When a ball rolls up a hill with negligible friction, which energy change is correct?

• A. Kinetic energy increases and gravitational potential energy increases
• B. Kinetic energy increases and gravitational potential energy decreases
• C. Kinetic energy decreases and gravitational potential energy increases
• D. Kinetic energy decreases and gravitational potential energy decreases

Answer: (C)

When a ball climbs a hill with negligible friction, gravity does negative work on the ball’s motion. That means energy is transferred from kinetic energy to gravitational potential energy as height increases, and no energy is lost to heat because friction is negligible. So the ball slows down, reducing its kinetic energy, while its height rises, increasing its gravitational potential energy. The result is a decrease in kinetic energy and an increase in gravitational potential energy. The other possibilities would require the ball to gain kinetic energy while climbing or to lose gravitational potential energy, which isn’t what happens under these conditions.