P3 OCR

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  • Created on: 26-05-11 19:36
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Physics Revision ­ P3
P3a
Speed = rate of change of distance. Speed = Distance / Time
Distance = Speed * Time
Time = Distance / Speed
Distance Time graphs = Displays data on distance and time. To calculate each gradient use the
equation speed = distance / time.
Distance time graphs can give you an overview of a journey. Comparing gradients can tell you
about the speeds.
P3b
Acceleration = Rate of increase of velocity. Calculating acceleration depends on two things, how
much the speed of the object changes and how long the change in speed takes. Equation ­--
Acceleration = Change in speed / time. OR . Metres per second squared = Metres per second squared /
seconds.
Speed-time graphs can help us understand acceleration. Looking carefully at one you can work
out specific speeds, times and acceleration.
P3c
Stopping Distances = The distance a vehicle travels from the time the driver sees a hazard to
when the vehicle comes to a rest (thinking distance + braking distance)
When you need to stop, a small amount of time is spent deciding whether or not to put your
foot on the brakes. This is the thinking distance. Can be increased by use of alcohol, tiredness and use of
drugs.
After you put your foot on the brake the car slows down but it continues to travel until it stops.
This is the braking distance. Can be increased by wet roads, icy roads, brakes not working properly,
worn down tyres.
Force = mass * acceleration (Newtons = kg * metres per second squared)
P3d
The energy transferred when a force moves an object (work = force * distance)
Two things that will make someone use up energy quicker = Having to push with a greater force,
having to push for a greater distance.
Power = Measured in Watts. It is a measure of how quickly work is being done and energy is
being transferred. It is how much work is done in one second, OR, how much energy is transferred in one
second.
P3e
Transport all need a source of energy that is transferred into kinetic energy causing movement.
Fossil fuels = Petrol, Diesel and other non-renewable sources.
Kinetic Energy = 0.5 * mass * velocity (J = 0.5 * Kg * [m/s²])

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P3f
Reducing Forces = When a car moves it has kinetic energy. When a car suddenly stops, the kinetic
energy needs to be absorbs safely and slowly enough reduce injuries. Crumple zones do this. They help
reduce injuries by changing the shape and absorbing energy through progressive, controlled and
reduced acceleration of the vehicle. A good crumple zone means that a car stops in a longer time and
longer distance. The change in speed remains the same but the deceleration will be smaller.…read more

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