1.如圖,在Rt△ABC中,∠ABC=90°,AB=20,BC=15,AD為AC邊上的動(dòng)點(diǎn),點(diǎn)D從點(diǎn)C出發(fā),沿邊CA往A運(yùn)動(dòng),當(dāng)運(yùn)動(dòng)到點(diǎn)A時(shí)停止,設(shè)點(diǎn)D運(yùn)動(dòng)的時(shí)間為t秒,速度為每秒2個(gè)單位長(zhǎng)度.
(1)當(dāng)t為何值時(shí),△CBD是直角三角形;
(2)若△CBD是等腰三角形,求t的值.