Answer
The magnitude of the average velocity is $~~9.0~m/s$
Work Step by Step
The ball falls $5.20~m$ to the surface of the water and then falls $38.1~m$ to the bottom of the lake. The ball falls a total distance of $43.30~m$
The ball falls for a total time of $4.80~s$
We can find the average velocity:
$v_{ave} = \frac{\Delta y}{\Delta t} = \frac{43.30~m}{4.80~s} = 9.0~m/s$
The magnitude of the average velocity is $~~9.0~m/s$.
