Explanation:
We need to calculate the centripetal force:
Fc = W + F
With Fc being the centripetal force, W the weight of the boy, F the centrifugal force (apparent).
We know that we can calculate the apparent centrifugal force thank to the formula:
F = (m·v²)/r = 204N
So we can write:
Fc = W + F = 445N + 204N = 649N