Program 2, CS 101, Prof. Loftin

Due Monday, February 23, 2004

The problem

A moving car is being braked at a constant acceleration. Compute whether or not the car has come to a complete halt. Read $v_0$ (the initial velocity), $a$ (the acceleration--which is negative to represent braking), and $t$ (the amount of braking time) from the keyboard. Use appropriate prompts to for each of these. You should note in your prompts that $v_0$ and $t$ should be positive, and $a$ should be negative. If the quantity $t\vert a\vert$ ($t$ times the absolute value of $a$) is greater than or equal to the initial velocity $v_0$, the car has come to a complete stop; otherwise the final velocity is $v_0+at$. Print the final velocity or the message, ``The car has come to a complete stop."

Next, your program should print out the distance the car has travelled while braking. If the car has come to a complete stop, this distance is given by

$$\frac{v_0^2}{2\vert a\vert}.$$

On the other hand, if the car has not come to a complete stop, the distance the car has travelled is given by

$$v_0t+\frac{at^2}2.$$

Sample runs

Here are two sample runs of my program:

 <pegasus> a.out
 Enter an initial velocity (a positive number): 10
 Enter an acceleration for braking (a negative number): -2
 Enter the time allowed for braking (a positive number): 3

 The final velocity is 4.
 The distance the car has travelled while braking is 21.
 <pegasus>

 <pegasus> a.out
 Enter an initial velocity (a positive number): 8
 Enter an acceleration for braking (a negative number): -5
 Enter the time allowed for braking (a positive number): 2

 The car has come to a complete stop.
 The distance the car has travelled while braking is 6.4.
 <pegasus>

How to do it

You should use an if else statement to separate the two cases.

Hints

The square of a number x may be represented by x * x or by pow(x,2). (The function pow is contained in the header file math.h or cmath.)

The variables $v_0$, $a$ and $t$ should be double type. Recall that the absolute value of a double variable v0 is given by fabs(v0). You will need to include one of the header files math.h or cmath to use the function fabs. You probably also want to use variables v_final and dist to represent the final velocity and the distance travelled while braking.

Handing in your program

To be announced.

Program requirements

Your program must compile on pegasus using our usual g++ compiler.

Programs which do not compile will not be graded. Your program should be documented with meaningful variable names, and comments where necessary. Your program should begin with a comment giving your name and a brief description of the program. Your program must contain:

• Meaningful prompts for the user to enter the initial velocity, acceleration and time. These should include instructions that the initial velocity and time should be positive, and the acceleration should be negative.
• You may assume the user will follow these instructions (so you do not have to print an error message if for example the user enters a positive number for the acceleration).

Running my solution

You can run my solution by typing

~loftin/cs101/solution2

at the <pegasus> prompt.