Question

When a rock thrown straight up reaches its maximum height, its velocity is?

Answer 1

Using kinematic equation,
V² - U² = -2ah (minus g is in downward direction)
At highest point, final velocity will be zero. i.e V = 0.
∴ -U² = -2ah
U = √2gh (where a = g and h = maximum height achieved)

You can find velocity if h is given to you.