Answer: The velocity of the kid is 5.6 m/s
Explanation: Ok, the velocity of the kid will be:
v = w*r
where r is the radius, and w is the frequency.
We know that the diameter is 18m, and the diameter is equal to two times the radius. So r = 18m/2 = 9m
Now, we know that the circumference of a circle is equal to c = 2pi*r, so each revolution has this length, if the kid does 5.9 revolutions in one minute, then the kid spins at v = 5.9*2pi*9m/min
But we want to write this in meters per second, this means that we need to divide it by 60.
v = (5.9*2pi*9/60)m/s = 5.56 m/s