Answer: -39.2 m/s
Step-by-step explanation:
As soon as the rock leaves the tourist's hand, it will be in freefall. Since the rock will have a constant acceleration, we can use a kinematic equation to solve it.

Because the rock starts from rest, we know the initial velocity:

Since the only force acting on the rock is gravity, we know that the only acceleration will be acceleration due to gravity:

And we are given the time:

We can simply plug these values into the kinematic equation to get the rock's velocity at 4.0 seconds:
