Can someone help me ?

(a)
Period, T
= (5 s) / 20
= 0.25 s

(b)
Frequency, f
= (20) / (5 s)
= 4 Hz

(c)
Speed, v
= 2π(2 m)/(0.25 s)
= 50 m/s

(d)
Centripetal acceleration
= v²/r
= (50 m/s)²/(2 m)
= 1250 m/s²

(e)
Force acting on the rock to keep it in UCM
= Centripetal force
= mv²/r
= (0.005 kg)(50 m/s)²/(2 m)
= 6.25 N