Example programming problem about braking distance

This section examines how to take a problem, decompose it and design an algorithm to solve it.

The following example has been taken from an AQA past paper. It reflects the type of question that may appear in an exam paper.

The problem

A programmer has been asked to design a program that calculates an estimate of the braking distance in metres for a new model of go-kart that is travelling between 10 and 50 kilometres per hour - km/h.

The program should keep asking the user to enter a speed for the go-kart until they enter a speed between 10 and 50 km/h. The braking distance in metres is calculated by dividing the speed by 5. The user should then be asked if the ground is wet and the braking distance should be multiplied by 1.5 if this is true. Finally, the program should output the calculated braking distance.

Decompose the problem

The first step is to break down - decompose - the overall problem into several smaller, more easily solved problems:

Find out the speed of the go-kart.
Validate the data entered is correct.
Find out if the ground is wet.
Work out which calculation to use for braking distance.
Calculate the braking distance.
Output the braking distance.

Variables and constants

From the above, the solution will require the following . These values will change as the program is run.

Variable	Data type
`speed`	Integer
`wet_ground`	String/Boolean*
`braking_dist`	Integer

Variable	`speed`
Data type	Integer

Variable	`wet_ground`
Data type	String/Boolean*

Variable	`braking_dist`
Data type	Integer

*As user input is used here, a is valid as they may answer yes/no.

The following will be used. These values will not change when the program is run.

Constant	Data type
`wet_calc`	Real

Constant	`wet_calc`
Data type	Real

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Decomposition and algorithm practice questions - AQAExample programming problem about braking distance