Calculating Stopping Distances Flashcards

All 6 cards in this deck

What is the equation for the work done by the brakes in bringing a vehicle to rest?

work done = braking force × braking distance

What are the steps to find a car's braking distance from its kinetic energy?

e.g. kinetic energy $=200\,000$ J, braking force $=10\,000$ N

1. Work done by the brakes = initial kinetic energy: $200\,000$ J.
2. Rearrange work done = braking force × braking distance: $d = \frac{W}{F}$.
3. $d = \frac{200\,000}{10\,000} = 20$ m.

How does braking distance depend on the initial speed of a vehicle?

Braking distance is proportional to speed squared ($d \propto v^2$), so doubling the speed makes it four times as long.

True or false? Doubling a car's speed doubles both the thinking distance and the braking distance.

False. Thinking distance doubles, but braking distance becomes four times as large.

Roughly what is the stopping distance of a car travelling at 30 mph (about 13 m/s) in good conditions?

About 23 m (roughly 9 m thinking + 14 m braking).

What shape is a graph of braking distance against initial speed for a car?

An upward curve through the origin, because $d \propto v^2$.