What is the forward velocity of a 250 lb stone projectile that leaves a medieval catapult 55 degrees from the ground at 50 m/s?

28.5 m/s

Explanation:

The speed has two orthogonal components, horizontal and vertical. To decompose the speed into these components we can use these trigonometric equations:

Vh = V * cos(a)

Vv = V * sin(a)

The forwards velocity is the horizontal component, so we use

Vh = V * cos(a)

Vh = 50 * cos(55)

Vh = 50 * 0.57

Vh = 28.5 m/s