Forces in Motion

YOU ARE LEARNING:

Stopping Distance

When we are driving a car and see something that makes us come to a stop, this stopping distance covered can be calculated depending on different factors.

Imagine a driver is travelling down a country road at $30\space mph$ . He notices a stationary lorry ahead blocking his path. The lorry is approximately 30 metres in the distance. What should the car driver do?

If the car is travelling at $30\space mph$ , it will take the vehicle some distance to come to a complete stop after the driver has noticed the hazard and applied the brakes. Try to guess the typical distance it would take.

The stopping distance is the distance it takes to bring a vehicle to a complete stop in an emergency. It may be longer than you expect, because it includes the distance it takes for the driver to react, and the distance it takes for the car to stop once the braking force is applied.

The thinking distance is how far the car travels during the driver's reaction time. If a driver is tired or has been drinking alcohol, how will this affect the thinking distance?

If the braking distance is the distance the vehicle takes to stop under the braking force, which factors might increase the braking distance? Pick all the options you think are correct.

You can select multiple answers

For a car travelling at $30\space mph$ , the typical thinking distance is $9\space m$ , the typical braking distance is $14\space m$ and the typical stopping distance is $23\space m$ . How would you describe the relationship between the three distances?

If the stopping distance is the overall distance it takes a vehicle to stop, it must be the sum of the thinking distance and the braking distance: $thinking \space distance + braking \space distance = stopping \space distance$

There is one important factor which affects both thinking and braking distance. Can you work out what it is from the examples you have already seen?

A driver is travelling at $60\space mph$ on a motorway and has to perform an emergency stop. The driver's thinking distance is $18\space m$ , and the car's braking distance is $55\space m$ . What is the overall stopping distance of the car?

The image shows typical stopping distances at different speeds. For every speed increase of $10\space mph$ , by how many metres does the thinking distance increase?

If a car is travelling at $40\space mph$ , how much distance should the driver leave between himself and the car in front of him at the very least? Give your answer in metres.

Try to estimate the typical stopping distance for a car travelling at $70\space mph$ .

A) $80\space m$

B) $110\space m$

C) $96\space m$

Answer A, B or C.

Do you think that a lorry would have the same stopping distance as a car under the same conditions?

The mass of a vehicle does not affect thinking distance, but it does affect braking distance. A vehicle with more mass will have a greater braking distance, and therefore a greater overall stopping distance.