y =2+3t²
y‘ = 6t
y‘’ = 6
切向加速度与时间无关,a = y‘’ R = 6×1 = 6 m/s²
t=2时,切向速度af = (y‘)² R = (6t)² ×1 = (6*2)² × 1 = 144 m/s²
即,t=2时,质点的切向加速度 6 m/s²,法向加速度 144 m/s²