When a pendulum $0\mathrm{.}5$ m long swings back and forth, its angular displacement $$ from rest position, in radians, is given by $()=1/4$sin$($pi$/2$ t$)$

$,$ where t is the time, in seconds. At what time$($s$)$ during the first $4$ s is the pendulum displaced $1$ cm vertically above its rest position? $($Assume the pendulum is at its rest position at t $=0.)$