the
surroundings?
D. output
B. Losses to surroundings are ALWAYS
greater than internal friction (C.) or
transmission (A.)
29. The absolute temperature of a black body increases by 2 %. What is the
percentage increase in the power emitted by the black body?
A. 2
𝑃 = 𝜎𝐴𝑇 4
B. 4
C. 8
D. 16
C.
𝑃𝑛𝑒𝑤 = 𝜎𝐴 𝑇𝑛𝑒𝑤
4
Increase 2% →𝑇𝑛𝑒𝑤 = 1.02𝑇
𝑃𝑛𝑒𝑤 = 𝜎𝐴 1.02𝑇
4
≈ 1.08 𝜎𝐴𝑇 4
𝑃𝑛𝑒𝑤 ≈ 1.08 𝑃 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑜𝑓 8%
I know – no calculator -
30. What is thermal conduction mainly due to in a gas?
A. The motion of free electrons
B. Fast molecules transferring energy to slower molecules
B.
C. Slow molecules transferring energy to faster molecules
D. Lattice vibrations causing collisions with neighbouring molecules
Temperature is proportional to KE
Thermal conduction is practically only due to KE
transfer between molecules
For anything else but ideal gas, temperature is a
measure of average kinetic energy.
For ideal gas T=(3/2)kT
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
D
D
D
A
B
B
D
A
D
C
B
C
B
B
D
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
A
B
B
C
A
D
B
B
C
A
C
B
B
C
B