"If you fire a cannonball straight upwards with a starting speed of 40 m/s. How high does it go, and how long will it be in the air?"
All you need to do is change the value of the starting velocity in cell B7 to "-40" (40 m/s up) and read the results from the spreadsheet.
"What if the numbers aren't quite so "pretty"? For instance, if the projectile is launched upward with a speed of 14 m/s, how long will it be in the air?"
Changing the starting velocity in cell B3 gives:
Changing the time interval in cell B4 gives you a closer look: