Topic 5 - Forces (4)

Question 1

STOPPING DISTANCES:
What happens when a driver performs an emergency stop?

Answer 1

maximum force is applied to the breaks i order to stop the car i the shortest distance possible
(the longer is takes to perform the emergency stop, the higher the risk of crashing into whatever’s in front)

Question 2

STOPPING DISTANCES:
What is meant by stopping distance?

Answer 2

the distance it takes to stop a car in an emrgency

Question 3

STOPPING DISTANCES:
How do you find the stopping distance of a car?

Answer 3

stopping distance = thinking distance + breaking distance

Question 4

STOPPING DISTANCES:
What is thinking distance?

Answer 4

how far the car travels during the driver’s reaction time

Question 5

STOPPING DISTANCES:
What is driver’s reaction time?

Answer 5

the time between the driver seeing a hazard and applying the breaks

Question 6

STOPPING DISTANCES:
What is braking distance?

Answer 6

the distance taken to stop under the breaking force (once the breaks are applied)

Question 7

STOPPING DISTANCES:
What are the typical car braking distances for each speed?
- 30 mph
- 60 mph
- 70 mph

Answer 7

• 14m
• 55m
• 75m

Question 8

STOPPING DISTANCES:
What are the two main factors that affect thinking distance?

Answer 8

• your speed
• reaction time

Question 9

STOPPING DISTANCES:
How does speed affect thinking distance?

Answer 9

the faster you’re going, the further you’ll travel during the time it takes you to react

Question 10

STOPPING DISTANCES:
Hpw does reaction time affect your thinking distance?

Answer 10

the longer your reaction time, the longer your thinking distance

Question 11

STOPPING DISTANCES:
What are the 4 main factors that can affects braking distance?

Answer 11

• speed
• weather or road surface
• condition of your tyres
• how good your breaks are

Question 12

STOPPING DISTANCES:
How does speed affect braking distance?

Answer 12

for a given braking force, the faster a vehicle travels, the longer it takes to stop

Question 13

STOPPING DISTANCES:
How does weather or road surface affect braking distance?

Answer 13

if it is wet or icy, or there are leaves or oil on the road, there is less grip (and so less friction) between the vehicle’s tires and the road, which can cause the tires to skid

Question 14

STOPPING DISTANCES:
How can the condition of your tyres affect braking distance?

Answer 14

if the tyres of a vehicle are bald (they don’t have any tread left) then they cannot get rid of water in wet conditions, this leads to them skidding on top of the water

Question 15

STOPPING DISTANCES:
How can the condition of you brakes affect your breaking distance?

Answer 15

if they are worn or faulty they won’t be able to apply as much force as well-maintained brakes, which could be dangerous when you need to brake hard

Question 16

STOPPING DISTANCES:
Why is driving too close to other cars in icy condition dangerous?

Answer 16

icy conditions increase the chance of skidding (and therefore the stopping distance)

Question 17

STOPPING DISTANCES:
Why are speed limits so important?

Answer 17

speed has a large affect on the stopping distance

Question 18

STOPPING DISTANCES:
When do you need to leave more space in front of you in order to stop safely?

Answer 18

when you have a longer stopping distance

Question 19

STOPPING DISTANCES:
What happens when the brake pedal is pushed?

Answer 19

• the brake pads are pressed onto the wheels
• this contact causes friction, which causes work to be done
• the work done between the brakes and wheels transfers energy from the kinetic energy stores of the wheels to the thermal energy store of the brakes
• the brakes increase in temperature

Question 20

STOPPING DISTANCES:
Why is a greater braking force needed when a vehicle is travelling faster?

Answer 20

when a vehicle is travelling faster, it has more energy in its kinetic stores, so more work needs to be done to stop it
- this means a greater braking force is needed to make it stop within a certain distance

Question 21

STOPPING DISTANCES:
What do larger braking forces cause?

Answer 21

larger decelerations

Question 22

STOPPING DISTANCES:
Why can very large decelerations be dangerous?

Answer 22

• they may cause breaks to overheat (so they don’t work as well)
• or could cause the vehicle to skid

Question 23

REACTION TIMES:
What two values is the typical reaction time between?

Answer 23

0.2 and 0.9 seconds

Question 24

REACTION TIMES:
What 4 factors can affect reaction times?

Answer 24

• tiredness
• drugs
• alcohol
• distractions

Question 25

STOPPING DISTANCES: What is the typical stopping distance for a car travelling at 30 mph? - break this into thinking and braking distance? - how many car lengths is the total distance?

Answer 25

- 23 m - 9m = thinking distance - 14m = braking distance - 6 car lengths

Question 26

STOPPING DISTANCES: What is the typical stopping distance for a car travelling at 50 mph? - break this into thinking and braking distance? - how many car lengths is the total distance?

Answer 26

- 53 m - 15 m = thinking distance - 38 m = braking distance - 13 car lengths

Question 27

STOPPING DISTANCES: What is the typical stopping distance for a car travelling at 70 mph? - break this into thinking and braking distance? - how many car lengths is the total distance?

Answer 27

- 96m - 21m = thinking distance - 75 m = braking distance - 24 car lengths

Question 28

STOPPING DISTANCES: How can stopping distances help to avoid accidents?

Answer 28

the stopping distance is the amount of space the driver needs to leave between themselves and the car in front, so that if they needed to stop suddenly they would have time to do so safely

Question 29

STOPPING DISTANCES: What is 'enough space' between one car and another on the road?

Answer 29

the stopping distance for the speed they are going at

Question 30

STOPPING DISTANCES: Why are speed limits really important?

Answer 30

because speed affects the stopping distance so much

Question 31

STOPPING DISTANCES: What is the relationship between car speed and thinking distance?

Answer 31

they increase at the same rate (producing a linear graph)

Question 32

STOPPING DISTANCES: Why do thinking distance and speed increase at the same rate?

Answer 32

thinking time stays pretty constant,- but the higher the speed, the more distance you cover in the same time

Question 33

STOPPING DISTANCES: What is the relationship between braking distance and speed?

Answer 33

braking distance increases faster the more you speed up

Question 34

STOPPING DISTANCES: Why does braking distance increase faster the more you speed up?

Answer 34

- the work done to stop the car is equal to the energy in the car's kinetic energy store - as speed doubles, the kinetic energy increases 4-fold, and so the workdoen to stop the car increases 4-fold - since w=Fs and the breaking force is constant, the breaking distance increases 4-fold

Question 35

STOPPING DISTANCES: What does the graph for speed against stopping distance look loke?

Answer 35

a curved upwards graph from the origin steadily gets steeper