In order to determine the maximum initial velocity, use the following formula for the maximum height that an object reaches:
![h=(v^2_o)/(2g)](https://img.qammunity.org/2023/formulas/physics/college/ls740jpyz54bbrfdsnsqsvgek7xbzqpt7t.png)
where,
vo: maximum intial velocity = ?
g: gravitational acceleration constant = 9.8 m/s^2
h: maximum height = 20 m - 1.5 m = 18.5 m
Look that h has been taken regarding with where the ball was thrown.
Solve for vo in the previous formula and replace the values of the oher parameters, as follow:
![v_o=\sqrt[]{2gh}=\sqrt[]{2(9.8(m)/(s^2))(18.5)}\approx19.04(m)/(s)](https://img.qammunity.org/2023/formulas/physics/college/fn2vgj3igu5cq0eont4nwv2yr07rohbzj4.png)
Hence, the maximum initial velocity should be approximately 19.04 m/s