A student fires a cannonball horizontally with a speed of 21m/s from a height of 55m. Neglect drag. what was the cannon balls initial vertical speed

0 m/s

Explanation:

The cannonball was launched horizontally, which means that it had no vertical distance and utterly no vertical speed. If you separate diagonal speed into components, the vertical component would be 0.

The cannonball would go in a sad little arc from 90 degrees, accelerating lower and lower due to gravity.