15.
一質(zhì)點(diǎn)原來以8m/s的速度做勻速直線運(yùn)動(dòng),從t=0時(shí)刻開始做勻變速直線運(yùn)動(dòng),經(jīng)4s質(zhì)點(diǎn)前進(jìn)了24m.在t=4s時(shí),該質(zhì)點(diǎn)開始做勻速運(yùn)動(dòng),從t=6s開始質(zhì)點(diǎn)又做勻變速直線運(yùn)動(dòng),到t=14s時(shí)質(zhì)點(diǎn)回到t=0時(shí)刻的位置.求:
(1)前6s內(nèi)質(zhì)點(diǎn)的位移大小?
(2)質(zhì)點(diǎn)回到t=0時(shí)刻位置的速度是多大?方向如何?
(3)作出整個(gè)過程中該質(zhì)點(diǎn)運(yùn)動(dòng)的υ-t圖象.