Kinematic equation for displacement under gravity

Steps:

• Acceleration a = 9.8 m/s² downward (g).
• Initial velocity u = 20 m/s downward, time t = 1.5 s.
• Apply s = ut + (1/2)at².
• s = (20)(1.5) + (0.5)(9.8)(1.5)² = 30 + 11.025 = 41 m.

Why D is correct:

• Matches the kinematic equation s = ut + (1/2)gt² for constant acceleration due to gravity.

Why the others are wrong:

• A: Only (1/2)gt² term, ignores initial velocity.
• B: Applies ut - (1/2)gt², wrong sign for downward motion.
• C: Incorrect; possible miscalculation with g ≈ 10 m/s² and partial terms.

Final answer: D