Question

A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory.
When it returns to its original level after encountering air resistance, its kinetic energy is __________.

A) more than 100 J.

B) Not enough information given.

C) less than 100 J.

D) 100 J.

Answer 1

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

$E_T = PE + KE -W_f$

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

$E_T = 100-W_f$

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