Question

6. The Highway Code says that at 20 m/s, the

reacting (thinking) distance of a driver is 14 m,
and the brakes take 3 seconds to halt the car.
a) What is the reaction time in this case?
b) Plot a velocity-time graph for these data
(assume the brakes are on steadily for 3 s).
c) Use the graph to estimate the speed at
which the driver would hit a wall 3
seconds after first noticing it.

Answer 1

Answer:a) The reaction time can be calculated by dividing the reacting distance by the velocity:

Reaction Time = Reacting Distance / Velocity

Reaction Time = 14 m / 20 m/s

Reaction Time = 0.7 seconds

b) To plot a velocity-time graph, we can assume that the velocity remains constant at 20 m/s until the driver applies the brakes. Then, the velocity decreases linearly to zero over a period of 3 seconds.

The graph would have the following characteristics:

The velocity remains constant at 20 m/s for the initial time.

After 3 seconds, the velocity decreases linearly to zero.

The graph would be a horizontal line at 20 m/s for the first 3 seconds and then a straight downward line reaching zero velocity at the end of the 3-second period.

c) Since the graph shows a linear decrease in velocity, we can estimate the speed at which the driver would hit a wall 3 seconds after first noticing it by looking at the velocity at that time.

From the graph, at 3 seconds, the velocity would be zero, indicating that the car would have come to a complete stop. Therefore, the estimated speed at which the driver would hit the wall is 0 m/s.

Step-by-step explanation: