Why does it not make sense? y= 40t- 16t^2= 24 is the same as 16t^2- 40t+ 24= 16(t- 1)(t- 1.5)= 0. The ball goes up to a maximum height at t= 1.25, then back downward. From t= 1 to t= 1.25, the velocity is positive. From t= 1.25 to t= 1.5, the velocity is negative. The average velocity is 0.