Most popular questions and responses by Lena
  1. Physics

    The range of human hearing extends from approximately 20 Hz to 20000 Hz. Find the wavelength of these extremes when the speed of sound in air is equal to 343 m/s.

    asked on April 11, 2010
  2. Physics

    How is Snell's law being used in real life application?

    asked on February 9, 2009
  3. Calculus

    Oil is leaking out of a ruptured tanker at a rate of r = 19e^(2t) gallons per hour. Write a definite integral that represents the total quantity of oil which leaks out of the tanker in the first 3 hours. Using your formula answer the following questions:

    asked on November 14, 2010
  4. chemistry

    Methane (CH4) burns in oxygen to produce carbon dioxide and water vapor. The balanced equation is: CH4 + 2 O2 -> CO2 + 2 H2O What volume of carbon dioxide is produced when 3.2 L of oxygen are consumed?

    asked on December 5, 2012
  5. Friction

    A 200kg crate us pushed horizontally with a force of 700 N. If the coefficient of friction is 0.20, calculate the acceleratio of the crate. I tried doing this but I don't seem to be getting the right answer. m = 200 kg f(app)= 700 N U = 0.20 Ff =

    asked on April 17, 2009
  6. chemistry

    Methane (CH4) burns in oxygen to produce carbon dioxide and water vapor. The balanced equation is: CH4 + 2 O2 -> CO2 + 2 H2O What volume of carbon dioxide is produced when 3.2 L of oxygen are consumed?

    asked on December 5, 2012
  7. physics

    a 1.2 kg cart slides eastward down a frictionless ramp from a height of 1.8 m and then onto a horizontal surface where it has a head-on elastic collision with a stationary 2.0 kg cart cushioned by an ideal Hooke's law spring. the maximum compression of the

    asked on November 18, 2013
  8. chem

    Calculate the pH of 0.20 M NaCN solution. NaCN ---> Na+ + CN- CN- + H20+ ---> HCN+ + OH- Initial conc. of CN- = 0.20 mol/L change = -x equillibrium = 0.20-x HCN equill. = +x OH equill. = 1x10^-7+x Ka= 6.2 x 10^-10 Kb = KW/Ka = 1x10^-14/6n2 x 10^-10 = 1.6 x

    asked on July 24, 2009
  9. chemistry

    A studen is asket to calculate the amount of heat involved in changing 10.0 g of liquid bomine at room temperature (22.5 C) to vapor at 59.0 C. To do this, one must know specific heat (0.474 J/g*C), boiling point (59 C), and heat of vaporization (29.6

    asked on March 30, 2011
  10. Chemistry

    what volume of concentrated 18M H2SO4 is required to prepare 250mL of a 6.0M solution? how would you solve this problem? i know it has something to do with the molarity formula but no idea how to apply it

    asked on March 4, 2014
  11. MATH


    asked on September 30, 2014
  12. Physics

    You are driving 2500 Kg car at a constant speed of 14 m/s along an icy, but stright and lvel road. While approaching a traffic light, it turns red. You slam on the brakes. You wheels lock, the tires begin skidding and the car slides to a halt in a distance

    asked on April 17, 2009
  13. SCI

    so would it be better to place a wilted flower in tap water or distilled water? Answer: I would say distilled water because it contains a lower cocnentration of solute than the flower and therefore the water would more easily diffuse into the flower. Tap

    asked on September 23, 2008
  14. Chemistry

    In an experiment, you dissolve 0.30 g of KHP (MM = 204.22 g/mol) in 20 mL of DI water and titrate the sample with 0.10 M NaOH. Calculate the volume (to the nearest mL) of NaOH required to reach the equivalence point. IS it a) 3 b)15 c)20 d)30 e)100 I have

    asked on January 8, 2015
  15. Chem help

    Answer the questions below for an element that has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s1. A. What is the symbol for this element? B. What is the atomic number of this element? C. How many unpaired electrons does an atom of this elelemt have?

    asked on October 17, 2012
  16. Physics

    We were doing a refraction lab where you passed a lazer beam through a water in a semi-circular dish. I was wondering why we used a semi-circular shape?

    asked on February 8, 2009
  17. world history

    1. How does the story of Coca-Cola relate to the rise of capitalism and entrepreneurship in the 19th and early 20th c? 2. what is the "iron curtain"?

    asked on August 29, 2013
  18. Chemistry

    I did a lab where I put Copper (II) Chloride in water with Alumnim. 2Al + 3CuCl2 -> 3Cu + 2AlCl3 The aluminum on the reactant side weighs 0.5 g and the CuClw weighs 1.69 grams. It said to find the theoricital yield. Did I do this right? 2Al + 3CuCl2 -> 3Cu

    asked on November 5, 2008
  19. Science

    When we look at a leaf, we see the colors of light that are reflected off its surface. How does this explain there relatively low flow of oxygen in green light?

    asked on September 24, 2009
  20. math

    Scientists are conducting an experiment with a gas in a sealed container. The mass of the gas is measured, and the scientists realize that the gas is leaking over time in a linear way. Six minutes since the experiment started, the gas had a mass of 144

    asked on February 3, 2016
  21. Chemistry

    in the presence of NH3, Cu+2 forms the complex ion [Cu(NH3)4]+2. If the equilibrium concentrations of Cu+2 and [Cu(NH3)4]+2 are 1.8x10^-17M and 1.0x10^-3M respectively, in a 1.5 M NH3 solution, calculate the value for the overall formation constant of

    asked on April 3, 2012
  22. CHEM

    A concentrated weak acid is best described as which of the following? (a) a solution with a high pH (b) a solution where the concentration of undissociated acid particles is high and relative quantity of hydronium ions is low (c) a solution where the

    asked on July 24, 2009
  23. CHEM HELP!!!

    The solubility of AgCl(s) in water at 25 C is 1.33x10^-5 M and its deltaH of solution is 65.7 kJ/mol . What is its solubility at 60.1 C ? Please explain how to solve for this!!

    asked on March 22, 2013
  24. Math/Radioactive Dating

    My teacher said that if the ratio of mass (in a rock) for 40K and 40Ar was 1:3 then the age of the rock would be 2.5 billion years. I don't understand how he concluded that to be the age. The only thing he knew was that the half-life of K40 = 1.25 billion

    asked on February 19, 2011
  25. Math

    Compare partial products and regrouping. Describe how the methods are alike and different. ♡♡♡♡?????????

    asked on October 27, 2016
  26. Conversions!

    1. The price of gold is 200 dollars/oz. How much did 1 g of gold cost that day? (1 oz = 28.4 g)Use dimensional analysis. 2. How many minutes does it take light from the sun to reach Earth? (Distance from sun to Earth is 93 million mi, speed of light= 3 x

    asked on August 25, 2007
  27. Chem

    I had a question that said would butane sink to the floor or rise to the ceiling in air. I would say sink to the floor but I was googling this and several sites said it wouldn't completely sink and that it would float. Is this right? And if so how would I

    asked on December 12, 2008
  28. Physics

    In a demonstration in physics class, a 1.2 kg dynamics cart starts from rest at the top of a ramp. the ramp is 2.4 m above the ground. the cart then rolls down to the bottom of the ramp, where it collides with a stationary 1.4 kg dynamics cart. Assume that

    asked on November 18, 2013
  29. Chem

    I don't understand the effect of temperature on a reaction. For exmaple: CO + 3H2 CH4 + H2O deltaH= -230 KJ If there were an increase in temperature then the CH4 and H2O would have a harding time becoming the CO and H2 so therefore the reaction would move

    asked on July 19, 2009
  30. chem

    how would I do the elimination reaction of 2-chloropentane. When I figured it out I got the products as being 1-pentene and hydrogen chloride. Is this correct?

    asked on March 13, 2009
  31. bob -sci.

    keeping osmosis in mind, would it be better to soak wilted flowers in distilled water or normal tap water? I was thinking tap but I`m not sure why I`m thinking that. Maybe because tap water has a higher solute concentration that than distilled. i`m not

    asked on September 23, 2008
  32. Madison

    Elliot put 7 cups of tea into the pitcher shown. How many more cups of tea does he need to fill the pitcher? (1 quart = 4 cups)

    asked on March 26, 2015
  33. Shakespeare

    How would I use ellipses in Shakspearean quotes? I know that after every line you put a / but I want to omit like half a speech and get to the end. How would I do this? This is what I want to use: “You call me misbeliever, cutthroat dog/ And you spit

    asked on May 6, 2009
  34. Physic

    You are moving into an apartment and take the elevator to the 6th floor. Suppose your weight is 640 N and that of your belongings is 940 N. (a) Determine the work done by the elevator in lifting you and your belongings up to the 6th floor (15.2 m) at a

    asked on March 5, 2015
  35. Chemistry

    Calculate the pOH of a 15 mL sample of 0.76 mol/L hydrosulfuric acid given that it only dissosiates 92% in solution.

    asked on May 27, 2019
  36. Chemistry

    Initially, 1.68 mol of PCl5(g) and 0.36 mol of PCl3(g) are in mixed in a 2.00 l container. It is later found that 1.44 mol of PCl5 are present when the system has reached equillibrium. Calculate the value of the equllibrium. This is what I did: Equation:

    asked on July 19, 2009
  37. Chem

    One of my questions asks, when can you conclude about the relative equillibrium concentrations of CrO4^2- in each of the colutions 0.1 M K2Cr2O7 and 0.1 M K2CrO4? Im really confused by this question. Could someone clarify it for me? Thanks :)

    asked on July 21, 2009
  38. Chem

    What 4 quantum numbers describes one of the outermost electrons in a strontium atom in ground state? 5,0,0,1/2 Is my answer correct?

    asked on July 7, 2009
  39. Physics

    As a traffic light turns green, a waiting car starts with a constant acceleration of 6.0 m/s^2.At the instant the car begins to accelerate, a truck with a constant velcoity of 21 m/s pass in the next lane. (a) How far will the car travel before it

    asked on April 17, 2009
  40. Biochemistry

    The Go’ value for the hydrolysis of glucose-6-phosphate is -13.8 kJ/mol. Assuming a concentration of 4 mM for this molecule, what would the phosphate concentration be at equilibrium (G = 0). Remember to convert kJ to J.

    asked on February 11, 2013
  41. The Excavation : By Augusto Roa Bastos

    I read this short story and I understand it pretty much but there are some things Im confused about. Were all the people in Cell 5 murdered by machine gun fire? Did Perucho Rodi escape from Cell 4 and avoid getting caught as one of the people involved? Was

    asked on September 26, 2009
  42. physical

    1.What kind of information is indicated by the graph of the acceleration due to gravity versus ball¡¯s mass if the slope of the curve is zero?

    asked on March 16, 2015
  43. CHEM

    Silicon carbide, commonly known as carborundum, is a very hard and abrasive substance. The compound is prepared by heating silicon dioxide in the presence of graphitic carbon: SiO2(s) + 2C(s) --> SiC(s) + CO2(g) How many grams of silicon carbide can be

    asked on October 18, 2012
  44. CHEM

    I don't understand how to find the formula of a hydrate. Here's one of the question. if you guide me through it I think I'll be able to do the rest of them. Thanks :) When 100g of ZnSO4xœH2O is heated, 43.86g of water is given off. Calculate the formula

    asked on January 22, 2009
  45. Chemistry

    Why does the temperature in exothermic reactions increase, reach a maximum, and then decrease?

    asked on October 19, 2015
  46. Math

    Beginning at age 35, Ms. Trinh invests $4000 each year into an IRA account until she retires. When she retires she plans to withdraw equal amounts each year that will deplete the account when she is 80. Find the annual amounts she will receive for each of

    asked on March 13, 2015
  47. Chemistry

    A student did the Synthesis of Salicylic Acid experiment starting with 3.89 g of methyl salicylate (C8H8O3) and using 40 mL of 6.0 M NaOH. To evaluate her success she needs to determine the limiting reagent. The reaction goes as follows: C8H8O3 + H2O ==>

    asked on November 16, 2010
  48. Math

    Conner estimated that the radius of one of the circles on the playground was 2 yards. If Conner was correct then: a. the radius was how many feet? b. the diameter was how many feet? Thanks!

    asked on November 5, 2009
  49. Physics

    A blue car moving at constant speed of 10m/s passes a polic car that is at rest. The police car accelerates from rest at 4m/s^2 for 3.0 seconds and then maintains a constant speed. The blue car maintains constant speed for the entire 12 seconds. When does

    asked on April 17, 2009
  50. CHEM

    Arrange the following in order of increasing atomic radii from smallest to largest. Mg Ra Sr Be Ca Ba

    asked on October 18, 2012
  51. History

    What are some adjectives that could be used to describe the survivors of the Holocaust? - brave have any more?

    asked on May 12, 2008

    What element is represented by this electron ground state configuration : [Kr] 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 6d2 7s2 Is this really Krypton?

    asked on October 18, 2012
  53. Chemistry

    I did a ester lab not too long ago I was wondering why we submerged the ester in cold water before we started to waft the smell towards us.

    asked on March 25, 2009
  54. English; grammar

    Could you please tell me if I have properly identified the part of speech of each word. If I have made a mistake, could you please correct me. - Word: femurs Sentance:Jawbones, hipbones, femurs. Part of Speech:NOUN Word: Apache Sentance: White smoke puffed

    asked on May 11, 2008
  55. Physics

    The inner and outer surfaces of a cell membrane carry a negative and positive charge, respectively. Because of these charges, a potential difference of about 0.070 V exists across the membrane. The thickness of the membrane is 0.000000008 m. What is the

    asked on April 19, 2014
  56. chem

    methyl benzene + oxygen is this just a combustion reactions so CO2 and H2O are produced?

    asked on March 12, 2009
  57. Chem

    What are some pros and cons for energy level diagrams and electron configuration diagrams? I was very long for elements like uranium and such but im not sure if those are the types of answers im supposed to be giving. Are there any flaws in the two methods

    asked on July 7, 2009
  58. Science

    Which of the following is a way to improve the efficiency of a heat engine? increase Qh reduce Qh reduce Wnet increase Qc A What are the energies associated with atomic motion called? kinetic energy potential energy bond energy internal energy D A 0.10 kg

    asked on January 23, 2012
  59. Maths

    Give three different ways of partitioning 775 answer

    asked on October 6, 2019
  60. Chem

    The question is telling me that NaOH (24.00 grams) is diluted in water (750 mL). Find the pH and pOH. This is what I did so far: NaOH ---> Na+ + OH- NaOH: mass = 24.00 grams v= 750 ml = 0.750 L M= 40.00 grams/mol n= 0.6000 mol c= 0.800 mol/L Since NaOH

    asked on July 27, 2009
  61. Chemistry

    what is the pH and pOH of a solution made by adding water to 15 grams of HCl until the volume of the solution is 2500mL?

    asked on April 5, 2014
  62. Calculus

    The area a meadow was approximated by measuring the length of the meadow at 30-foot intervals. THe distances measured across the meadow were 76 ft, 118 ft, 130 ft, 143 ft, 139 ft, 136 ft, 137 ft, 139 ft, 130 ft, 122 ft, and 60 ft. Use Simpson's Rule to

    asked on February 26, 2011
  63. Chemistry

    How many milliliters of 0.710 M HCl are required to react with 47.80 grams of CaCO3 ? Given the balanced reaction equation: 6 FeCl2(aq) + K2Cr2O7(aq) + 14 HCl(aq) 6 FeCl3(aq) + 2 CrCl3(aq) + 2 KCl(aq) + 7 H2O(l) How many moles of FeCl2(aq) are required to

    asked on November 28, 2010
  64. Chem

    Is a C-H bond polar or non-polar? Is a C-Cl bond polar or non-polar? I have different sources giving me different ranges. One says that anything with an electronegetivity of 0.5 or less is non-polar and I have anothre source saying anything 0.3 and less is

    asked on July 8, 2009
  65. Chem

    volume = 322 mL temperature = 150 celcius pressure = 175 kPa mass = 0.448 Calculate the molar mass of the gas. First I converted volume to 0.332 L. Second I converted 150 celcius into 423 kelvin. PV = nRt (175)(0.322) = n(8.314)(423) n= 0.016022988 molar

    asked on July 6, 2009
  66. Physic

    A person pulls a toboggan for a distance of 43.1 m along the snow with a rope directed 33.3 ° above the snow. The tension in the rope is 109 N. (a) How much work is done on the toboggan by the tension force? (b) How much work is done if the same tension

    asked on March 5, 2015
  67. Hydrogen bonding with polypeptides

    In a polypeptide at physiologic pH, hydrogen bonding may form between which of the following? a) side chains of leucine residue and lysine residue b) side chains of aspartyl residue and glutamyl residue c) terminal amino acid group and terminal carboxyl

    asked on March 3, 2011
  68. Calculus

    q 0 125 250 375 500 625 750 C'(q) 26 24 30 26 23 25 29 a) If the fixed cost is $8500, use the average of left- and right-hand sums to determine the total cost of producing 500 units. Answer: $ b) How much would the total cost increase if production were

    asked on November 15, 2010
  69. Biology

    The type of cartilage associated with bone function and development is what? I know that the elastic cartilage contains elastin which allows for elasticity and maintains shape of certain structures. Fibro is strong and rigid (strongest of 3) Hyaline

    asked on September 26, 2010
  70. Math-please help!

    the area of the base of a triangular prisim A is 15 square inches and its altitude is 8 inches. Rectangular prism B has a square base that measures 2 inches on each side. If prisim A and prisim B have the same volumes, what must be the altitude of prisim

    asked on April 12, 2010
  71. Careers

    How has the job of a sous chef changed over time? I'm not too sure about this. Sous chef has always worked for the head chef and has always done what the head chef has told him/her to do.

    asked on February 21, 2010

    Whats the difference between the formulas for kinetic and static friction. Kinetic: Ff= ukFn Static: Ff= usFn Are the 'f' and the 'n' the mass of the object? Are the 'k' and the 's' just the

    asked on April 16, 2009
  73. math/chem

    I need to find the mass of butane gas and I only know the following things (you cannot use the molar mass of butane): volume = 80 mL pressure = 98.23 KPa temp.= 298K So I found the number of mols and I got 0.003171814 mols. of butane. But I don't know what

    asked on December 12, 2008
  74. Math

    When completing the square: 5x^2 + 10x - 20 5 ( x^2 + 2x) -20 = 0 5 ( x + 1)^2 -15 = 0 Did I do that right? If so I have another question. When it's in this form, -15 is the y-coordinate of the vertex and 2 the x coordinate of the vertex? If so isnt the x

    asked on January 23, 2008
  75. Physics

    Your vertical spring accelerometer has a 200 g mass hanging from it. You climb aboard the roller coaster and watch the accelerometer read 0.4 g for 3 seconds while descending the first peak and then change to 1.5 g for 2 seconds while climbing the second

    asked on May 28, 2018
  76. Determination of ASA Content of Tablets Lab Report

    Not asking for answers necesarily but I would to know how to approach each question Mass of pure acetylsalicylic acid (ASA) : .508 g Dilution Absorbance (a.u.) 2:11 .116 4:11 .259 6:11 .392 8:11 .502 10:11 .548 Mass of tablet : .380 g Absorbance read on

    asked on December 5, 2012
  77. Bio

    The type of cartilage associated with bone function and development is what? I know that the elastic cartilage contains elastin which allows for elasticity and maintains shape of certain structures. Fibro is strong and rigid (strongest of 3) Hyaline

    asked on September 26, 2010
  78. physics

    how does a magnify glass create a virtual image?

    asked on September 21, 2009
  79. Chem

    How many moles of hydrogen and oxygen are in 2 moles of water? water: h2o # of molecules = (6.022 x 10^23)(2)= 1.2044 x 10^23 # of hydrogen atoms = (1.2044 x 10^23)(2)= 2.4088 x 10^24 # of oxygen atoms = 1.2044 x 10^24 Did I do this correctly? What do I do

    asked on July 6, 2009
  80. Chem, could someone cheak my work please.

    I did this experiment where I filled a graduated cylinder with water. The I put a stopper on it and put it under water and removed the stopper. The with a modified lighter (that wouldn't release sparks) I added butane gas. I got the following results: mass

    asked on December 12, 2008
  81. Physics

    A horizontal spring with spring constant 110N/m is compressed 16cm and used to launch a 2.8kg box across a frictionless, horizontal surface. After the box travels some distance, the surface becomes rough. The coefficient of kinetic friction of the box on

    asked on June 8, 2014
  82. Math

    I don't think I am understanding this question. Question: A zoo started with 16 cranes and panned to hatch 20 chicks. A few birds were kept for breeding and the rest realeased into the wild. At the end of last year, a total of 136 cranes had spent some

    asked on June 7, 2009
  83. world history

    how did the cold war influence events in the postwar period I can't find this in my textbook. could someone explain please

    asked on March 15, 2018
  84. Physic

    A 16-kg sled is being pulled along the horizontal snow-covered ground by a horizontal force of 27 N. Starting from rest, the sled attains a speed of 2.2 m/s in 9.6 m. Find the coefficient of kinetic friction between the runners of the sled and the snow.

    asked on March 5, 2015
  85. Physics

    A 4.5kg box slides down a 4.1-m -high frictionless hill, starting from rest, across a 1.7-m -wide horizontal surface, then hits a horizontal spring with spring constant 490N/m . The other end of the spring is anchored against a wall. The ground under the

    asked on June 8, 2014
  86. world history

    How has the global economy changed after the Cold War?

    asked on April 19, 2014
  87. stat

    if the heights of men follow a normal distribution, and 99.7% fall between 5" and 7" what is the estimate standard deviation of the height?

    asked on February 2, 2013
  88. Chemistry please help

    State Dalton’s Postulates? In light of modern knowledge, what are the inaccuracies in Dalton’s Postulates? I know Dalton's postulates: -All matter consists of tiny, indivisible particles called atoms that cannot be created or destroyed -Atoms of one

    asked on February 19, 2012
  89. science

    "Two children who are fighting over a toy pull on it from opposite sides. The result is a stand-off. Explain this in terms of the net force."

    asked on March 11, 2010
  90. english

    It is quite alone, standing well back from the road, quite three miles from the village… It makes me think of English places that you read about, for there are hedges and walls and gates that lock…For the windows are barred for little children and

    asked on September 23, 2009
  91. English

    If you hang back and reserve and criticise at first, you are preventing yourself from getting the fullest possible value from what you read. But if you open your mind as widely as possible, then signs and hints of almost imperceptible fineness, from the

    asked on September 11, 2009
  92. Chem

    Methylaime, CH3NH2. If a 0.100 mol/L solution of methyamine has a pH of 11.80, calculate the ionization constant for the weak base. What is an ionization constant. Is it just K? This is what I did so far: 11.80 = -log (concentration of h3o+) 10^-11.80 =

    asked on July 23, 2009
  93. Chem

    If I were to use dichromate and add HCL and Ba(NO3)2 and NaOH , what should form? Im thinking the Ba(NO3)2 would still form a precipitate but im not too sure about everything else

    asked on July 22, 2009
  94. Physic

    The concepts in this problem are similar to those in Multiple-Concept Example 4, except that the force doing the work in this problem is the tension in the cable. A rescue helicopter lifts a 75.4-kg person straight up by means of a cable. The person has an

    asked on March 5, 2015
  95. Chem

    Balance the following chemical equation (put the coefficients in order) Fe + O2 + H2O → Fe(OH)

    asked on October 10, 2012
  96. Biochem - Diabetes

    Type 1 diabetic injected insufficient insulin so her body can’t use glucose in blood. Blood glucose is 38 mM (normal value = 3.3-5.8 mM). To adjust osmolality, she increased urine output = dehydration. Should she be treated with water? The answer is NO

    asked on February 27, 2011
  97. calculus ap

    what is the slope of a line tangent to y=sin^2(5x+pi) at x=pi/4?

    asked on January 2, 2011
  98. Chemistry

    student did the Synthesis of Salicylic Acid experiment using 3.93 g of methyl salicylate. This was the limiting reagent for his experiment. What is the theoretical yield of salicylic acid for his experiment? The theoretical yield is:

    asked on November 16, 2010
  99. ECE 201

    Why is it important for teachers to understand students’ culture and backgrounds in an effort to address challenging behavior?

    asked on September 25, 2014
  100. ap world history

    how did wheat impact the Americas?

    asked on September 22, 2013


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