# Physics Unit 2

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Define speed
Just how fast you are going with no regard to direction
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Define velocity
Speed in a given direction
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Speed =
Distance / Time
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What does the gradient of a distance-time graph represent?
How fast the object is moving.
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Define acceleration
How quickly the velocity is changing. This change in velocity can be a change in speed or a change in direction or both.
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Acceleration =
Change in velocity / Time taken
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What does the gradient represent on a velocity time graph?
Acceleration (/ = acceleration or \ = deceleration)
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Weight =
Mass x Gravitational Field Strength
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When 2 object interact what happens to the forces?
Equal and Opposite
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What is a resultant forces?
The overall force on a point or object
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What might a resultant force cause an object to do?
Change it's state
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If the resultant force action on a stationary object is 0 ...
the object will remain stationary
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If the resultant force acting on a stationary object is not 0 ...
the object will accelerate in the direction of the resultant force
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If the resultant force acting on a moving object is 0...
The object will continue moving at the same speed in the same direction
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If the resultant force action on a moving object is not 0....
The object will accelerate in the direction of the resultant force
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Resultant force =
Mass x Acceleration (Resultant force in newtons (N) Mass in kilograms (kg) acceleration in meters per second squared (m/s^2))
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When a vehicle travels at a steady speed the resistant force balances...
...the driving force
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If the speed of a vehicle is increased, what will happen to the braking force>
Increase
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What is the stopping distance?
Is the sum of the distance the vehicle travels during the driver's reaction time (thinking distance) and the distance it travels under the braking force (braking distance)
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What effects the driver's reaction time?
Tiredness, drugs and alcohol
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When the braked of a vehicle are applied what increases?
Work done by the friction force betweem the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increase.
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What effects the vehicles braking distance?
Weather conditions and poor condition of the vehincle
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What happens to the acceleration when an object is falling through a fluid?
Will initially accelerate due to the force of gravity eventually the resultant force will be 0 and the object will move at its terminal velocity (steady speed_
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Weight =
m x g (W = weight in newtons, m = mass in kilograms, g = gravitational field strength in newtons per kilogram)
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Work done =
Force x Distance
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gravitational potential energy (joules) =
mass x g x height
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What is work done stored as in an elastic object?
Elastic Potential Energy
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Power is the work done or energy transferred in a given time, so.. Power =
E/t (Power in watts, Energy transferred in joules, time taken in seconds
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What is gravitational potential energy?
The energy that an object has virtue of its position in a gravitational field.
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Ep = m x g x h - What do the symbols mean?
Ep is the change in gravitational potential energy in joules, m is the mass in kilograms, g is the gravitational field strength in newtons per kilogram, h is the change in height in metres
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The kinetic energy of an object depends of its mass and its speed, What is the equation?
Ek = 1/2 x m x v^2
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Momentum is a property of moving objects. Momentum =
mass x speed
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What is the conservation of momentum?
In a closed system the total momentum before and event is equal to the total momentum after the event.
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What happens when something becomes electrically charged?
Insulating materials are rubbed against each other and they become electrically charged. Negatively charged electrons are rubbed off on material and onto the other
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What happens when 2 electrically charged objects are brought together?
They exert a force on each other
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Electrical charges can move easily through some substances, Name a kind of substance?
Metal
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What is an electric current?
A flow of electric charge. The size of the electric current is the rate of flow of electric charge
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What is the equation of the size of the current?
Current (amps) = Charge (coulombs) / Time (seconds)
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The potential difference (voltage) between two points in an electric circuit is....
The work done (energy transferred) per coulomb of charge that passes between the points
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For components connected in series:
- the total resistance is the sun of he resistance of each component - There is the same current through each component - The total potential difference of the supply is shared between the components
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For components connects in parallel:
-The potential difference across each component is the same - The total current through the whole circuit is the sum of the currents through the separate components
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As the resistance of a filament bulb increases, what happens to the temperature?
It increases
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Is the resistance high or low in the reverse direction in a diode?
Very high as the current through a diode flows in one direction only
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What is direct current?
Current that always passes in the same direction (cells and batteries)
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What is alternating current?
A current that is constantly changing direction
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What is the frequency of the mains electric in the UK?
50 hertz and 230 V
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Draw and label the structure of a 3 pin plug
.
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What breaks a circuit if the current it too great?
A fuse or a circuit breaker
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What happens to the resistor when there is a current flowing through?
It get hot
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What is power?
The rate at which energy is transferred by an appliance
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What are the masses of the particle in an atom?
Proton = 1, Neutron = 1, Electron = 0
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What are the charges of the particles in an atom?
Proton = +1, Neutron = 0, Electron = -1
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Where do some atoms give out radiation?
From their nuclei
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What is an isotope?
Atoms with the same number of protons but different number of neutrons
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What does the nucleus of alpha contain?
2 neutrons and 2 protons - the same as a helium nucleus
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What are beta particles?
Electrons
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What are the different properties of alpha, beta and gamma radiation?
Alpha particles are relatively big, heavy and sow moving. Beta particles move quite fast and they're quite small. Gamma rays have very short wavelengths and they penetrate far into materials without being stopped and pass straight through the air,
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Which radiation(s) are detected by both electric and magnetic fields?
Alpha and Beta
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What are the dangers of radiation?
Cells may become cancerous
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What type of radiation is the most penetrating?/
Alpha radiation is the least penetrating. It can be stopped - or absorbed - by just a sheet of paper. Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium. Gamma radiation is the most penetrating
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What is the half life of a radioactive iosotope
The average time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level
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What are some of the uses of radiation?
Smoke detectors (alpha), Radiotherapy (gamma rays), Sterilisation (gamma)
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What are the 2 fissionable substances in common use in nuclear reactors?
Uranium-235 and Plutonium-239
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What is nuclear fission?
Splitting of an atomic nucleus
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What is nuclear fusion?
The joining of 2 atomic nuclei to form a larger one. It's the process by which energy is released in stars
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How do stars form?
When enough gas from space is pulled together by gravitational attraction. Smaller masses may also form and be attracted by a larger mass to become planets
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During the 'main sequence' period of a stars life cycle, what are the forces?
In balance
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Why will the sun never be a black hole?
Doesn't have enough mass to collapse into a black hole. When the sun finishes its cycle it will be a red giant star
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## Other cards in this set

### Card 2

Define velocity

#### Back

Speed in a given direction

Speed =

### Card 4

#### Front

What does the gradient of a distance-time graph represent?

### Card 5

#### Front

Define acceleration