Answer: The angular acceleration of the merry-go-round is 0.4 rev/s^2. We can use the following equation to find the final angular velocity:
ω_f = ω_i + αt
where ω_f is the final angular velocity, ω_i is the initial angular velocity (which is zero in this case), α is the angular acceleration, and t is the time.
Substituting the given values, we get:
ω_f = 0 + (0.4 rev/s^2)(6 s)
ω_f = 2.4 rev/s
Therefore, the rotational velocity of the merry-go-round after 6 s is 2.4 rev/s.