What is the ball's centripetal acceleration?

Question

A child attaches a rubber ball to a string and whirls it around in a circle overhead. If the string is 0.2 m long and the ball's speed is 16 m/s, what is the ball's centripetal acceleration?

Answer 1

a_c = v² / r

v = 16 m/s

r = 0.2 m

Plug in the numbers and get a_c in units of m/s².