Forces and breaking (5.6.3)

Question 1

What is the thinking distance?

Answer 1

the distance the vehicle travels during the driver’s reaction time

Question 2

What is the braking distance?

Answer 2

the distance the vehicle travels under the braking force

Question 3

What is the stopping distance?

Answer 3

the sum of the thinking and braking distance

Question 4

For a given braking force the greater the speed of the vehicle, the (…) the stopping distance.

Answer 4

greater

Question 5

The speed and stopping distance are in a (…) relationship. What does this mean?

Answer 5

non-linear

The rate of stopping distance will be greater than the rate of change of speed (useful for estimating stopping distances)

Question 6

What does a stopping distance graph look like?

Answer 6

A horizontal bit for the thinking distance, when speed doesn’t change, then a downward sloping line representing the deceleration.

Question 7

How do you calculate the total stopping distance from a velocity-time graph?

Answer 7

find the area under the graph

Question 8

Reaction times (…) from person to person

Answer 8

vary

Question 9

What is the typical range of values for human reaction times?

Answer 9

0.2s to 0.9s

Question 10

4 needed

What may the drivers reaction times be affected by?

Answer 10

• tiredness
• drugs
• alcohol
• distractions

Question 11

Describe a simple method to measure human reaction times

Answer 11

• Drop a ruler 0.5m above and between someone’s open thumb and forefinger without warning
• The higher the reaction time needed to grasp the falling ruler, the further the ruler falls before being stopped.

Question 12

3 needed

What are factors that affect the braking distance of a vehicle?

Answer 12

• adverse road conditions
• weather conditions
• poor condition of the vehicle

Question 13

Adverse road conditions include…

Answer 13

wet or icy conditions

Question 14

Poor condition of the vehicle includes…

Answer 14

the vehicle’s brakes or tyres

Question 15

What is a safety implication of having too short braking distance for fast car?

Answer 15

The faster a vehicle travels, the greater the braking force needed to stop it in a certain distance.

A greater braking force produces a greater deceleration.

Large decelerations may cause the brakes to overheat, and the driver may also lose control of the vehicle.

Question 16

The distance required for road vehicles to stop in an emergency (…) with greater speed

Answer 16

increases

e.g.. a wet road condition may cause an increase braking distance of 30m for 30mph, but 50 for 60mph

Question 17

What is the typical thinking/braking/stopping distance for 20mph?

Answer 17

• thinking distance = 6 m
• braking distance = 6 m
• total stopping distance = 12 m

Question 18

What is the typical thinking/braking/stopping distance for 40mph?

Answer 18

• thinking distance = 12 m
• braking distance = 24 m
• total stopping distance = 36 m

Question 19

What is the typical thinking/braking/stopping distance for 70mph?

Answer 19

• thinking distance = 21 m
• braking distance = 75 m
• total stopping distance = 96 m

important note: thinking distance is proportional to speed, braking distance is not

Question 20

How does an object slow down when the brakes are applied?

Answer 20

When a force is applied to the brakes of a vehicle, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes (and surroundings) increases

Question 21

The greater the speed of a vehicle the (…) the braking force needed to stop the vehicle in a certain distance

Answer 21

greater

Question 22

The greater the braking force the (…) the deceleration of the vehicle

Answer 22

greater

Question 23

What may large declarations lead to that may pose risk to the driver?

Answer 23

brakes overheating and/or loss of control

Question 24

The amount of work that needs to be done by the brakes is (…) the kinetic energy of the vehicle

Answer 24

equal to