如圖,在平面直角坐標(biāo)系中,直線y=-
x+4與x軸交于點(diǎn)A,與y軸交于點(diǎn)B,點(diǎn)P從點(diǎn)O出發(fā)沿OA以每秒1個(gè)單位長的速度向點(diǎn)A勻速運(yùn)動(dòng),到達(dá)點(diǎn)A后立刻以原來的速度沿AO返回;點(diǎn)Q從A出發(fā)沿AB以每秒1個(gè)單位長的速度向點(diǎn)B勻速運(yùn)動(dòng),當(dāng)點(diǎn)P、Q運(yùn)動(dòng)時(shí),DE保持垂直平分PQ,且交PQ于點(diǎn)D,交折線QB-BO-OP于點(diǎn)E.點(diǎn)P、Q同時(shí)出發(fā),當(dāng)點(diǎn)Q到達(dá)點(diǎn)B時(shí)停止運(yùn)動(dòng),點(diǎn)P也隨之停止,設(shè)點(diǎn)P、Q運(yùn)動(dòng)的時(shí)間為t秒(t>0).
(1)點(diǎn)Q的坐標(biāo)是(
,
)(用含t的代數(shù)式表示);
(2)當(dāng)點(diǎn)E在BO上時(shí),四邊形QBED能否為直角梯形?若能,求出t的值;若不能,請(qǐng)說明理由;
(3)當(dāng)t為何值時(shí),直線DE經(jīng)過點(diǎn)O.
