如圖,在等腰梯形ABCD中,AD∥BC,AB=DC=50,AD=75,BC=135.點(diǎn)P從點(diǎn)B出發(fā)沿折線段BA-AD-DC以每秒5個(gè)單位長(zhǎng)的速度向點(diǎn)C勻速運(yùn)動(dòng);點(diǎn)Q從點(diǎn)C出發(fā)沿線段CB方向以每秒3個(gè)單位長(zhǎng)的速度勻速運(yùn)動(dòng),過點(diǎn)Q向上作射線QK⊥BC,交折線段CD-DA-AB于點(diǎn)E.點(diǎn)P、Q同時(shí)開始運(yùn)動(dòng),當(dāng)點(diǎn)P與點(diǎn)C重合時(shí)停止運(yùn)動(dòng),點(diǎn)Q也隨之停止.設(shè)點(diǎn)P、Q運(yùn)動(dòng)的時(shí)間是t秒(t>0).
(1)當(dāng)點(diǎn)P到達(dá)終點(diǎn)C時(shí),求t的值,并指出此時(shí)BQ的長(zhǎng);
(2)當(dāng)點(diǎn)P運(yùn)動(dòng)到AD上時(shí),t為何值能使PQ∥DC;
(3)設(shè)射線QK掃過梯形ABCD的面積為S,分別求出點(diǎn)E運(yùn)動(dòng)到CD、DA上時(shí),S與t的函數(shù)關(guān)系式;(不必
寫出t的取值范圍)
(4)△PQE能否成為直角三角形?若能,寫出t的取值范圍;若不能,請(qǐng)說明理由.