Buoyancy-driven motion approaching terminal velocity

Steps:

• Buoyant force exceeds weight, providing initial net upward acceleration from rest.
• As upward velocity v increases, drag force rises (proportional to v or v²), reducing net force.
• Acceleration dv/dt decreases over time as drag grows.
• v approaches terminal velocity when buoyant force balances weight plus drag, making net force zero.

Why A is correct:

• Graph A depicts v rising from zero and asymptotically approaching a constant terminal velocity, consistent with Newton's second law where net force F_net = ma diminishes to zero.

Why the others are wrong:

• B shows linear v-t increase, implying constant acceleration, but drag causes deceleration in acceleration.
• C shows initial decrease then increase, contradicting upward propulsion from rest.
• D shows constant v from t=0, ignoring initial acceleration phase.

Final answer: A