Answer:
R = 1.8 m
Step-by-step explanation:
This is a simple harmonic movement exercise, at the bottom of the swing the acceleration is vertical upwards and the speed is tangential to the trajectory, that is horizontal; the expression for the centralized acceleration is
= v² / R
R = v² /a_{c}
where the radius is equal to the length of the swing
let's calculate
R = 8.1 / 4.5
R = 1.8 m