Explanation:
Since the ball was thrown horizontally, there will be no vertical component to its initial velocity. Once the ball is released, it will be subject to gravity and will accelerate downward until it reaches the bottom. What you're most interested in is how long the ball was in the air until it hit the ground. To figure this out use the following formula:
d = 1/2*g*t^2
Since you're dealing in meters, g is 9.8.
54 = 4.9*t^2
t^2 = 54/4.9
t = 3.3 seconds.
Now you know how long it took for the ball to reach the ground. It traveled 35 meters in that time.
Rate = Distance/Time
So your horizontal speed (which is also the initial speed since we assume no air friction throughout the trajectory) will be
35 m / 3.3 sec
= 10.5 m/sec
Hope this helps.
