Force balance at terminal velocity Steps:

• Identify forces: gravitational force mg downward, electric force qE upward, air resistance kv upward (proportional to speed v).
• At terminal speed, net force is zero: mg = qE + kv.
• Rearrange for v: v = (mg - qE)/k.
• v decreases linearly with increasing E, with negative slope -q/k.

Why A is correct:

• Graph A shows v decreasing linearly with E, matching v = (mg - qE)/k from Newton's second law at equilibrium.

Why the others are wrong:

• B shows v increasing with E, contradicting electric force opposing gravity.
• C shows nonlinear decrease, but resistance is linear in v, yielding linear relation.
• D shows constant v, ignoring electric field's effect on balance.

Final answer: A