1.12 Stopping safely

Question 1

How are speed and thinking distance related proportionally?

Answer 1

Speed is directly proportional to thinking distance

E.g. if speed doubles, thinking distance doubles, as reaction time is constant, but you travel twice the distance in that time

Question 2

How are braking distance and speed related?

Answer 2

Braking distance increases faster the more you speed up.

This is as it depends on the kinetic energy, which is proportional to velocity squared. So double the speed results in 4x the braking distance

Question 3

Give typical thinking and braking distances at 30mph, 50mph and 70mph

Answer 3

30mph: 9m thinking, 14m braking

50mph: 15m thinking, 38m braking

70mph: 21m thinking, 75m braking

Question 4

How does “work done” relate to braking?

Answer 4

Work done by the brakes to stop the car equals the kinetic energy store of the car before the brakes were applied

Question 5

What equation relates work done by the brakes to kinetic energy of a vehicle?

Answer 5

1/2 * m * v^2 = F * d

m = mass(kg)
v = speed(m/s)
F=force (N)
d = braking distance (m)

The LHS is the kinetic energy

Question 6

CARRY ON FROM PAGE53 OF THE BOOK