Motion and Safety

Question 1

How can you measure human reaction times?

Answer 1

• Using the ruler drop test
• Person A and B hold each end of a ruler with 0cm mark at the bottom
• Person A drops the ruler without telling person B
• Person B catches it
• The distance travelled corresponds to their reaction time

Question 2

Why is it important that the 0cm mark is at the bottom?

Answer 2

So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for

Question 3

What is the stopping distance of a vehicle equal to?

Answer 3

The sum of thinking distance and braking distance

Question 4

For a given braking distance, if the vehicles speed is increased, what can be said about its stopping distance?

Answer 4

The stopping distance is increased with an increase in speed

Question 5

Give a typical range of values for human reaction time.

Answer 5

0.2 seconds - 0.9 seconds

Question 6

Give three factors which can affect a drivers reaction time.

Answer 6

1. Tiredness
2. Drugs
3. Alcohol

Question 7

Give two factors which may affect braking distance.

Answer 7

1. Adverse (wet/icy) road conditions
2. Poor tyre/brake conditions

Question 8

Describe the energy transfers that take place when a car applies its brakes.

Answer 8

• Work is done by the friction force between the brakes and wheel
• Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs

Question 9

To stop a car in a given distance, if it’s velocity is increased, what must happen to the braking force applied?

Answer 9

The braking force must also be increased

Question 10

State two consequences of a vehicle undergoing very large decelerations.

Answer 10

1. Kinetic energy converted to heat is very high causing brakes to overheat
2. Loss of control of the vehicle