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m = 1kg,F1 = 4N
做匀速运动时摩擦力=拉力:f = F1 = 4N
F2 = 6N时:
F2-f=ma1
加速度a1 = (F2-f)/m = (6-4)/1 = 2m/s^2
匀速运动位移:X1=v0t1 = 2*4 = 8m
撤去外力前速度v=v0+at2=2+2*2 = 6m/s
加速过程位移:X2=(v^2-v0^2)/(2a1) = (6^2-2^2)/(2*2) = 32/4 = 8m
撤去外力后减速度a2 = f/m = 4/1 = 4m/s^2
减速阶段位移:X3=v^2/(2a2) = 6^2/(2*4) = 4.5m
总位移:X=X1+X2+X3=8+8+4.5 = 20.5m
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