A frustrated student drops his physics book of 2-kg out of the window that is 100 m from the ground.The kinetic energy of the book at 25 m from the ground is

Question

Quizplus · Accepted Answer

The potential energy of the book at the window is given by mgh, where m is the mass of the book (2kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height of the window (100 m). Thus, the potential energy of the book at the window is 
(2 kg) x (9.8 m/s^2) x (100 m) = 1960 J. 
When the book is 25 m from the ground, its potential energy is (2 kg) x (9.8 m/s^2) x (25m) = 490 J.
Since the total energy (potential + kinetic) of the book remains constant, we can solve for its kinetic energy at 25 m using the conservation of energy equation:
Potential energy at 25 m = Kinetic energy at 25 m
Therefore, the kinetic energy of the book at 25 m from the ground is also 490 J.

A Frustrated Student Drops His Physics Book of 2-Kg Out