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Physics 1 - Motion, Forces And Conservation Of Energy > Stopping Safely > Flashcards

Flashcards in Stopping Safely Deck (10)
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what should drivers to on the road to avoid and accident

- leave enough space in front so they could stop safely
- at least equal to the stopping distance for their speed


what happens as the speed of the car increases and why

- the thinking distance increases at the same rate
- this is because the driver's reaction time stays fairly constant
- but the higher the speed, the further you go in that time


what is the relationship between speed and braking distance

- if the speed doubles, the braking distance increases by a factor of 4 (2^2)
- and is the speed trebles, the braking distance increases by a factor of 9 (3^2)


how do brakes stop a car

- the brakes of the car do work on the car's wheels
- this transfers energy from the car's kinetic energy store to the thermal energy store of the brakes
- so to stop a car, the brakes must transfer all its energy


what is the equation which shows the energy transfer from the kinetic energy stores of the car to the thermal energy stores of the brakes

- energy in the car's kinetic stores = work done by the brakes
- (1/2 x mass x velocity^2 = force x (braking) distance)


what are the estimated masses of cars, single decker buses and a loaded lorry

- car's mass is 1000kg
- single decker bus is 10,000kg
- loaded lorry is 30,000kg


what is the estimated reaction time of a driver

1 second


what does the first part of a thinking and braking distance velocity time graph look like

- there is a solid block at the beginning
- its area gives the thinking distance
- the length of it on the time axis gives the reaction time


what does the second part of a thinking and braking distance velocity time graph look like

- a triangle, with the line at the top of the solid block going down into the time axis
- the area of the triangle gives the braking distance
- the gradient (deceleration) shows the maximum force applied by the brakes


if there were two velocity time graphs, one showing the thinking and braking distance of a man before and after being tired, would the gradient change and why

- it wouldnt
- as the deceleration is the same on both graphs
- because the maximum force applied on the brakes hasnt changed