Question

You throw a rock straight up into the air with a speed of 14.2 m/s. how long does it take the rock to reach its highest point?

Answer 1

The acceleration of gravity on or near the Earth's surface is 9.8 m/s² downward.
Is that right ?           I don't hear any objection, so I'll assume that it is.

That means that during every second that gravity is the only force on an object,
the object either gains 9.8m/s of downward speed, or it loses 9.8m/s of upward
speed.   (The same thing.)

If the rock starts out going up at 14.2 m/s, and loses 9.8 m/s of upward speed
every second, it runs out of upward gas in (14.2/9.8) = 1.449 seconds (rounded)

At that point, since it has no more upward speed, it can't go any higher.  Right ?

(crickets . . .)