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63 Cards in this Set
- Front
- Back
What is the equation for distance?
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Distance = speed / time
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What is the equaion for average speed?
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Average speed = (u + v) / 2
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Distance time graphs
a) What does the gradient represent? b) What do flat sections represent? c) A steeper gradient means what? d) Curves represent what? e) A "downhil" section means what? |
a) Speed
b) The vehicle has stopped c) A faster speed d) Acceleration/deceleration e) It's changed direction and is coming back to its starting point |
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How do you calculate speed from a distance time graph?
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Using the gradient (y/x)
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What is acceleration?
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How quickly the speed is changing
You can also accelerate when changing direction, with or without changing speed |
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What is the equation for acceleration?
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Acceleration = change in speed / time taken
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Speed time graphs
a) What does the gradient represent? b) What do flat parts of the graph represent? c) What does a steeper gradient mean? d) What do uphill and downhill sections mean? e) What does a curve mean? |
a) Acceleration
b) Steady speed c) Greater acceleration/deceleration d) Uphill = acceleration Downhill = deceleration e) Non-uniform (changing) acceleration/deceleration |
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How do you work out the distance travelled from a speed time graph?
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The area under the graph
Eg Triangle = (bxh) / 2 |
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What is the difference between mass and weight?
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Mass = a measure of how much matter is in an object
Weight = caused by the pull of gravity and is a force |
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What is the equation for weight?
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weight = mass x gravitational field strength
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What are the 6 different types of forces?
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1. Gravity or weight = always downwards
2. Reaction force from a surface = usually upwards 3. Thrust/push/pull due to an engine/rocket speeding something up 4. Drag/air resistance/friction = slowing something down 5. Lift due to a plane wing 6. Tension in a rope/cable |
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How must the forces be in order for an object to be stationary?
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Balanced
Force of gravity acts down Causes a reaction force from the surface, pushing up |
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How must the forces be in order for a steady horizontal speed?
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Balanced
Force of gravity/weight acts down Reaction force from surface, pushing up Thrust Drag/air resistance |
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How must the forces be in order for horizontal acceleration?
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Unbalanced
A larger thrust than air resistance/drag (Gravity and reaction force are still balanced) |
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How must forces be in order for a steady vertical speed?
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Balanced
Weight acts downwards Air resistance/drag upwards Eg. skydiver |
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How much forces be in order for vertical acceleration
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Unabalanced
Force of weight bigger than drag/air resistance |
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What is the equation for force?
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Force = mass x acceleration
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What is the equation for stopping distance?
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Stopping distance = thinking distance + braking distance
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What is thinking distance defined as?
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The distance the car travels in the time between the driver noticing the need to brake and applying the brakes
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What factors affect thinking distance
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Speed: Faster speed = further distance
Tiredness Drugs and alcohol Distractions A Lack of concentration |
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What is braking distance define as?
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The distance taken to stop once the brakes have been apllied
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What factors affect braking distance?
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1) Speed: Faster speed = further distance
2) Mass: Heavier vehicale = longer takes to stop 3) Brake quality = if worn or fault won't be able to brake with as much force 4) Grip = icy/wet conditions and tyre treads |
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What is the relationship between speed and thinking distance? Why is this?
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- Linear =Thinking distance increases at the same rate as speed
- Thinking time stays constant but the more distance you cover in that time if speed is greater |
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What is the relationship between speed and braking distance?
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A squared relationship = As speed doubles, braking distance quadruples
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Why is speed and braking distance a squared relationship?
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Kinetic energy Transferred = Work done by brakes
1/2 x M x V(2) = F x d (d = braking distance, f = braking force) 'F' is always the maximum possible braking force, d must increase to make the equation balance/to convert the extra KE |
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What is the equation for momentum? (kgm/s)
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Momentum (kgm/s) = Mass (kg) x Velocity (m/s)
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How can you use Newton's 2nd law of motion to explain that when a force acts, it causes a change in momentum?
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Force = mass x acceleration
1) Any force applied increases it acceleration 2) Acceleration is change in velocity over time 3) A change in momentum can be caused by a change in velocity so any force applied to an object over time causes a change in momentum |
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When is work done?
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Whenever a force moves an object in a certain distance
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What is the equation for work done?
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Work (J) = force (N) x ditance moved in direction of force (m)
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Explain how seatbelts protect the occupant
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- The seatbelt will stretch a little once locked and allow to stop more slowly. In stretching, the seatbelts absorb kinetic energy and convert it to elastic energy, reducing injuries.
- Reduces rate of change of momentum F= change in momentum/time |
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Explain how crumple zones protect the occupant
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- They change shape on impact at the front and back of the car. By changing shape they absorb energy and increase the time between impact and stopping
- Reduces rate of change of momentum F= change in momentum/time |
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Explain how airbags protect the occupant
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- They inflate on impact and slow passengers down more slowly. It prevents them hitting the dash-board/steering wheel. They absorb some kinetic energy, reducing the injuries
- Slow passenger down |
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Explain how crash barriers protect the occupant
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They are made from a material that changes shape on impact so the car travels further before stopping
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Explain how roll cages protect the occupant
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Rigid frame inside the car. Prevents the car from collapsing and crushing the occupants in a roll crash
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Explain how traction control prevents accidents
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Stops wheels from spinning when accelerating quickly. Gives maximum grip and stability during acceleration
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Explain how brakes prevent accidents
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The brakes get hot and transfer some of the cars kinetic energy, slowing down the car
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Explain how an escape lane prevents accidents
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They are often on steep hills and allow vehicles that have failed brakes to stop by slowly by running into an upward slope with a rough surface
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Explain how ABS prevents accidents
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- Gives vehicle stability and allows driver to maintain steering during hard braking in slippery conditions
- Driver must press the pedal fully - Wheel speed sensors send information to computer about rotational speed - Computer uses information to control pressure to the brakes and applies the amount to prevent the wheels from locking up - Brakes pump on and off - Driver gets maximum braking force without skiiding and can still steer the car. The car can stop in a shorter distance but not necessarily quicker |
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What causes injuries in a vehicle collision?
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When there is a sudden change in momentum and a large force is exerted which causes rapid acceleration of body parts
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How are safety features tested?
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- Crashing cars containting dummies both with and without the safety features and watching slow motion film to see the results
- The dummies have sensors at different places to show where a real person would be injured and it's severity - Repeat tests and different cars, speeds and sized dummies - Results are compared to real data on deaths/severe injuries to see if there is a benefit |
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What is gravitational potentional energy?
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The energy that something has because of its heigh above ground. The energy uses to raise it is "stored" and can be changed to KE if it falls
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What is the equation for gravitational potential energy?
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GPE = mass x gravitational field strength x height
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What is kinetic energy?
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The energy something has when moving
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What does the kinetic energy of something depend on? Why?
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Speed
Mass Greater mass/speed = more KE |
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What is the equation for kinetic energy?
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KE = 1/2 x mass x speed (squared)
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What happens when something falls?
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Its gravitational potential energy is converted into kinetic energy
The further it falls, the faster it goes KE gained = GPE lost |
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What happens to a falling objects speed/KE reaches terminal speed?
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Speed cannot increase, so KE doesn't increase
The GPE is transferred to internal energy of the object or is used in heating up the air particles through friction |
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How do you work out the height that something needs to fall from to reach a certain speed?
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h= v (squared) + 2 x gravitational field strength
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Explain energy transfer in a rollercoaster
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At top = lots of GPE
Descends = GPE transferred to KE = speeds up At bottom of drop = minimum GPE, maximum KE |
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What is power?
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How quickly work is done
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What is the equation for power?
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Power (W) = Work done (J)
Time (s) |
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Prove that Power = Force x Speed
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Work done = Force x distance
Speed = Distance / Time Workdone = Force x speed x time /time Cancel out time Combining = Force x Speed |
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Why do larger, more powerful engines usually have a high fuel consumption?
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They transfer more energy from its fuel every second
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What is fuel consumption often given in?
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Miles per gallon (mpg)
Litres per 100km (l/100km) |
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What 6 things effect fuel consumption?
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Engine size
Mass of car Driving style (faster accelerations/harder braking) Speed Road conditions Shape of car (Roof box = increases air resistance) |
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What 3 emissions are released when cars burn fuel?
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Carbon dioxide, Nitrogen dioxide and water vapour
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What environmental problems can car emissions cause?
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Acid rain and global warming
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What are two alternative fuel sources for cars?
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Electricity
Biofuels |
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What advantages does running cars on biofuel have?
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Made from plants/organic waste = renewable = won't run out
Doesn't produce much pollution at the point of use No overall increase in carbon dioxide (plants take in CO2 and produce it when burnt) |
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What advantage does running cars on electric have?
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Doesn't release energy at the point of us
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What disadvantages do electric cars have?
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- Electricity comes from power stations that burn fossil fuels
- Expensive to make and buy - Limited performance compared to fossil fuels |
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What is one way around using power stations to produce electricity as a fuel for cars?
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Using solar panels to change energy from the sun into electricity to power the motor
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P3
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P3
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