Question

a ball is dropped from the top of a building. as the ball falls, which statement best describes the energy changes taking place?
the balls kinetic energy decreases as it falls.
the balls gravitational potential energy is transformed into kinetic energy.
the balls total energy increases as it falls
the balls energy is destroyed when it hits the ground.
a roller coaster car is at the very top of the first hill and is momentarily at rest. which statement best describes the energy of the system at this point?
the car has the greatest kinetic energy and the least potential energy.
the car has the greatest potential energy and the least kinetic energy
the car has equal amounts of potential and kinetic energy
the car has no energy because it is not moving

Explanation:

For the first question: When a ball falls, its height decreases so gravitational potential energy ($mgh$) decreases, while its speed increases so kinetic energy ($\frac{1}{2}mv^2$) increases. Energy is conserved (not created or destroyed), so potential energy is converted to kinetic energy.
For the second question: At rest, the roller coaster's speed is 0, so kinetic energy ($\frac{1}{2}mv^2$) is at its minimum (0). At the top of the hill, its height is maximum, so gravitational potential energy ($mgh$) is at its greatest.

Answer:

1. The ball's gravitational potential energy is transformed into kinetic energy.
2. The car has the greatest potential energy and the least kinetic energy.