23.如圖①,在矩形ABCD中,AB=8,AD=4.點(diǎn)P從點(diǎn)A出發(fā),沿A→D→C→D運(yùn)動(dòng),速度為每秒2個(gè)單位長(zhǎng)度;點(diǎn)Q從點(diǎn)A出發(fā)向點(diǎn)B運(yùn)動(dòng),速度為每秒1個(gè)單位長(zhǎng)度.P、Q兩點(diǎn)同時(shí)出發(fā),點(diǎn)Q運(yùn)動(dòng)到點(diǎn)B時(shí),兩點(diǎn)同時(shí)停止運(yùn)動(dòng),設(shè)點(diǎn)Q的運(yùn)動(dòng)時(shí)間為t(秒).連接PQ、AC、CP、CQ.
(1)點(diǎn)P到點(diǎn)C時(shí),t=
;當(dāng)點(diǎn)Q到終點(diǎn)時(shí),PC的長(zhǎng)度為
;
(2)用含t的代數(shù)式表示PD的長(zhǎng);
(3)當(dāng)三角形CPQ的面積為9時(shí),求t的值.