Terminal velocity when net force is zero

Steps:

• Terminal velocity occurs when resultant force F = 0, so acceleration is zero.
• Set F = 0: mg - kv² = 0.
• Solve for v²: kv² = mg, so v² = mg/k.
• Take square root: v = √(mg/k).

Why A is correct:

• It directly matches the formula derived from balancing gravitational and drag forces at F = 0.

Why the others are wrong:

• B: Incorrectly places square root only on mg, ignoring the k in the denominator.
• C: Gives v = mg/k, which applies to linear drag (kv), not quadratic (kv²).
• D: Misapplies square root to k alone, yielding wrong dimensions.

Final answer: A