如圖,在正方形ABCD中,點(diǎn)A、B的坐標(biāo)分別為(0,10),(8,4),點(diǎn)C在第一象限,動(dòng)點(diǎn)P在正方形ABCD的邊上從點(diǎn)A出發(fā)沿A→B→C以每秒一個(gè)單位長(zhǎng)度勻速運(yùn)動(dòng),同時(shí)動(dòng)點(diǎn)Q以每秒
個(gè)單位長(zhǎng)度在x正半軸上運(yùn)動(dòng),當(dāng)動(dòng)點(diǎn)P運(yùn)動(dòng)到B時(shí),Q的速度變?yōu)槊棵?個(gè)單位長(zhǎng)度勻速繼續(xù)向前運(yùn)動(dòng),當(dāng)P點(diǎn)到達(dá)C點(diǎn)時(shí)兩點(diǎn)同時(shí)停止運(yùn)動(dòng),設(shè)運(yùn)動(dòng)的時(shí)間為t秒.
(1)求正方形邊長(zhǎng)及頂點(diǎn)C的坐標(biāo);
(2)當(dāng)P點(diǎn)沿A→B上運(yùn)動(dòng)時(shí),點(diǎn)Q的橫坐標(biāo)x與運(yùn)動(dòng)時(shí)間t(秒)的函數(shù)關(guān)系式是x=
t+1,請(qǐng)寫出點(diǎn)Q運(yùn)動(dòng)起點(diǎn)的坐標(biāo);
(3)在(2)的條件下,當(dāng)P點(diǎn)沿A→B→C運(yùn)動(dòng)時(shí),是否存在適當(dāng)?shù)膖值,使△OPQ為直角三角形?若存在,求出此時(shí)t的值;若不存在,說明理由.