③举南演掌大 但博学求回新 South chi na Agricul tural Uni versity di di a=aia y dt dt 据上知:v=-( Rosin ot),vn=1 a=-(ro cos at )i a=rocos at 方向为x轴方向 10Dep. physics Dep. physics Dep. physics 10 2 2 ( sin ) 1 ( cos ) | | | cos | x y x y x y dv dv dv a a i a j i j dt dt dt v R t v a R t i a R t 据上知: , 方向为x轴方向