Design due: Thursday, January 25th at the beginning of class
Program due: Tuesday, Jan 30th by 11:59 PM
Getting Started
Start by downloading CS101_Assign01.zip, saving it in the directory CS101 within your home directory.
If you are on Windows, start a Cygwin Bash Shell and run the following commands:
cd h:
cd CS101
unzip CS101_Assign01.zip
cd CS101_Assign01
If you are on Linux, start a terminal and run the following commands:
cd CS101
unzip CS101_Assign01.zip
cd CS101_Assign01
Using Notepad++ (or a Linux text editor such as Pluma), open the file
CS101/CS101_Assign01/Freefall.cpp
You will add your code to this file.
When you are ready to compile the program, in the Cygwin bash shell (or Linux terminal) window type the command
make
To run the program, type the command
./Freefall.exe
Your Tasks
Design
Based on the requirements described below in the “Program” section, fill out a design template. Consider what the input and output of the program are, and what steps are necessary to compute the output from the input.
The design is due at the beginning of class on Thursday, January 25th.
Program
Your task is to write a program that prompts the user to enter the height of an object dropped from rest (neglecting air resistance). The program should then print out the object’s time to fall to the ground and velocity at impact in several different units including
- meters/sec
- ft/sec
- miles per hour
Here is an example run of the program (user input in bold):
Enter the initial height of the object in meters: 50
The object took 3.19 seconds to fall.
The velocity of the object at impact was: 31.3 m/sec
102.7 ft/sec
70.1 mph
The time field should have two decimal places of precision. All of the velocity values should allow for up to four digits in front of the decimal point and one digit after the decimal point such that the decimal points are aligned in the final output.
Hints
Physics
The basic physics (which many of you will learn this semester in PHY160) governing an object falling only under the influence of gravity (neglecting air resistance) is integration of the acceleration (which for the earth is -9.81 m/s2) with respect to time. Hence the velocity of the object as a function of time is given by
where v(t) is the velocity at time t, a is the acceleration due to gravity (-9.81 m/s2), and v0 is the initial velocity (which for this assignment is 0).
The position of the object as a function of time is found by integrating the velocity with respect to time as follows
where x(t) is the position at time t and x0 is the initial position (which for this assignment is the value entered by the user).
Therefore we can find the time the object falls in seconds by solving the above equation for t setting x(t) = 0, a = -9.81, v0 = 0
where x0 is given in meters. Once the time is computed, the velocity at impact is computed from the velocity equation as (again setting v0 and a = -9.81)
Note the velocity will be negative indicating the object is moving downward, but your output should only show the positive magnitude.
Some useful conversions
- 3.28 feet in a meter
- 3600 seconds in an hour
- 1609 meters in a mile
USE the computer to compute the conversion factors for the velocity units by simply writing expressions in your program and storing the results in variables.
Programming
START EARLY! And develop the program incrementally! You should always have a working program at each step (even if only minimally) to make it easier to debug errors. For example, make sure the program obtains the user input properly and then add one computation at a time. Also make sure you follow good programming practices such as adding comments, using meaningful variable names, and having proper indentation in the program.
The square root function in C is
sqrt(x)
which returns a double value which is the square root of x. You will need to include the math.h library by adding the following line at the top of your program
#include <math.h>
See pages 346–353 of the textbook for details regarding the conversion specifiers for printf.
Grading
The overall assignment is out of 100 points.
Design:
The design is worth up to 15 points. The design will be graded for effort rather than correctness, so if you make a good faith effort, you should receive full credit for the design. However, if your design is not correct, it will be difficult to implement the program. We will go over a correct design in class on the day the designs are due, and it is likely that you will receive feedback on your design if you meet with your instructor or a tutor to get help on the assignment.
Program:
- Obtaining user input and correctly computing the time is worth up to 55 points
- Above, and computing the final velocity in m/s is worth up to 65 points
- Above, and computing the final velocity in ft/s and mph is worth up to 75 points
- Above, and output formatted correctly is worth up to 85 points
Submitting
Your design will be collected in class on the day that designs are due.
To submit your program, make sure your Freefall.cpp file is saved, and in the Cygwin window type the command
make submit
Enter your Marmoset username and password (which you should have received by email.) Note that your password will not be echoed to the screen. Make sure that after you enter your username and password, you see a message indicating that the submission was successful.
If the make submit command does not work, you can submit using the web interface (see the link for details).
Make sure that you check the file(s) you submitted to ensure that they are correct. See the instructions for Verifying your submission.
