【例】 60 0000 x=(210t)m+280m +t(s) 0123456 20 15 d (420)m/s 050 t(s 123456 642 a=4.20ms dy 2 a==420m/s dt I(S) 0 12345616 【例】 2 4.20m s d d = = t v a (4.20 )m s d d t t x v = = (2.10 )m 2.80m 2 x = t +