P3c: Forces and motion

Question 1

Force equation

Answer 1

force = mass × acceleration

Question 2

Thinking distance

Answer 2

distance travelled between the need for braking occurring and the brakes starting to act

Question 3

Braking distance

Answer 3

the distance taken to stop once the brakes have been applied

Question 4

Stopping distance

Answer 4

thinking distance + stopping distance

Question 5

Implications of stopping distances in road safety (3)

Answer 5

have different speed limits for different types of roads and locations as speed affects stopping distance

slow down when road conditions are poor

avoid driving too close to car in front so to ensure enough space to account for stopping distance

Question 6

Factors increasing thinking distance (4)

Answer 6

driver tiredness - increases reaction time and distance travelled

influence of alcohol or other drugs - increases reaction time and distance travelled

higher speed means more distance travelled during reaction time

distractions or lack of concentration - increases reaction time and distance travelled

Question 7

Factors increasing braking distance (4)

Answer 7

higher speed - more kinetic energy to be absorbed, which takes a longer time and increased distance while braking (squared relationship)

worn out brakes - less retarding force, less friction between brake and wheel, less deceleration, increased time to stop, increased distance travelled while braking

road conditions - ice/oil spills reduces friction between tyres and road, so there is less deceleration, increased time to stop, increased distance travelled while braking

increased car load means increased mass, reduced deceleration, increased time to stop, increased distance travelled while braking

Question 8

How does thinking distance and braking distance vary with speed(2)

Answer 8

increased speed causes thinking distance to increase linearly
(-speed doubles causes thinking distance to double)

increased speed causes braking distance to increase as a squared relationship
(-speed doubles causes thinking distance to quadruple)