Answer:
The magnitude of the final velocity of the water balloon is 84.3 m/s.
Step-by-step explanation:
To calculate the velocity of the water balloon when it strikes the ground we need to use the next equation:

Where:
: is the final velocity =?
: is the initial velocity = 2 m/s
g: is the gravity = 9.81 m/s²
h: is the height = 4.5 m
By entering the above values into equation (1) we have:

The minus sign is because the direction of the velocity vector is in the negative vertical axis.
Therefore, the magnitude of the final velocity of the water balloon is 84.3 m/s.
I hope it helps you!