A stone is thrown upwards on Earth with an initial speed of $18\frac{m}{s}.$ The following students are arguing over how $($or if$)$ the time in the air can be determined. Hansel: The time cannot be determined because we do not know the height to which the stone travels.

Gretel: The time cannot be determined because we do not know the rate at which the stone slows down $($i$.$e$.,$ the acceleration$).$

Jack: Actually we can determine the time, because we know the stone slows down at $9\mathrm{.}8\frac{m}{s}\frac{?}{s},$ so we just take the $18\frac{m}{s}$ and divide by $9\mathrm{.}8.$ Jill: No$,$ Jack, that would only tell us the time it takes to get to the top. We would need to multiply by two, because it takes the same amount to fall down.

Which student seems to have the most complete grasp of the situation?

Jack

Gretel

Hansel

Jill