Sorin hits a cricket ball straight up into the air. after 1.5s the ball is falling straight down with a speed of 6.5m we want to find the initial vertical velocity of the ball. we can ignore air resistance.
which kinematic formula would be most useful to solve for the target unknown?

Explanation:

The vertical velocity of an object in free fall is given by:

where

v0 is the initial vertical velocity

a is the acceleration, which actually corresponds to (gravitational acceleration, with downward direction)

t is the time

So the explicit formula would be

And we can re-write it to find the initial vertical velocity:

For our problem, we have

v(t) = -6.5 m/s (with negative sign since the ball is falling downward)

t = 1.5 s

Substituting, we find

in the upward direction.

asthenosphere and convection