Question

A baseball player hits a ball. Which is the best description of the energy of the ball as it flies over the pitcher’s head?

Answer 1

The ball will be subject to potential and kinetic energy at this point in time as it is still rising away from the ground and not yet subject to the pull of gravitational force. The potential energy will account for the forces occurring due to change in relative position of the ball during its flight while kinetic energy will account for the energy derived by its motion.

Answer 2

Answser: as the ball is ascending, its kinetic energy decreases and the gravitational potential energy decreases. When the ball is at the maximum altitude, the gravitational potential energy is maximum and the kinetic energy is minimum. As the ball is descending, it loses gravitational potential energy and gains kinetic energy. The total mechanical energy is conserved.

Explanation:

Remember, gravitational potential energy is due do the position (altitude) and the kinetic energy is due to motion (speed).

Mathematically they are:

Gravitational potential energy = mass × gravitaional acceleration × altitude

Kinetic energy = mass × speed² / 2.

Total mechanical energy = gravitational potential energy + kinetic energy.

The ball starts with a very low gravitational potential energy (low altitude) and high kinetic energy (high speed), as the travels upward and far away from the hitter, the kinetic energy is transferred to gravitational potential energy, so the ball gains altitude and loses speed.

When the ball reaches the maximum altitude, it has lost all the vertical speed, and the kinetic energy is at a minimum level, while its gravitational potential energy is at the maximum.

From that point, the ball starts to descend, losing grativational potential energy and gaining kinetic energy. At the moment that the ball reaches the ground it will be again at the minimum grativational potential energy and maximum kinetic energy.