# Hil

Newest questions and responses by Hil
1. ## Physics

Helium balloons are used regularly in scientific research. A typical balloon would reach an altitude of 40.0 km with an air density of 4.3*10^-3 kg/m^3. At this altitude the helium in the balloon would expand to 540000.0m^3. Find the buoyant force on the

asked on December 24, 2013
2. ## physics

A closed container with a volume of 8000cm^3 is filled with Xenon gas. the temperature is 273K and the pressure is 2 atm. How many moles of Xenon are in the container? The container is now submerged in boiling water until the gas inside the container is at

asked on December 23, 2013
3. ## physics

A beam of electrons with momentum p=10^-23 kg m/s passed through a narrow slit of width d=10^-5 m. What is the uncertainty component of the momentum in the x-direction due to the uncertainty principle (approximately)? a. change in p greater or equal to

asked on December 23, 2013
4. ## Chemistry

Rank the following three elements in order of increasing Young'sModulus: Ge, Sn, Si. My answer is as follows: Sn

asked on December 20, 2013
5. ## math

Is 7.27332*10^-11 meters/second the same as 0.07 nm per second. I believe it is after rounding off. Thanks for your help.

asked on December 18, 2013
6. ## physics Classical Mechanics

a) Two pendulums consist of a very thin string at the end of which hangs a mass which is much larger than the mass of the rod. In pendulum #1, the rod is made of copper. In pendulum #2, the rod is made of invar. What is the percentage in the period of the

asked on December 14, 2013
7. ## physics Classical Mechanics

A stick of length l =70.0cm rests against the wall. The coefficient of static friction between stick and wall and between the stick and the floor are equal. The stick will slip off the wall if placed at an angle greater than theta = 41 degrees. What is the

asked on December 10, 2013
8. ## Physics Classical Mechanics

Thanks to everyone who helped me out. I got through.

asked on December 10, 2013
9. ## physicS IMP PLS

Consider a rocket in space that ejects burned fuel at a speed of Vex = 1.5 km/s with respect to the rocket. The rocket burns 5% of its mass in 280 seconds. (a) What is the speed V of the rocket after a burn time of 140 seconds (in m/s)? (b) What is the

asked on December 9, 2013
10. ## physics Classical Mechanics

Hi, Greco. I am using the following formula to solve Ballistic Missile: sqrt(5*G*m_1/4*r_1). Given the following: m_1=5*10^24kg; r_1=6000;alpha=30 degrees;r_2=(5/2)r_1; G= 6.674*10^-11kg/m^3s^-2. I thought I did it correctly using the proper formula. My

asked on December 8, 2013
11. ## Physics Classical Mechanics

MIT A uniform disc of mass m and radius r is acted upon by three forces. find the magnitude of angular acceleration and the sense of rotation. Three different cases. force F, 3F, 2F. need help, not doing so good.

asked on December 6, 2013
12. ## Physics Classical Mechanics

Greco I am having a problem with the turntable (gyroscope) problem. The angular speed is 300 radians per second. I tried a couple of formulas including one by you. Maybe I am not converting the units properly. I could use some help. I tried several

asked on November 25, 2013
13. ## Finite

For this problem, assume the balls in the box are numbered 1 through 8, and that an experiment consists of randomly selecting 3 balls one after another without replacement. What probability should be assigned to the event that at least one ball has an odd

asked on January 23, 2011
1. ## Statistics

ohh

posted on March 24, 2016
2. ## chemistry

42

posted on March 6, 2014
3. ## chemistry

No. 25 This is my answer: lowest density: cristobalite; next lowest: tridymite; next lowest: beta quartz; next lowest: alpha quartz; highest density: coesite. Please verify.

posted on December 22, 2013
4. ## chemistry

No.29 is correct. No. 18 can you check my math. ln(100)=H_v/8.314*(1/772.15-1/1109.15) ln(100)= H_v/8.314*0.000393 H_v= ln(100)*8.314/0.000393 H_v=ln(100)*21155.2163) H_v=97423.37 joules H_v=97.42337 kilo joules Thanks.

posted on December 22, 2013
5. ## chemistry

Thanks Tania. I was making calculation errors and unsure of what they were looking for on the gold problem. I am having he same problem with no 18. I know the formula but getting the wrong answer. Temp = 836 C and 499 C

posted on December 22, 2013
6. ## chemistry

On no. 25. I believe the highest density is Coesite. The others are tricky. Does anyone know. On 26, phases for Cu at 95wt.% I think is 2. At 15wt.% for Cu, I think is 2. For no. 29, I think linear structure has a larger molar volume. Branched structure a

posted on December 22, 2013
7. ## chemistry

Hi, KS and Kim. Can you help me with No. 18 electrical measurements. Metal is two orders of magnitude higher at 836 degrees than at 499 degrees C. What is the energy formation for this metal. Thanks. In(100)= H_v/8.314(1/772.15-1/1109.15)

posted on December 22, 2013
8. ## chemistry

Hi, KS and Kim. Can you help me with No. 18 electrical measurements. Metal is two orders of magnitude higher at 836 degrees than at 499 degrees C. What is the energy formation for this metal. Thanks.

posted on December 22, 2013
9. ## chemistry

Hi. KS, I have a few more to go. Only one chance left. The graphs, the one on gold, x-ray tube. If you can fill in what you have. 9b is correct.21. is b and both glasses are weaker. Thanks

posted on December 21, 2013
10. ## chemistry

9. b) I think the answer is "Both molecules are ionic but the higher melting point has a larger cohesive energy". I ruled out some of the choices, LiF has a strong lattice energy. There are a lot of choices to choose from. This is what I think.

posted on December 21, 2013
11. ## chemistry

28 is A and D

posted on December 20, 2013
12. ## chemistry

This is what I did with No. 12 Gallium Nitride. A) I said No. B) Wavelength = h*c/E_g = 6.626*10^-34 x 3*10^8/ 3.2 x 1.602 * 10^-19 = 0.388 *10^-6 This is a long shot. Maybe someone can pick up on it.

posted on December 20, 2013
13. ## chemistry

Hi KS, Thanks. 6b) 3.22*10^5

posted on December 20, 2013
14. ## chemistry

Hi, Menes. I an getting a very strange answer, which is incorrect. I must be using the wrong formula. Can you assist. Thanks.

posted on December 20, 2013
15. ## physics Classical Mechanics

a. for copper: 2.65; 1.6%; 0.014%; 0.0014% for invar: 0.00012%; 0.00072%; 0.38%; 0.58% This is what I have done so far: Change in L for copper= 17*10^-6*10^3*16= 0.272m=27.2cm Change in L for invar= 0.9*10^3*16= 0.0144m= 1.44cm b.For copper: 12 sec; 18sec;

posted on December 18, 2013
16. ## math

Steve, thanks for your help.

posted on December 18, 2013
17. ## physics Classical Mechanics

Hi, koala. I am having trouble solving for u_s. So far, tan(theta) = 2*(u_s)/(1-u_s)*(u_s+1) u_s=?

posted on December 12, 2013
18. ## Physics Classical Mechanics

Hi, Unknown. Please show formula for your answer on Venturi flow meter. I would like to compare with mine. Thanks.

posted on December 12, 2013
19. ## physicS IMP PLS

Hi, Greco. To be honest Questions 1 and the ruler are by far the most difficult for me. when I started the test I knew I was in trouble. I saw this approach: Apply the conservation of energy U= m*g*h cm Ek = m*g* (L/2)+0 l=1/3*m*L Einitial= m*g*(L/2)+0

posted on December 9, 2013
20. ## physicS IMP PLS

Hi Anonymous, I tried that problem and was unsuccessful. My answer was 8 radians. I knew it was wrong. I put that off to the side. I am just trying to get a passing grade. Thanks for your help. If I learn any thing I will let you know. Also Thanks Greco

posted on December 9, 2013
21. ## physicS IMP PLS

Hi Anonymus, So my question is V= 76.939416 m/s and a=0.2747 m/s^2 correct. Is the other information just trying to through us off? Thanks.

posted on December 9, 2013
22. ## physicS IMP PLS

I have tried to solve this problem the following way: 5% mass is burned in 280s. 1.5 km/s = 1500 m/s u=fuel speed m/s Solution: V= u*ln(1/(1-p)) 1500*ln(1/0.950) = 76.9399416 m/s a= V/t = 76.9399416/280 = 0.274785506 m/s^2 What is confusing to me what is

posted on December 9, 2013
23. ## PHYSICS IMP PLS

Hi Anon or Joe. Rocket Acceleration The following are the variables: Vex=1500m;rocket burns 5% of its mass in 280 seconds. speed v after 140 seconds? V= Vex*ln(1/(1-0.025)) V= 1500*ln(1/(1-0.025)) V= 1500*0.0253178 V=37.97612 m/s

posted on December 8, 2013
24. ## physics(URGENT!!!!!)

Can some explain Part d of doppler shift. I used the following: f'= f*(1+speed of observer/speed of sound) f'=450*(1+20/340)=450*1.0588=476.46. This is my last chance. The wind blows toward the observer. Any ideas. Thanks.

posted on December 8, 2013
25. ## physics Classical Mechanics

Hi, Greco. Thanks I got the same answer on the second try.

posted on December 8, 2013
26. ## physics Classical Mechanics

Hi, Roma. I am having the same problem as you. If I find out I will let you know. I am still trying to solve the problem on the missile.

posted on December 8, 2013
27. ## physics

I am not sure about (a) I think it is us*d(theta). (b)T/R 1/e^(us*pi)-1 (c)T/R 1/1-e^(-us*pi) I am not 100% positive. Take a look maybe you feel the same way. The tension is opposite.

posted on December 6, 2013
28. ## Physics Classical Mechanics

Thanks, Greco. I figured it out.

posted on November 27, 2013