Conservation of Mechanical Energy

Steps:

• Gravity is the only force doing work, conservative, so mechanical energy (KE + PE) remains constant.
• Initial kinetic energy converts to potential energy at maximum height, then back to kinetic energy.
• No dissipative forces like air resistance, ensuring total energy invariance.
• Momentum changes due to gravitational force, violating conservation.

Why A is correct:

• Conservation of energy law states total mechanical energy E = KE + PE is constant without non-conservative forces, as ΔE = 0.

Why the others are wrong:

• B: Momentum is not conserved because external gravitational force acts on the ball, changing its velocity.
• C: Kinetic energy decreases during ascent and is zero at maximum height, so its rate of increase is zero there.
• D: Potential energy increases at a decreasing rate as velocity slows, per PE = mgh and v² = u² - 2gh.

Final answer: A