# Search results for query: *

• Users: DH
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1. ### Academic and Research Programs in Science, Math and Engineering

Hey guys, I got Physics PhD offers from Purdue University, Stony Brook University, and Georgia Tech. Which one should I go for? Thanks
2. ### Body diagonals of a cube

Can some one tell me what are the diagonals of a cube? Picture is better
3. ### Synthesis of benzyl alcohol

start from benzaldehyde
4. ### Synthesis of benzyl alcohol

I try to find the synthesis of benzyl alcohol, but I can't get it. Can some one show me how to do the synthesis of benzyl alcohol, in detail. Can someone give me the website to find the synthesis of benzyl alcohol Thanks
5. ### Why does cold air go to the bottom of the room?

sorry, it's typing mistake I have to say like that: the lower kinetics energy can't move to the higher position while the higher kinetics move faster and so that its kinetics energy convert to potiential energy. When the molecular gas go to the higher possition, the kinetics energy convert...
6. ### Why does cold air go to the bottom of the room?

at first, from the molecular view, hot air and cold air is defined by temperture. hot air has higher temperture than cold air. The temperture presents the average kinetic energy of a molecular gas. Kinetic energy is proportional to temperture. Higher temperture has higher kinetic energy -->...
7. ### Escape velocity help

ok, to understand the concept of escape velocity, you must know about the concept of gravitational potential. The gravitational potential causes of the gravity force F = M1*M2*G/r^2 gravitional potential is the energy that require to bring a object from infinitive to the distance r from the...
8. ### Little challenge

The problem is that, after the object releases from the spring, it will accelerate.. if the velocity of object is greater than spring, the object will leave. but when?
9. ### Little challenge

An object is place against a compressed spring at the bottom of an air track that slope upward at an angle 30. When the spring is release, find at which position, the object leave the spring? Given: the spring is compressed A, the spring constant is k, m is mass of object, mass of spring is...
10. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

You made a mistake here: \int_0^1 \frac{du}{u^4+1} = \int_0^1 \frac{du}{(u^2 + \sqrt{2}u + 1)(u^2 - \sqrt{2}u + 1)} = \int_0^1 \frac{du}{2\sqrt{2}}\left(\frac{1}{u^2 - \sqrt{2}u + 1} - \frac{1}{u^2 + \sqrt{2}u + 1} \right)
11. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

but one more time, can you show me the solution! I really want to know the way you solve it to compare with my own method... Please give me the solution in detail!

13. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

Hix, you did the wrong thing form row 1 -> row 2!
14. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

show me the solution!
15. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

no no, can't do like that!
16. ### Integrating 1/(u⁴+1), 1/(u⁵+1), and 1/(u⁶+1)

Determine the integral: y = \int_{0}^{1} 1/(u^4+1)du and y = \int_{0}^{1} 1/(u^5+1)du and y = \int_{0}^{1} 1/(u^6+1)du
17. ### When they combine

hix, When Cl- and Na+ combine, they don't release Energy! - When NaCl disolves in water, it releases Energy! When Na + Cl2 -> NaCl it release energy!
18. ### How do I prove this?

ok, but i think that i got another way set y = \lim _{n \to \infty} (3n)^{\frac{1}{2n}} we take = lny = ln( \lim _{n \to \infty} (3n)^{\frac{1}{2n}}) Since ln( \lim _{n \to \infty} (3n)^{\frac{1}{2n}}) is continuous function --> lny = \lim _{n \to \infty}[ln (3n)^{\frac{1}{2n}}] lny =...
19. ### Enthelpy of formation

ok, here is your answer. this one is the easy one! time first and third one with 2, then add three of them up, we have: 4 NO + 2O2 + 4NO2 + O2 + 2N2 + 2O2 -> 4NO2 +2N2O5 + 4NO 5O2 + 2N2 -> 2N2O5 ∆H° = 2*(-114.1) -110.2 + 2*180.5 = 22.6 -> standard enthalpy of formation of N2O5 = 22.6/2 =...
20. ### Heat of Vaporization

this is very easy problem! Heat of vaporization of Titanium 4 cloride: heat required to vaporized Tian... --> from liquid to gas ------------- Solve: you reverse the first equation: TiCl4 (l) --->Ti (s) + 2Cl2 (g) Standard Molar Enthalpy of formation= +804.2 KJ/mole Then you combine with...
21. ### How to prove x^2 = xsinx + cosx

Ok, here is the solution At first you take the derivative: y = x^2 - xsinx - cosx -> y' = 2x - xcosx We set y'= 0 to find the critical number y' = 0 when x(2-cosx) = 0 Since: -1< cosx< 1 -> 2-cosx > 0 with all x -> y' = 0 when x = 0 , and x = 0 is the only one critical number. At x = 0...