8.4 On the road

Question 1

What is thinking distance

Answer 1

The distance travelled by a vehicle in the time it takes the driver to react.

Question 2

Thinking distance calculation

For a vehicle moving at constant speed v, thr thinking distance s1 =

Answer 2

speed * reaction time

Question 3

What affects reaction time

Answer 3

Distractions
Drugs
Alcohol

Question 4

What is braking distance

Answer 4

The distance travelled by a car in the time it takes to stop safely from when the brakes are first applied

Question 5

Braking distance calculation

Assuming constant deceleration, a, to zero speed from speed u

Answer 5

Braking distance s2 = u^2/2a

Question 6

What is stopping distance

Answer 6

thinking distance + braking distance

Question 7

How does skidding happen

Answer 7

If the driver tries to accelerate too fast, the wheels skid as there is an upper limit to the amount of friction between the tyres ad the road
When the brakes are applied the wheels are slowed down by the brakes, the vehicle therefore slows down provided the wheels do not skid. If the upper limit of friction is reached, it will skid

Question 8

What are most vehicles fitted with

Answer 8

ABS - Anti-lock brake system, which consists of a speed sensor on each wheel linked to a central electronic control unit that controls hydraulic valves in the brake system. When the brakes are applied and the wheels start to lock, the control unit senses that it is rotating more slowly so the valves are activated so brake pressure is reduced to prevent locking

Question 9

Investigating friction

Answer 9

Measure limiting friction between the underside of a block and the surface its on.
Pull block with increasing force until it slides.
Limiting frictional force on block is equal to the pull force on the block just before sliding occus

Question 10

What does braking distance depend on

Answer 10

Speed of vehicle at the instant the brakes are applied
On the road conditions
On condition of the vehicle tyres

Question 11

When is skidding more likely

Answer 11

On a greasy or icy road

As the limiting frictional force between the road and the tyres is reduced from its dry value.

Question 12

How to stop a vehicle safely on a greasy or icy road

Answer 12

Brakes must be applied with less force than on a dry road otherwise skidding will occur

Question 13

Why must tread on a tyre must not be less than a certain depth

Answer 13

Or else any grease, oil or water on the road reduces the friction between the road and the tyre very considerably