Question 1.SGPYQ.27: If, at t = 0^+ , the voltage across the coil is 120 V, the v......

i_{ L }\left(0^{-}\right)=\frac{\text { Total voltage }}{\text { Sum of resistance }}

=\frac{120}{20+40}=2  A             [Position 1]

In the inductor, the current does not change simultaneously.
Therefore,

i_{ L }\left(0^{+}\right)=i_{ L }\left(0^{-}\right)=2  A       [Position 2].

Voltage across the inductor at t=0^{+}

V_{ L }\left(0^{+}\right)=120  V

By applying KVL,

120 = 2(40 + R + 20) ⇒ R = 0 Ω