Answer:
u = 7.91 m/s
Step-by-step explanation:
It is given that,
Height from which a ball is launched is 3.2 m
It strikes the ground 4.1 meters away
We need to find the initial velocity of the ball. When the ball strikes the ground, its final velocity is equal to 0. Let u is the initial velocity. Using the conservation of energy as follows :

Hence, the initial velocity of the ball is 7.91 m/s. Yes, a stopwatch be a reasonable device for measuring the time this takes.