The discussion revolves around the potential and kinetic energy of a physics book dropped from a height of 2.0 meters. Participants explore the calculations related to gravitational potential energy and kinetic energy as the book falls, while also considering the forces acting on the book during its descent.
The discussion is active, with participants providing insights into energy conservation principles and questioning the definitions of forces involved. Some guidance has been offered regarding the relationship between potential and kinetic energy, though there is no explicit consensus on the calculations presented.
Participants note potential confusion regarding units and the definitions of forces, particularly in relation to air resistance and energy conservation principles. There is an ongoing exploration of the initial and final energy states of the book.
Non-Conservative forces acting on the book are , air resistance, sound and heat. The force acting on the book are gravityvela said:What forces act on the book? Are any non-conservative?
AJKing said:How far has the book traveled?
And what are the equations that tell you velocity under constant acceleration after a certain distance?
vela said:Sound and heat aren't forces. They don't push or pull on the book, right? Air resistance, however, is a force, but you can neglect it. So gravity is the only force acting on the book, and it's conservative. So you can use energy conservation. That means the energy at the initial point is equal to the energy at the final point.
What's the total mechanical energy at the initial point? You already found the potential energy there. What is the book's kinetic energy initially? Add the two together to find the total energy.
At the final point, the book is one meter off the floor. What does the total energy consist of there?
vela said:You got the potential energy at the end almost correct. You have the wrong units.
Energy conservation says that
\begin{align*}
E_i &= E_f \\
KE_i + PE_i &= KE_f + PE_f
\end{align*} So you have the potential energies. What are the kinetic energies?
Thanks bossvela said:No. You have a formula for kinetic energy. Use that. And there are two, one at the beginning and one at the end.