(1)∵A对B的压强与B对桌面的压强之比为6:7,∴ pA pB = FA压 S FB压 S = FA压 FB压 = GA GA+GB = 6 7 ,∴ GA GB = 6 1 ,∴ mA mB = 6 1 ,∵A和B边长之比是2:1,∴ VA VB = 8 1 ,∴ ρA ρB = mA VA mB VB = mA mB × VB VA = 6 1 ×