Projectile Motion (freeware)
by Daniel Bishop, June 2000
danb2k@hotmail.com or danb_83@yahoo.com

How to use this program:

1. Run prgmPROJMOT.

2. Enter a value for G, the acceleration due to gravity.  Usually, this will be 9.8.

3. Enter a value for V, the initial speed of the projectile.

4. Enter a value for theta, the angle at which the projectile is fired.

5. Enter a value for Y0, the initial height of the projectile.

6. The calculator will now draw the projectile's path.  After it is finished, you can use the left and right arrow keys to trace the graph.

7. Press ENTER.  The calculator will now display the number of seconds it takes for the projectile to hit the ground (T), and the maximum height of the projectile.

Frequently asked questions:

Q.  Why do I have to enter G?  Why doesn't this program "know" that g=9.8 m/s²?
A.  Some teachers want you to assume that g=10 instead of 9.8.  Also, you may need to use non-SI units (g=32 ft/s²) or find a projectile's path on another planet (or on the moon where g=1.63 m/s²).  By entering the value of g at a prompt, you don't need to edit the program to use a different g.

Q.  What are the valid values for theta?
A.  -90° (straight down) < theta < 90° (straight up)
Notice that those are <'s and not <='s.  Entering a value outside this range causes a window range error.

Q.  What if the projectile is thrown straight up?
A.  This program won't work.  In this case, use this formula instead:  Y=VT-GT²/3.

Q.  Are the calculations affected by whether my calculator is in Degree or Radian mode?
A.  Yes

Q.  Is Y0 the same as the Y0 function?
A.  No, that's just a prompt.  The initial height is stored in a real variable.

Q.  The projectile's path is distorted.
A.  The horizontal scale is exaggerated if theta is very large in magnitude.

Q.  The graph takes too long to draw.  How can I speed it up?
A.  Increase Tstep.

Q.  I need to know how long it takes the projectile to reach a point other than the ground.
A.  Set up the coordinates so that the Y-coordinate of the final position is zero.

Q.  How do I find the projectile's speed at a point after T=0?
A.  Horizontal speed = V * cos(theta)
    Vertical speed = V * sin(theta) - G * T
    speed = sqrt((horizontal speed)² + (vertical speed)²)