GCSE Physics Edexcel P2 Topic 4

These are revision notes I made myself. I got A* in the Physics GCSE exam and 80 UMS (full marks) in the P2 exam using only these notes.

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P2 Topic 4: Momentum, energy, work and power
Stopping distances
Thinking distance: distance travelled between seeing hazard and applying the brake.
Braking distance: distance travelled between applying the brake the vehicle having stopped.
Stopping distance: thinking distance + brake distance
Changing stopping distances
A driver's thinking distance would be greater if their reaction time is longer ­ for example, if they are tired or
ill, or have taken drugs or alcohol.
If a vehicle is moving at a greater speed, both its thinking distance and braking distance are increased.
Friction slows vehicles down. Brakes create a lot of friction, but if they're worn, they'll create less friction and
do not slow the vehicle so well.
Friction between the tyres and road is also important. If the road is wet or has loose gravel on it, there is less
friction and the braking distance is increased.
Factor Breaking or thinking distance Examples
Mass Breaking distance A heavier vehicle means a longer
distance as more force is required to
Speed Breaking distance A faster speed means longer
braking distance
Driver's reaction time Thinking distance Being ill, tired, drugs, or alcohol
(start of reaction time affected by
distractions, fog, eyesight, driver
experience and anticipation)
Brakes Braking distance Worn brakes means further breaking
distance as they cause less friction
Road Braking distance Icy road means longer breaking
distances (as well as oil and water)
Tyre friction Braking distance Icy or wet road means less friction

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If two vehicles are going at the same speed hit a barrier, the barrier moves more when hit by a monster truck
rather than a small car as it has more momentum.
Momentum: a measure of how strongly something is moving. It is calculated by multiplying mass by velocity.…read more

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(joules, J) = (newtons, N) x (metres, m)
Power is the rate of doing work. It is measured in watts (W). 1 watt means 1 joule of work done per second.
work done (joule, j)
power (watt, W) =time taken (second,s)
P= t
Potential and kinetic energy
Gravitational potential energy is energy that is stored because of an object's position in a gravitational field.
Essentially, on Earth if something can fall it has gravitational potential energy.…read more


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