Terminal Velocity question from JEE Main 2013 (25 Apr, Shift 1)

Answer: (c)

1. At terminal speed $10$ cm/s the viscous force equals the effective weight: $F_v = W_{\text{eff}}$, with $F_v \propto v$.
2. Pulled up with $2W_{\text{eff}}$: net driving force upward $= 2W_{\text{eff}} - W_{\text{eff}} = W_{\text{eff}}$.
3. Steady speed is reached when viscous force $= W_{\text{eff}}$, i.e. at the same speed $10$ cm/s.
4. So the answer is (c) 10 cm/s.