{Calculation of Impedance}
\[ Z = \sqrt{(X_L - X_C)^2 + R^2} \] Given that \( X_L = X_C \), the formula simplifies to \[ Z = \sqrt{(R - R)^2 + R^2} = \sqrt{0 + R^2} = R \] Therefore, the impedance is \( R \).
A metal plate of area 10-2m2 rests on a layer of castor oil, 2 × 10-3m thick, whose viscosity coefficient is 1.55 Ns/m2. The approximate horizontal force required to move the plate with a uniform speed of 3 × 10-2ms-1 is: