Calculate: A ball is dropped from a cliff and has an accerleration of 9.8 m/s2 how long will it take the ball to reach a speed of 24.5 m/s?

When you say "acceleration of 9.8 m/s²", that means that the object is speeding up, and its speed ... at any instant ... is 9.8 m/s faster than it was 1 second earlier.

When the ball is dropped, its speed starts out zero. After 1 second, it's falling at 9.8 m/s. After 2 seconds, its speed has grown to 19.6 m/s. After 3 seconds, its speed is 29.4 m/s. We're looking for 24.5 m/s, so we know that it'll be some time between 2 sec and 3 sec.

The question to ask is: "How many times does it add on another 9.8 m/s of speed before it reaches 24.5 m/s?". The reason for asking it that way is it sounds exactly like a division problem, and that's exactly the way to answer it.

(24.5 m/s) / (9.8 m/s²) = 2.5 seconds