Make a rough sketch showing how the following properties of a baseball depend on

Question

Make a rough sketch showing how the following

properties of a baseball depend on time,

from the moment it is hit high into left field to

the time it is caught by the outfielder. You may

neglect the effects of friction in parts (a)–(c).

(a) Kinetic energy (K)

(b) Potential energy (V)

(c) Total energy (E)

(d) How would friction change the above

results? Answer this question in the form of

a typed (not handwritten) paragraph composed

of complete sentences, which could

be understood by an average baseball fan.

Explanation / Answer

When the ball is just hit, the ball possesses maximum kinetic energy. As it goes high above the ground, it starts to decelerate because of downwards acceleration due to gravity. As a result, its kinetic energy decreases while its potential energy rises. This happens until the ball reaches a maximum height. This is where the kinetic energy will be zero (ball is momentarily at rest) and the potential energy is maximum. The total energy of the ball is constant throughout and is equal to the sum of kinetic and potential energy at any given time. As the ball now comes downwards, it starts to accelerate due to gravitational acceleration. This increases its kinetic energy as it comes down while decreasing the potential energy until the ball is caught by the outfielder on the ground (hence zero potential energy).

If friction is introduced, the situation becomes a bit different. The ball initially gains kinetic energy as a result of being hit by a player but as it travels upwards, it faces a frictional force (air resistance, for example) and thus at its highest point, the potential energy is less than the maximum kinetic energy which it had just after being hit. While coming down, the ball again faces the frictional force and so when the ball is caught by the outfielder, the kinetic energy of the ball is much lower than the initial kinetic energy it had just after being hit. This happens because the total energy of the ball was not constant and it kept decreasing due to the frictional force.

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