# Search results

1. ### Is the Carnot efficiency valid for fuel cells?

So, I've read in books and on Wikipedia (see for instance http://en.wikipedia.org/wiki/Carnot%27s_theorem_%28thermodynamics%29#Applicability_to_fuel_cells_and_batteries) that the Carnot efficiency cannot be applied to a fuel cell because it is not a heat engine that produces work, operating...
2. ### Heat exchanged between two gases

Homework Statement A horizontal container with adiabatic walls has a vertical wall inside it which divides the container in two. The wall is free to move back and forth and is not adiabatic. Initially, 1 kg of air is in the compartment to the left of the wall, at 5 bar and 350 K, and to the...
3. ### Incorrect solution to impulsive dynamics problem?

Hey, all! Browsing around the library for some mechanics books, I happened to come across Manuel Prieto Alberca's Curso de Mecánica Racional. Dinámica. In this book, I managed to find an interesting problem that is also solved, but having talked to other people, I have started to suspect that...
4. ### Entropy of water-ice bath

Hey, all. I'm tutoring a freshman, and we've come to this particular problem, and I think there's missing data. He does have access to the vapor tables, but as you can see, he's not given total mass, volume, nor any specific heat... here goes: "An adiabatic calorimeter contains a water-ice...
5. ### Examples where rot F = 0 don't imply conservative field

Hey, all. Anyway, I've been looking at books and sources online, and the only counterexample to the wrongly stated theorem \nabla \times \mathbf{F} = 0 \Leftrightarrow \text{conservative vector field} seems to be \mathbf{F} = \left(\frac{-y}{x^2+y^2}, \frac{x}{x^2+y^2} \right), or other...
6. ### Strange indefinite integral

Hey, all. Anyway, browsing the Internet a bit I found this integral: \int \sqrt{1 + \frac{\ln x}{x}}dx as a proposed problem in a compilation of maths problems, as an integral from the MATYC journal. I gave it to Mathematica and WolframAlpha and they weren't able to solve it...
7. ### Experiment where Second Law is violated

Hi, all. A while ago, I was told of an experiment where the Second Law of Thermodynamics was violated. The experiment involved mirrors or some other sort of optical devices to "move around" some particles, and upon moving these around, the entropy of the universe decreases. I was wondering...
8. ### Paralle plate capacitor, LIH dielectric, fringing field

Hey, all. If we partially introduce a linear, isotropic and homogeneous dielectric slab in a charged, isolated, parallel plate capacitor, we know that it experiences a forces pulling it into the dielectric, and we can obtain the expression of this force using energy considerations. However...
9. ### Continuum mechanics book, physics approach

Hey, all. What would be some good books on continuum mechanics for undergraduates majoring in Physics? I'm familiar with Timoshenko's book that's used in Engineering, but I'm looking for something a Physics student may use. Thanks in advance.
10. ### Work required to extract fluid

Homework Statement A right circular cone with water has a height of 6 ft and the upper circular base has a radius of 8 ft. How much work is needed to empty said container if the extraction is done from above? Homework Equations The Attempt at a Solution First of all, I tried...
11. ### Bar in static equilibrium + hydrostatics

Homework Statement A thin metal bar of length L is attached to a pivot point (point A in diagram). The bar is partially submerged in water and it can move freely around an axis that forms a 90 degree angle with the plane of the diagram. The density of the bar is 0.4 g cm^(-3). What...