Terminal velocity requires balanced forces over sufficient time

Steps:

• Terminal velocity occurs when gravitational force (weight) equals drag force from air resistance, resulting in zero net force and constant speed.
• Air resistance increases with the square of velocity, starting low and building as the object accelerates.
• For a heavy coin, weight is large, so high speed is needed for air resistance to match it.
• Over a short distance, acceleration time is too brief for velocity to reach the point where forces balance.

Why D is correct:

• Newton's second law shows net force = weight - air resistance; for a heavy coin over short distance, weight exceeds air resistance (F_net > 0), so acceleration continues without reaching terminal velocity.

Why the others are wrong:

• A: Hitting the ground is unrelated; failure to reach terminal velocity depends on distance fallen, not impact.
• B: A heavy coin has weight greater than initial air resistance, causing acceleration.
• C: Equal forces define terminal velocity, which the coin does not achieve.

Final answer: D