A 3 kg mass is raised by 4 m. What is the gain in gravitational potential energy (g = 9.8 m/s^2)?

A 3 kg mass is raised by 4 m. What is the gain in gravitational potential energy (g = 9.8 m/s^2)?

• A. 75.6 J
• B. 117.6 J
• C. 140 J
• D. 12 J

Answer: (B)

When you lift a mass up against gravity, the gravitational potential energy increases by ΔU = m g h, where m is mass, g is the acceleration due to gravity, and h is how far you raise it. Here, m = 3 kg, g = 9.8 m/s^2, and h = 4 m. So ΔU = 3 × 9.8 × 4 = 117.6 joules. The gain in gravitational potential energy is 117.6 J. The other numbers would correspond to different heights (for example, 75.6 J would come from about 2.57 m, 140 J from about 4.76 m, and 12 J from about 0.41 m). Using the given values, 117.6 J is the correct result.

When you lift a mass up against gravity, the gravitational potential energy increases by ΔU = m g h, where m is mass, g is the acceleration due to gravity, and h is how far you raise it. Here, m = 3 kg, g = 9.8 m/s^2, and h = 4 m. So ΔU = 3 × 9.8 × 4 = 117.6 joules. The gain in gravitational potential energy is 117.6 J. The other numbers would correspond to different heights (for example, 75.6 J would come from about 2.57 m, 140 J from about 4.76 m, and 12 J from about 0.41 m). Using the given values, 117.6 J is the correct result.