Stopping Safely Flashcards Preview

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

Flashcards in Stopping Safely Deck (10)
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1

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

2

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

3

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)

4

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

5

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)

6

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

7

what is the estimated reaction time of a driver

1 second

8

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

9

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

10

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