# A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential

###### Question:

at the top of its trajectory. If it returns to its original level less than 100 J of kinetic energy, the ball

encountered

a. air resistance.

b. gravitational acceleration.

c. a faster descent time.

d. a decrease of its mass.

## Answers

Air resistance

Explanation:

Despite the law of conservation of energy stating that energy can neither be created nor destroyed but can only be transformed from one state to another, some energy is usually lost in the process of transformation and its majorly attributed to frictional loss. Friction opposes normal movement hence in air, air resistance tends to reduce the original energy compared to the initial. That is why the final energy in this case is slightly less than the original energy.

Option A

Air resistance

Explanation:

Despite the law of conservation of energy stating that energy can neither be created nor destroyed but can only be transformed from one state to the other, the process of transformation is not 100% efficient since some energy losses occur due to friction and air resistance. Therefore, when the final energy is slightly less than the original dor this case, it's due to energy loss due to air resistance.

To solve this problem we could apply the concepts given by the conservation of Energy.

During the launch given in terms of kinetic energy and reaching the maximum point of the object, the potential energy of the body is conserved. However, part of all this energy is lost due to the work done by the friction force due to friction with the air, therefore

[tex]E_T = PE + KE -W_f[/tex]

The potential and kinetic energy are conserved and are the same PE = KE and this value is equivalent to 100J, therefore

[tex]E_T = 100-W_f[/tex]

The kinetic energy will ultimately be less than 100J, so the correct answer is C.