Physics Flashcards
(128 cards)
0
Q
What does the gradient of a distance-time graph represent?
A
The speed of the object.
The steeper the gradient, the greater the speed.
1
Q
What is a distance time graph?
A
A graph to help us describe the motion of an object.
2
Q
How do we work out speed?
A
Speed = distance / time
m/s = m / s
3
Q
What is the speed of an object?
A
The distance travelled each second.
4
Q
What does a horizontal line on a distance-time graph mean?
A
The object is stationary.
5
Q
What does a straight vertical line on a distance time graph mean?
A
The object is moving at a constant speed.
6
Q
What is the speed of a runner who covers 400m in 50 s?
A
8 m/s
7
Q
What is velocity?
A
The velocity of an object is it’s speed in a given direction.
If an object changes direction it changes velocity, even if it’s speed stays the same.
8
Q
What do we call the change in velocity?
A
Acceleration
9
Q
What is the unit for acceleration?
A
m/s 2
10
Q
What is the equation to work out acceleration?
A
Acceleration = (final velocity - initial velocity) / time A = V - U / T
m/s 2 = m/s - m/s / s
(V - U also means change in speed)
11
Q
What happens if the value for acceleration is negative?
A
It’s decelerating or negatively accelerating.
12
Q
What does a horizontal line on a speed-time graph mean?
A
A steady, constant speed.
13
Q
What does a stationary object look like on a distance-time and speed-time graph?
A
D.T. - a horizontal line
S.T. - no line at all
14
Q
What does a constant acceleration look like on a distance-time and speed-time graph?
A
D.T. - an upwards curve (which goes right then up)
S.T. - a positive, straight line
15
Q
What does steady deceleration look like on a distance-time and speed-time graph?
A
D.T. - a downwards curve (which goes up then right and stays horizontal)
S.T. - a negative, straight line
16
Q
What does an object going backwards at a constant speed look like on a distance-time and speed-time graph?
A
D.T. - a straight, negative line
S.T. - a horizontal line
17
Q
What does an object constantly accelerating backwards look like on a velocity and speed-time graph?
A
S.T. - a positive, straight line
V - a negative, straight line
18
Q
What is acceleration?
A
Change of velocity per second
19
Q
What does the area under the line (between the line and the x axis) represent in a velocity time graph?
A
Distance travelled.
20
Q
What does the gradient of a velocity time graph mean?
A
Acceleration.
The steeper the line, the greater the acceleration. If the line is horizontal, there is no acceleration so it’s travelling at a constant speed.
21
Q
What does calculating the gradient of a D.T and S.T graph tell us?
A
D.T. - speed
S.T. - acceleration
22
Q
What is average speed of a car that travels 1.2 km in 1 minute?
A
1.2 km = 1200 m
1 minute = 60 seconds
1200m / 60s = 20
20 m/s
23
Q
What are action and reaction forces?
A
Objects always exert equal and opposite forces on each other.
If object A exerts a force on object B, object B exerts an equal and opposite force on object A.
These are called action and reaction forces.
24
What is the resultant force?
The single force that would have the same effect on the object as all the original forces acting together.
The combined effect of all forces acting upon an object.
A resultant force always causes an acceleration so if there's no acceleration, the resultant force must be 0.
The bigger the resultant force, the greater it's acceleration.
The greater the mass of an object, the smaller it's acceleration for a given force.
A resultant force always causes acceleration.The greater the resultant force on an object is the greater its acceleration. The big of a mass of an object the bigger the force needed to give it a particular acceleration
25
If there are 3 cars
1) driving force 200N - resistance force 200N
2) driving force 300N - resistance force 200N and
3) driving force 100N - resistance force 200N
which car would start moving?
Car 2 as the driving force is greater than the resistance force.
26
What is the resultant force of a 4N force and a 3N force acting in the same direction?
7N
27
What is the equation for force?
Force = mass x acceleration
F = m x a
N = kg x m/s 2
28
Which object has the greatest force acting upon it?
| A 5kg rock accelerating at 3 m/s 2 or a 7kg boulder accelerating at 2 m/s 2?
N = kg x m/s 2
1) N = 5 x 3
N = 15
2) N = 7 x 2
N = 14
A 5 kg rock a" at 3 m/s 2 has the biggest force.
29
What is the stopping distance?
The stopping distance if a vehicle is the distance it travels during the driver's reaction time (the thinking distance) plus the distance it travels under the braking force (the braking distance).
Stopping distance = thinking distance + braking distance
30
What is the thinking distance?
How long it takes to process the response.
| The thinking distance is increased if the driver is tired or under the influence if alcohol or drugs.
31
What is the braking distance?
The distance travelled while braking. This is increased by poorly maintained roads, speed of the car, bad weather or poor car conditions e.g. Worn out tyres or brakes.
32
If an object falls freely, what is the resultant force acting upon it?
Gravity. We call the force of gravity weight.
The equation F = m x a becomes:
Weight = mass x acceleration due to gravity
W = m x g
N = kg x m/s 2
33
What is Hooke's law?
The law that states that the extension of springs and elastic objects is directly proportional to the force applied, provided the limit of proportionality is not exceeded.
34
What is Hooke's law's equation?
```
Force = spring constant x extension
N = N/m x m
```
(Spring constant measures how stiff the spring is. The larger the spring constant, the stiffer the spring.)
35
A spring has a spring constant of 30 N/m. If the extension is 0.30 m, what is the applied force?
```
F = k x e
F = 30 x 0.30
F = 9N
```
36
What's work?
Energy transferred by a force
What done to overcome friction is transferred as energy that heat the object that rubs together and the surrounding
37
What's the equation for work done?
W = F * d
Work done = force * distance moved
J = N * m
38
What is the work done on an object if a force of 300N moves it at a distance of 8m?
```
W = F * d
J = 300 * 8
```
= 2400J
39
What's GPE?
Gravitational potential energy is energy stored in an object because of its position in the Earth's gravitational field.
Whenever an object is moved vertically upwards, it gains gravitational potential energy equal to the work done on it by the lifting force.
(It depends on the objects weight and how far it moves vertically)
40
What's the equation for GPE?
E = m * g * h
Energy = mass * gravitational field strength * height
J = kg * N/Kg * m
41
What's the increase in GPE when a mass of 40kg is lifted 8m?
| If it takes 2 seconds, what's the power developed?
GPE = 40 * 8
= 320J
P = 320 / 2
= 160 watts
42
What's kinetic energy?
Movement of an object measured where the greater the mass and faster the speed of the object, the more kinetic energy it has.
43
What's the equation for kinetic energy?
E k = 1/2 * m * v2
= 1/2 * mass * speed 2
= 1/2 * kg * m/s 2
44
What's the equation for momentum?
P = m * v
Momentum = mass * velocity
Kg m/s = kg * m/s
Objects have momentum when they're moving
Whenever objects interact the total momentum before the interaction is equal to the total momentum afterwards - this is the law of the conservation of momentum
Like velocity, momentum has size and direction - while one direction is positive, the other must be negative.
Objects at rest have a momentum of 0. In an explosion, they move apart with equal and opposite forces.
45
What is the momentum of a 1000 kg car travelling at 30 m/s?
P = m * v
P = 1000 * 30
= 30,000kg m/s
46
What is impact time?
Time taken for a collision to take place
The the impact time is short, the forces on the object are large - as impact time increases, the force becomes less.
47
How have cars been made safe?
Seat belts and air bags spread the force across the chest and they also increase the impact time.
Side impact bars and crumple zones give way in an impact so increasing the impact time.
48
What happens to a passenger in a collision if they're not wearing a seatbelt or have a very narrow seat belt?
Without one, they will continue forwards and hit the windscreen.
If it's narrow, the force isn't spread and may cut them.
49
What is the equation for power?
Power = energy / time
OR
Power = current * voltage
P = I / V
50
How does an insulator become negatively charged?
It gains electrons
Objects with opposite electric charges attract
Objects with the same electric charges repel
51
What's the equation for the current of the circuit?
```
Current = charge / time
I = Q / t
```
Amps = c / s
52
What is ohms law?
Ohms law states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor.
Reversing the current through component reverses the potential difference across it
53
What's the equation for resistance?
```
R = v / I
Resistance = volts / current
```
54
What is the equation for voltage?
Potential difference, work done and charge related by the equation:
V = W / Q
As work done is equal to energy transferred we can also say that:
V = E / Q
Or V = I * R
55
What is potential difference?
A measure of the work done or energy transferred to the lamp by each coulomb of charge that passes through.
The unit of potential difference is the volt.
56
What's a parallel circuit?
Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel. The total amount of current flowing into the junction, or split, is equal to the total current flowing out. The current is described as being conserved.
When components are connected in the circuit so that the potential difference is the same across each one.
57
What's a series circuit?
Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows through each component connected in series is the same.
Components connected in the circuit so that the same current passes through them are in series with each other.
58
What happens in a the filament bulb?
Resistance increases with increase of the filament temperature.
It reaches a point where no more electrons can be passed
The light on the current potential difference graph for a filament bulb is a curve so the current is not directly proportional to the potential difference
The resistance increases as the current increases because the resistance increases as the temperature.
The graph goes horizontal, curves upwards then goes horizontal again
59
What is a fixed resistor?
The symbol is just a box
It limits the current
The voltage is directly proportional to the current
60
What does a diode do?
The symbol is a circle with a triangle and line in it.
It only allows current to move in one direction.
A light emitting diode emits light e.g. an LED. voltage and current increase directly proportionally but the current only works one way.
It's graph looks horizontal up to 1 then curves upwards.
61
What does a thermistor do?
As temperature increases resistance decreases.
62
What does an LDR do?
A light dependent resistor decreases the resistance when light intensity increases
63
How can you find the total resistance in a series circuit?
Add all the individual resistances.
64
Features of a series circuit
The current is the same in each component
Adding the potential differences gives the total potential difference
Adding the resistances gives the total resistance
65
Features of a parallel circuit
The total current is the sum of the currents through the separate components
The bigger the resistance of the components the smaller the current is
The potential difference is the same across each component
66
What's the equation for energy transferred?
```
E = V * Q
Energy = volts * charge
```
67
What are the three types of radiation?
Alpha
Beta
Gamma
68
What's a radioactive substance?
A substance which contains unstable nuclei that become stable by emitting radiation.
Radioactive decay is a random event - we cannot predict or influence when it happens.
69
What's background radiation?
Radiation from radioactive substances in the environment, space or devices like X-rays.
70
What happens during alpha (radiation) decay?
The nucleus loses 2 protons and 2 neutrons.
2 protons and 2 neutrons are emitted as an alpha particle
4
a
2
They have +2 charge
71
What happens during beta (radiation) decay?
A neutron in the nucleus changes into a proton, which stays in the nucleus, and a high energy electron, which instantly emitted.
0
b
-1
They have -1 charge
72
What happens during gamma radiation?
When a nucleus emits gamma radiation, there is no change in the atomic number or the mass number.
A gamma ray is an electromagnetic wave released from the nucleus. It has no change in change and no mass.
73
What's ionisation?
| Radiation
When nuclear radiation travels through a material it will collide with the atoms of the material, knocking the electrons off and creating ions.
Ionisation in a living cell can damage or kill the cell.
74
Properties of alpha particles:
Alpha particles are relatively large, so they have lots of collisions with atoms - because they are strongly ionising.
Because of the collisions, the alpha particles don't penetrate far into the material.
They can be stopped by a thin sheet of paper, human skin or a few cm of hair.
They have a positive charge and are deflected by electric and magnetic fields.
75
Properties of beta particles:
Much smaller and faster than alpha particles so are less ionising and penetrate further.
They are blocked by a few metres of air or a thin sheet of aluminium.
Beta particles have a negative charge and are deflected by electric and magnetic fields in the opposite direction to alpha particles.
76
Properties of gamma rays:
They're electromagnetic waves so they will travel a long way through a material before colliding with an atom.
They are weakly ionising and very penetrating.
Several cm of lead or several metres of concrete are needed to absorb most of the radiation.
Gamma rays are not defected by electric or magnetic fields.
77
What's half life?
| Radioactivity
The time that it takes for half of the atoms in a sample to decay.
The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
We use the half life to measure how quickly the radioactivity decreases. It is the time taken for the count rate from the original isotope to fall to half it's initial value.
The half life is the same for any sample of the particular isotope.
78
What are alpha sources used for?
Smoke alarms
The alpha particles are not dangerous because they are poorly penetrating. The source needs a half life of several years.
79
What are beta sources used for?
Thickness monitoring in the manufacture of things like paper or metal foil.
Alpha particles would be stopped by a thin sheet of paper all gamma rays would pass through it. The source needs a half life of many years so that decreases in count rate are due are due to changes in the thickness of the paper.
80
What are gamma and beta sources used for?
Used as tracers (give information) in medicines.
The source injected or swallowed by the patient. It's progress around the body is monitored by a detector outside the patient. The source needs. Half life of a few hours so that the patient is not exposed to unnecessary radioactivity.
81
What's radioactive dating?
Radioactive dating is used to find the age of ancient material.
Carbon dating is used to find the age of wood and other organic material.
Uranium dating is used to find the age of igneous rocks.
82
Why isn't an alpha source used as a tracer in medicine?
Alpha particles are very poorly penetrating so they wouldn't be detected outside of the body.
Alpha is very ionising so would be damaging to the patient.
83
What's radiation?
The particles or waves emitted by radioactive substances. Nuclear radiation comes from the nucleus of a radioactive atom.
In a radioactive atom, the nucleus is unstable and so it emits particles or waves to form a more stable atom. This process is called radioactivity or radioactive decay which is a natural, spontaneous process.
84
What type of particle is an alpha, beta and gamma atom?
Alpha: He nucleus (4, 2 - 2 protons 2 neutrons)
Beta: electron
Gamma: none - it's a wave
85
What are the ionising effects of alpha, beta and gamma radiation and are they affected by electric/magnetic fields?
Alpha: strongly causes ionisation.
It is affected by magnetic/electric fields.
Beta: weakly causes ionisation.
Is bent/ deflected strongly by magnetic/electric fields.
Gamma: very weakly causes ionisation.
Not affected by magnetic/electric fields.
Alpha - stopped by paper or a few centimetres of air
Beta - stopped by thin metal or a metre of air
Gamma - stopped by thick lead and has an unlimited range in air
They can be separated by a magnetic or electric field and they ionise substances they pass through
86
What are the dangers of the different types of radiation?
The degree to which each different type of radiation is most dangerous to the body depends on whether the source is outside or inside the body.
If the radioactive source is inside the body, perhaps after being swallowed or breathed in:
Alpha radiation is the most dangerous because it is easily absorbed by cells
Beta and gamma radiation are not as dangerous because they are less likely to be absorbed by a cell and will usually just pass right through it
If the radioactive source is outside the body:
Alpha radiation is not as dangerous because it is unlikely to reach living cells inside the body
Beta and gamma radiation are the most dangerous sources because they can penetrate the skin and damage the cells inside
87
What is radioactive decay?
A spontaneous, random process that cannot be controlled and is not affected by temperature (or pressure?)
Each radioactive element has it's own particular decay rate (half-life)
88
What does the gradient of the line on a velocity-time graph show?
Acceleration
89
What does the gradient of the line on a distance-time graph show?
Speed
90
What's charging by friction?
When two electrically insulating materials are rubbed together, electrons are rubbed off one material and deposited on the other (which way round depends on the particulate materials).
Electrons have a negative charge so the material that has gained the electrons becomes negatively charged and the one which has lost electrons becomes positively charged. This is called changing by friction.
Objects with opposite electrical charges attract and objects with the same repel.
The bigger the distance between the objects, the weaker the force between them.
91
What's the equation for current in a circuit?
Current = voltage / resistance
I = V/R
92
What is direct and alternating current?
Direct current (dc) is current in one direction only (and looks like a straight line on an oscilloscope) and is supplied from cells and batteries that pass through a one-way circuit.
Alternating current (ac) is current which repeatedly reverses in direction (and looks live a wave -going positive and negative - on an oscilloscope) and is supplied from the mains supply.
93
What's the peak voltage of an alternating current?
The peak voltage of an alternating potential difference is the maximum voltage measured from zero volts.
The frequency of the UK mains supply is 50 Hz which means it changes direction 50 times each second. The voltage of the mains is 230 V.
The live wire of the main supply alternates between a positive and negative potential with respect to the neutral wire. The neutral wire stays zero volts.
The live wire alternates between peak voltages of 325 V and -325 V. In terms of electrical power, this is equivalent to a direct potential difference of 230 V.
94
What is the potential of the neutral terminal?
0 V
95
What is the outer cover of a three pin plug made of?
Rubber or plastic.
Both of these materials are good electrical insulators.
These stiff plastic materials enclose the electrical connections.
96
What are the 3 pins of the plug made of?
Brass - it's a good electrical conductor, it's hard and won't rust or oxidise.
97
What are the different wires of a plug?
Cables consist of two or three insulative copper wires surrounded by an outer layer of flexible plastic material.
In a three pin plug or three core cable:
- the live wire is red or brown
- the neutral wire is blue
- the earth wire is green and yellow
98
Why must appliances with metal cases be earthed?
Appliances with metal cases must be earthed - the case is attached to the earth wire in the cable to prevent electric shocks.
If appliances with metal cases develop faults and the live wire touches the metal case, the case becomes live and could give a shock to anyone who touches it.
This is a fuse is always fitted with a live wire.
Appliance with plastic cases don't need to be earthed and are said to be double insulated and are connected to the supply with two-core cable containing just a live and neutral wire.
They don't need to be earthed because plastic is an insulator and cannot become alive.
Cables of different thicknesses are used for different purposes. The more current to be carried, the thicker the cable needs to be.
99
What is a fuse?
A fuse contains a thin wire that heats up and melts if too much current passes through it. This cuts off the current.
If a fault develops in an earthed appliance, a large current flows to earth and melts the fuse, disconnecting the supply.
The rating of the fuse should be slightly higher than the normal working current of the appliance.
If it is much higher, it will not melt soon enough.
If it is not higher than the normal current, it will melt as soon as the appliance is switched on.
100
What's the circuit breaker?
A circuit breaker can be used in place of the fuse. This is an electromagnetic switch that opens and cuts off the supply if the current is bigger than a certain value.
101
What's the residual current circuit breaker (RCCB)?
A residual current circuit breaker cuts of the current in the live wire if it is different to the current in the neutral wire it works faster than a fuse or an ordinary circuit breaker.
102
What is an electric current and what is the equation to work out charge?
The rate of flow of charge
```
Charge = current * time
Q = I * t
```
103
How can the amount of energy transferred be calculated?
By the equation:
```
Energy = voltage * charge
E = V * Q
```
104
What are electrical faults and how can they be prevented?
Electrical faults may occur as a result of damage to sockets, plugs cables or appliances.
They are dangerous because they can cause electric shocks and fires.
Never touch a mains appliance or plug in socket with wet hands.
Never touch a bare wire or a terminal at a potential of more than 30 V.
Check cables plugs and sockets for damage regularly.
Avoid overloading sockets as this may cause overheating and a risk of fire.
105
What's the activity of a radioactive source?
The number of nuclei that decay per second.
106
What is nuclear fission?
Nuclear fission is the splitting of the nucleus into two approximately equal fragments and the release of two or three neutrons.
Nuclear fission happens when a neutron hits uranium 235 nucleus or plutonium 239 nucleus in the nucleus splits.
The chain reaction occurs when neutrons from the fish and go onto cause other fission events.
A slow moving neutron is fired at the radioactive nuclei.
The nucleus then absorbs the neutron and becomes unstable.
This causes the nucleus to split into two smaller daughter nuclei.
In this process 2 or 3 neutrons are emitted and lots of energy is also released.
These neutrons then go on to be absorbed by other radioactive nuclei which also split and so on forming a chain reaction.
The energy released in such a nuclear process is much greater than the energy released in a chemical process such as burning.
107
What is nuclear fusion?
Nuclear fusion is the process of forcing two nuclei close enough together to form a single, large nucleus.
Nuclear fusion can be brought about by making two light nuclei collide at very high speed.
Fusion is the process by which energy is released in stars.
There are many difficulties with producing energy from nuclear fusion reactors.
Nuclei approaching each other will repel one another due to their positive charge.
To overcome this, the nuclei must be heated to a very high temperature to give them enough energy to overcome the repulsion and fuse.
Because of the enormously high temperatures involved, the reaction cannot take place in a normal container but has to be contained in a magnetic field.
108
What are the major sources of background radiation?
Radon gas which seeks through the ground from radioactive substances and rocks. This emits alpha particles so is a hazard if inhaled.
Other sources include cosmic rays from outer space, food and drink, air travel and nuclear weapons testing.
Medical sources include X-rays.
109
What are the nuclear issues?
Radioactive waste
Accidents can lead to catastrophes
But
It doesn't produce any greenhouse gases
It produces more energy than fossil fuel sources
110
What was the early universe like?
The universe was a hot, glowing ball of radiation. As the universe expanded, the temperature fell.
Before galaxies and stars, the universe was formed of hydrogen and helium. Eventually dust and gas were pulled together by gravitational attraction to form stars.
The resulting intense heat started off nuclear fusion reactions in the stars so they began to emit visible light and other types of radiation.
A galaxy is a collection of billions of stars held together by their own gravity.
111
What's a protostar?
A gas and dust cloud in space that can go on to form a star.
It becomes denser and the nuclei of hydrogen atoms and other light elements start to fuse together, releasing energy.
Stars radiate energy because of hydrogen fusion in their core. This stage can continue for billions of years until the star runs out of hydrogen nuclei.
The star is stable because the inward force of gravity is balanced by the outward force of radiation from the core and is called the main sequence star.
When the star runs out of hydrogen it swells, cools down and turns red.
112
What happens in the star life-cycle of a low mass star?
```
Protostar (clouds of dust and gas)
Main sequence star (stable)
Red giant (low mass)
White dwarf (fusion stops and the star contracts)
Black dwarf (no more light is emitted)
```
113
What happens in the star life-cycle of a high mass star?
```
Protostar (clouds of dust and gas)
Main sequence star (stable)
Red supergiant (much larger than our sun/mass)
Supernova (star explodes)
Black hole if there's sufficient mass
```
A supernova is the explosion of a supergiant after it collapses.
114
How are chemical elements formed?
They're formed by fusion in stars. Nuclei of lighter elements fuse to form the nuclei of heavy elements; this process releases lots of energy.
Elements heavier than iron are formed in supernovas, along with lighter elements.
The sun and the rest of the solar system were formed from the debris of a supernova.
115
What is the difference between mass and weight?
Mass is the amount of matter in an object
| Weight is the force of gravity acting upon it
116
What is drag force?
A force opposing the motion of an object due to fluid e.g air flowing past the object as it moves.
The faster the object falls the bigger the drag force becomes until eventually it will be equal to the weight of the object.
The resultant force is now 0 to the body stops accelerating.
It moves at a constant velocity called the terminal velocity
117
What is the total momentum after an explosion equal to?
Total momentum before the explosion
118
What does the graph for a filament bulb look like?
(Negative) horizontal then curves upwards and is (positive) horizontal
119
What's the graph for a diode?
Horizontal at 0 until almost 1V on the x axis then it increases
120
What's an alternating current?
One which repeatedly changes direction (positive and negative)
121
How is power calculated?
P = E / t
Power (W) = energy transferred (joules) / time (s)
P = I * V
122
It is safer for a car driver to be wearing a seat belt, compared with not wearing a seat belt, if the car is involved in a collision.
Explain why:
the seat belt stretches
driver takes a longer (impact) time to slow down and stop (than a driver hitting a hard surface/windscreen/ steering wheel)
for the (same) change of momentum
a smaller force is exerted (so driver less likely to have serious injury than driver without seat belt)
or
the seat belt stretches (1)
driver travels a greater distance while slowing down and stopping (than a driver hitting a hard surface/windscreen/ steering wheel) (1)
for (same) amount of work done (1)
a smaller force is exerted (so driver less likely to have serious injury than driver without seat belt) (1)
123
There is an increase in both the resistance and the temperature of the metal filament inside the bulb.
Explain, in terms of the electrons and ions inside the filament, why both the temperature and the resistance increase.
ions vibrate faster
or
ions vibrate with a bigger amplitude
electrons collide more (frequently) with the ions or
(drift) velocity of electrons decreases
electrons collide more (frequently) with the ions or
(drift) velocity of electrons decreases
or
(drift) velocity of electrons decreases
124
It is safer for a car driver to be wearing a seat belt, compared with not wearing a seat belt, if the car is involved in a collision.
Explain why:
the seat belt stretches
driver takes a longer (impact) time to slow down and stop (than a driver hitting a hard surface/windscreen/ steering wheel)
for the (same) change of momentum
a smaller force is exerted (so driver less likely to have serious injury than driver without seat belt)
or
the seat belt stretches (1)
driver travels a greater distance while slowing down and stopping (than a driver hitting a hard surface/windscreen/ steering wheel) (1)
for (same) amount of work done (1)
a smaller force is exerted (so driver less likely to have serious injury than driver without seat belt) (1)
125
There is an increase in both the resistance and the temperature of the metal filament inside the bulb.
Explain, in terms of the electrons and ions inside the filament, why both the temperature and the resistance increase.
ions vibrate faster
or
ions vibrate with a bigger amplitude
electrons collide more (frequently) with the ions or
(drift) velocity of electrons decreases
electrons collide more (frequently) with the ions or
(drift) velocity of electrons decreases
or
(drift) velocity of electrons decreases
126
What happens when an object falls through a fluid?
The fluid exerts a drag force / air resistance on the object, resisting it's motion.
The faster the object falls, the bigger the drag force becomes, until eventually it will be equal to the weight of the object.
The resultant force is now zero so the body stops accelerating.
It moves at a constant velocity called terminal velocity.
127
What type of transformer is used in phone chargers?
A switch mode transformer
