# Search results

1. ### A little entropy

Okay, here's my full answer. given specific heat of ice = .5 cal/g*K and specific heat water = 1 cal/g*K. Latent heat of fusion for water is 334 J/g 1 calorie = 4.184 J dQ_1 = Heat to bring ice to 0ºC = 2.092 (J/g*K) * 8600 (g) * (0--6) (K) = 107,947 J dQ_2 = Heat to melt ice. = 334...
2. ### A little entropy

Maybe a typo on my part? Whatever I put into the homework site was accepted (i think the range is +/- 1% or so). But can you explain why using the midpoint is only a rough approximation? Isn't it a linear graph when we don't consider the time involved?
3. ### A little entropy

Just thought I'd bump this quick. Just finished a test involving topics ranging from the 2nd Law of Thermodynamics and Entropy to light/electromagnetic waves to refraction/reflection and mirrors/lenses. With all those topics, fully 1/3 of the test involved an entropy problem similar to...
4. ### A little entropy

Found my error, found the right answer, but still wondering why it's clear why we can use the midpoint of dT. Specific heat of ice \neq specific heat water. Whoops. EDIT : Nevermind on that too. As long as we're not interested in the time it takes for the temperature to change, we...
5. ### A little entropy

First off, I really do appreciate the help! However, a couple questions: Is it really clear why we can use the midpoint? Sure, I get close to the right answer, but by using the midpoint we are assuming that T is changing at a constant rate, which isn't the case. While this implies the need...
6. ### A little entropy

After your first reply, that's what I was thinking. However, how/when do I determine the T for each dQ? ie, bringing the ice from -6 C to 0 C isn't a constant temperature, so how do I decide which value to use?
7. ### A little entropy

Well, the lake is transferring heat into the ice, and since the dQ1 + dQ2 = 0, the lake is contributing -3840.8 kJ. If I understand this correctly, my above answer is actually the loss of entropy of the lake itself. I then need to find the gain in entropy of the ice. (that can't be the gain...
8. ### A little entropy

Homework Statement A boater dumps 8.6 kg of ice from his cooler into the lake at the end of a fishing trip. The ice is at -6°C, and the lake is at 20.9°C. What is the change in entropy of the new lake-ice cube system after the ice cubes come to equilibrium with the lake? Homework...
9. ### Catapult Projectile Question wow

I'm going to have to write that one down. :biggrin:
10. ### Electric fields created by charged particles

The equation you need here is E = \frac{kq}{r^2} * \hat{r}, where k is the permitivity of free space. \hat{r} represents the radial unit vector from the point charge to the point where you are calculating the electric field, and shouldn't have a magnitude. (I think your * < x,y,z> is...
11. ### Kichoff Simultaneous Equations

Another thing I found helpful when I took this class is, once you follow Doc Al's advice, to set up all the equations in a matrix. It helps make the algebra easier! :smile: