Answer:
The graph C.
Explanation:
The potential energy of the book is maximum when it is on the table; therefore, the graph we are looking for must have maximum potential energy at [tex]t=0.[/tex]
Also, as the book falls down, its potential energy is decreasing; therefore, the slope of the graph must be negative.
Finally, as the book lands on the ground, its potential energy becomes zero; therefore, the graph must show potential energy of zero at some time, i.e it must contain a point [tex](t_a, 0)[/tex]
Now, looking at the four graphs given, we see that the graph C satisfies all our conditions, and therefore it is the correct choice.
For the sake of completeness, let us look at other choices.
Graph A shows potential energy non linearly increasing—not true for a falling book.
Graph B shows potential energy increasing linearly—not true for a falling book because its potential energy is decreasing.
Graph D shows that potential energy of the book does not change—cannot be true since the book is falling.
