What is the change in gravitational potential energy delta U_grav for a 3 kg mass raised by 4 m? (g = 9.8 m/s^2)

What is the change in gravitational potential energy delta U_grav for a 3 kg mass raised by 4 m? (g = 9.8 m/s^2)

• A. -117.6 J
• B. 0 J
• C. 117.6 J
• D. 58.8 J

Answer: (C)

Gravitational potential energy change is found from ΔUgrav = m g Δh. Raising the mass by 4 m means Δh is +4 m, so ΔUgrav = 3 kg × 9.8 m/s^2 × 4 m = 117.6 J. The positive sign reflects storing energy by lifting. A quick check: the weight is m g = 29.4 N, and lifting 4 m adds 29.4 N × 4 m = 117.6 J. The other options would imply no height change, a decrease, or only half the energy, which don’t match the given 4 m lift.

Gravitational potential energy change is found from ΔUgrav = m g Δh. Raising the mass by 4 m means Δh is +4 m, so ΔUgrav = 3 kg × 9.8 m/s^2 × 4 m = 117.6 J. The positive sign reflects storing energy by lifting. A quick check: the weight is m g = 29.4 N, and lifting 4 m adds 29.4 N × 4 m = 117.6 J. The other options would imply no height change, a decrease, or only half the energy, which don’t match the given 4 m lift.