Q5 Q19 Choose the correct formula for the displacement d from the rest position of the object attached to the spring at time t.

t=0, d=0 so ans B is wrong
t=0, dd/dt <0 as it is propelled downward so ans C is wrong
ang vel = 2[tex] \pi [/tex] / period
= 2[tex] \pi [/tex] / 4.5
= 4[tex] \pi [/tex] / 9
so D is the correct answer