Question

Think about a child swinging on a swing set. She isn't pumping her legs, just swinging freely. Where is she moving fastest? Slowest? Where is her potential energy the most? The least? Where is her kinetic energy the most? The least?Now think about lifting a book to the top of a bookshelf. What is the relationship between the work done while moving a book to a higher bookshelf and the potential energy that the book has on the higher shelf? What happens to the potential energy as the book is falling to the ground. Where does the energy go when it hits the ground?Explain your answers in terms of conservation of energy.

Answer 1

when the child swinging on the set let us assume that there are no external forces acting and energy is conserved at the lowest point ,considering the lowest point as origin potential energy is zero( lowest_) and total energy is converted into kinetic energy ,so kinetic energy is most at lowest point and  she is moving fastest at the lowest point .when she is top most point of her swing maximum height above lowest point ,is reached total energy is converted into potential energy velocity becomes zero .so at the highest point of the swing her potential energy is most and speed is lowest ..

now when you are lifting the book you are doing work against gravity ,so this wok is stored as potential energy .workdone is equal to change in potential energy.As the book is falling on the ground its potential energy is converted into kinetic energy.total potential energy is converted into kinetic energy when it hits the ground this total energy is transformed into heat or used by other dissipative forces .as energy is neither destroyed nor created it is transformed from one form to another