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

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

• A. 29.4 J
• B. 88.2 J
• C. 58.8 J
• D. 18.6 J

Answer: (C)

When you lift a mass in gravity, the gravitational potential energy increases by the work you do against gravity. This change is ΔU_grav = m g Δh. Plugging in m = 2 kg, g = 9.8 m/s^2, and Δh = 3 m gives ΔU_grav = 2 × 9.8 × 3 = 58.8 J. So the mass gains 58.8 joules of gravitational potential energy. If it were lowered by 3 m, the change would be −58.8 J.

When you lift a mass in gravity, the gravitational potential energy increases by the work you do against gravity. This change is ΔU_grav = m g Δh. Plugging in m = 2 kg, g = 9.8 m/s^2, and Δh = 3 m gives ΔU_grav = 2 × 9.8 × 3 = 58.8 J. So the mass gains 58.8 joules of gravitational potential energy. If it were lowered by 3 m, the change would be −58.8 J.