Question

A tennis ball is thrown horizontally at a speed of 10 m/s from the top of a building 78.4 meters high. How long does it take the ball to hit the street?

Answer 1

Hint:
The answer has nothing to do withe the 10 m/s horizontal velocity com[ponent.

Just calculate how long it takes for an object to fall 78.4 m

Y = (1/2) g t^2

(ignoring air resistance)

Solve for t.

Answer 2

Exactly as long as it takes to fall 78.4 meters since it had zero initial vertical velocity (only horizontal).
(1/2)(9.8) t^2 = 78.4