Question

A flea jumps straight up to a maximum height of 0.540 m . what is its initial velocity v0 as it leaves the ground?

Answer 1

For an uniformly accelerated motion, we can write
$2ah=v_f^2-v_0^2$
where $a=g=-9.81 m/s^2$ is the acceleration of this motion, which in this problem is the gravitational acceleration, with a negative sign because it points downward, against the direction of the motion; h=0.540 m is the distance covered by the flea, and $v_0$ is the initial velocity. 

At the maximum height, the velocity is zero, so $v_f =0$. Therefore we  can solve to find $v_0$:
$v_0 = \sqrt{2ah}= \sqrt{2(9.81 m/s^2)(0.540 m)} =3.25 m/s$