在平直公路上行驶的a车和b车,其位移﹣﹣时间图象分别为图中直线a和曲线b,已知b车的加速度恒定且a=﹣2m/s2,t=3s时,直线a和曲线b刚好相切,下列说法正确的是( )
A:a车的速度大小va=2m/s
B:前3s内,a车的位移大小Sa=8m
C:b车的初速度大小vb=8m/s
D:t=0时两车相距9m
下列数据中最接近生活实际的是( )
如图所示的滑轮组提升重物,请画出最省力的绳子绕法。
A
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