Friday

August 28, 2015
Total # Posts: 11,307

**(2-8) Chemistry - Science (Dr. Bob222)**

For B, think of the ideal gas as a compressed spring. When the compressed spring expands, it does work on the surroundings. The external pressure has to stay constant to ensure work is done. If the external pressure decreases, the system can expand without doing any work.
*May 11, 2014*

**ALGEBRA**

I suspect the equation should read P = 14.7e-0.21a in order that the pressure decreases with altitude. For P=13.29 13.29=14.70.21a e0.21a = 13.29/14.7 take log on both sides -0.21a = ln(13.29/14.7) a=-ln(13.29/14.7)/0.21 = 0.4802 miles = 2535.3 feet (approx.) = 2535 feet (...
*May 11, 2014*

**Physics**

m1u1+m2u2=m1v1+m2v2 12*15+36*5=12*6+36*v2 Solve for v2.
*May 11, 2014*

**math**

effective rate =(1+i/n)^n - 1 where n is the number of compounding per year. For 7% compounded semi-annually, n=2, and i=0.07 effective rate =(1+0.07/2)²-1 = 7.1225%
*May 11, 2014*

**Chemistry help**

Think of some of the energy released has been used to transform water(l) to water(g) and adjust accordingly. Watch the stoichiometric coefficient of H2O.
*May 11, 2014*

**Calc**

Oops, I got the function wrong, got an extra t on the right hand side. Go with Steve's solution.
*May 11, 2014*

**Calc**

dy/dt=-0.15y dy/y = -0.15t ln(y)=-(0.15/2)t²+C f(t)=y=Ce-0.075t^sup2; At t=0, y=3 ml. f(0)=C=3 so, let t=time for second dose, f(t)=3e-0.075t^sup2; solve for f(t)=1 ml. -0.075t²=ln(1/3) t=sqrt(-ln(1/3)/-0.075) =3.8273 (approx.) Time for third dose (after second dose...
*May 11, 2014*

**chemistry**

Convert 811 cg to kilograms 811.0 cg = 811.0/100 g = 8.110/1000 kg =0.008110 kg Then use formula to calculate concentration in ppm. Keep the answer to 4 significant figures.
*May 11, 2014*

**chemistry, first year university**

Assuming the temperature was at STP (0°C). Consider a 1-L volume. Total pressure = 421959.129Pa = 421.96 kPa = 4.1654 atm at 0°C Partial pressure of each product = 2.08272 atm This implies PN2=PH2 =2.08272 atm Kp=PN2²PH2² = 2.0827^4 = 18.8158475075608 = 1.882...
*May 11, 2014*

**chemistry**

oops! The example reaction should read: HCl + H2O -> H3O+ + Cl-
*May 11, 2014*

**chemistry**

Ionization of an acid in water is typically the formation of hydronium ions, H3O+ and the associated spectator ion. Example: HCl + H2O -> HH3O+ + Cl- (A) Hydrobromic acid: HBr It is very similar to ionization of hydrochloric acid above. For the rest, the reactions are ...
*May 11, 2014*

**Science help please**

Hints: Trachea is a part between the throat and the lungs. The alveoli perform the major function of the respiratory system, namely exchanges intake of fresh air (O2) with waste carbon dioxide (CO2). They are also the ultimate destination of intake of fresh air.
*May 10, 2014*

**Physics**

Note: the degree symbol is written as & d e g ; (suppress all spaces) Difference in elevation, Δh = 270m × sin(6.5°) total mass (cyclist + bicycle), m = 95 kg total weight = mg Work done (on cyclist & bicycle) =mgΔh Component of force along slope, F = mg ...
*May 10, 2014*

**Physic**

Assume diver is 8.2 m below surface (and not 8.2mm), and at the surface, P=101.3 kPa. Pressure below surface =ρgh =1000 kg/m² * 9.8 * 8.2 + 101.3 = 80.36+101.3 kPa = 181.66 kPa Assuming temperature below water and at the surface are identical, use Boyles law: P1V1=...
*May 10, 2014*

**calculus**

Unless I am mistaken, the paraboloid looks like a mountain, tapering off to zero along a circle of radius 3. The cylinder has a radius of 2 and its axis is along the z-axis. So the volume of the paraboloid outside the cylinder is like you drilled a vertical hole of radius 2 ...
*May 10, 2014*

**calculus**

First find out where z(x,y) intersects the x-y plane, which turns out to be a circle given by x²+y²=9 So you would need evaluate the volume of the paraboloid above the x-y plane between the circles x²+y²=2² (cylinder, radius = 2) and x²+y²=3&...
*May 10, 2014*

**Plz, check my answers.**

#1 is not correct. Breaking down large molecules into smaller ones helps the body absorb nutrients from different kinds of food. #2 The circulatory system has the main function of collecting carbon dioxide excreted by cells in different parts of the body and exchange for ...
*May 10, 2014*

**Science**

1. incorrect Food gets digested in the stomach, and nutrients absorbed in the small intestine, and finally excess water extracted in the large intestine. 2. Not sure about the "two servings", and the left and right. 3. incorrect. It is used for grinding hard food, ...
*May 10, 2014*

**Science-3 question**

#1 incorrect. Question asks which function is not one of the circulatory system. #2. incorrect. Blood has the dual function of supplying oxygen to different parts of the body and also to exchange excreted carbon dioxide with oxygen of fresh air. #3. correct.
*May 10, 2014*

**Engineering skill**

Are you able to understand the problem without the accompanied plan/sketch? If you can, kindly describe what you understand in words, or post a link to the plan. Thank you.
*May 10, 2014*

**physics**

Since the question asks for time in the air and distance from the building, we will use vi (initial velocity) as a parameter, and solve accordingly. Assume: '=feet fps=feet per second g=32.2 m/s² vi=initial velocity in fps Horizontal component of velocity, vih =vi cos...
*May 10, 2014*

**physics**

What are being asked depends on the initial velocity. Do you know the velocity, or you are expected to come up with an algebraic expression in terms of the initial velocity? Is the ball thrown at 60° above the horizontal?
*May 10, 2014*

**Algebra 2**

an=8n Substitute n=1,2,... a1=8*1=8 a2=8*2=16 ... guess you can take it from here.
*May 10, 2014*

**physical**

Write "brake", and "braking" when stopping a car. m=2500 kg vi=25 m/s vf=0 t=20 s vf=vi+aΔt 0=25+a(20) solve to get a=-25/20=-5/4=-1.25 m/s² Use Newton's second law to get force force, f = ma =2500 (-1.25) N =-3125 N Ignore the negative sign ...
*May 10, 2014*

**Math (Calculus)**

The challenging part of this problem is to find the limits of integration, which is the intersection of the two curves. As a hint, they meet at x=1.9 and 4.5 (approximately. You can use Newton's method or other iterative methods to improve the solutions. After that, the ...
*May 9, 2014*

**Algebra**

Ratio of 80% and 30% acids is 62-30:80-62 =32:18 =16:9 To make 50 L of 62% Volume of 80% acid = 50*(16/25)=32 L Volume of 30% acid = 50*(9/25)=18 L
*May 9, 2014*

**Calculus**

For #1, y′= x(1+ y) write y'/(1+y) = x put p=y+1 p'/p = x ln(p) = x²/2 + C p=ex²/2+C y=ex²/2+C-1 =Cex²/2-1 or =Cex²/2
*May 9, 2014*

**calculus-answer check**

Oh, sorry, I had the two terms divided and not multiplied.
*May 9, 2014*

**calculus-answer check**

I do not have the same value as yours. Can you post the derivative?
*May 9, 2014*

**physics**

Newton's second law: F=ma if F and m are both identical, the a would be the same, where a=deceleration in m/s². Using the kinematic equations for the first car, vf²=vi²+2aΔx vf=final velocity=0 vi=initial velocity Δx=stopping distance and solve ...
*May 9, 2014*

**ALGEBRA**

Not sure what your choice is, and also if the actual question should read: Y(x)=sqrt(x+4)-3 or Y(x)=sqrt(x+4-3) [as you had it] Can you check if there is a typo?
*May 9, 2014*

**ALGEBRA**

I suppose you mean Y(x)=sqrt(x+4)-3 in which case you can evaluate the function for the various given values and see which one, if any, gives Y(x)=0.
*May 9, 2014*

**Chemistry**

[H3O+]=10-4.67 = [BrO-] [HBrO]=0.200-10-4.67 Ka=[H3O+][BrO-]/[HBrO]=2.286×10^(-9)
*May 9, 2014*

**Physics**

Assuming the "semicircular shape" is like the loop of a roller-coaster, and we want the body to complete the circle. At the top of the loop, of diameter d (radius d/2), the velocity must be such that the centripetal force exerted by the rails ≥0, or mv²/(d/2...
*May 9, 2014*

**Physics**

Assuming the first sentence to mean: "A 10kg box is initially at rest on top of a hill 10m above the ground level." I.e. the box is resting at the top of the hill, which is 10 m. above ground level below. Using ground level as zero potential energy, then At top of ...
*May 9, 2014*

**Physics**

Does the missing figure show the mass of the ball? There is centripetal force of magnitude mv²/r (horizontal) and the weight (vertical) of mg to form the resultant tension of the string of 7.7N. r is the horizontal radius, so must be adjusted for the angle the string ...
*May 9, 2014*

**Economics & Statistics**

20 represents the slope. Slope is defined as the increase in y-value divided by the increase in x-value, that is: slope = Δy / Δx
*May 8, 2014*

**math probability**

1/11 is correct. We can do it in two different ways, easy and difficult. Easy way: Pick 2 of the 5-marbles and any of the remainder. 2/12*1/11=2/132=1/66. The two 5-marbles can be arranged in 4P2 = 4!/(2!2!)= 6 ways, so probability = 6* (1/66) = 1/11 The difficult way: We ...
*May 8, 2014*

**Physics**

Correction to equation (a) W=kx^2 ÷2 (watch units) (b) use same equation, with W=50 ft-lbs = 600 ft-in. solve for x.
*May 8, 2014*

**Physics**

(a) W=kx^2 (watch units) (b) use same equation, with W=50 ft-lbs = 600 ft-in. solve for x.
*May 8, 2014*

**Chemistry - Science (Dr. Bob222)**

Some of the heat generated would have been diverted to convert 2H2O(l) to 2H2O(g), so heat generated would be reduced by 2*40.7=81.4 kJ/mol. Can you take it from here?
*May 8, 2014*

**Trig**

Use: cot(θ)=cos(θ)/sin(θ) sin²(θ)+cos²(θ)=1
*May 7, 2014*

**chemistry**

C1V1=C2V2 (a) 1.0 mol/L * 0.2L = C2 * 1.0 L Solve for C2 (b) C2 (from a) * 25 cm³ = (1.6 mol/L)*V2 Solve for V2.
*May 7, 2014*

**Physics**

Calculat the distance d (metres) it hits the ground when there is no wall. Use reflection to calculate the bounce off the wall. Then case 1: if d>10 m. Ball hits ground at (d-10) before the wall. case 2: if d<10 m. Ball hits ground at d m. from the girl.
*May 7, 2014*

**Java**

This is different from public, or private. Sometimes it is call package or default access. Read up at: http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
*May 7, 2014*

**physics**

use mv²/r = mg solve for v.
*May 6, 2014*

**Data Structure**

Assume the boat and the boys are on the same side of the river at the start and finish. To get one villager across, the two boys must row over, leave a boy on the other side, row back alone, let a villager row over, then then boy on the other side will bring the boat back, ...
*May 6, 2014*

**chemistry: please check work**

Procedure should be correct, did not check the calculations.
*May 5, 2014*

**math**

If the assumption is that the population growth is constant at 4.5%, then Let x=population in 2000, 8791894=x*1.04510 Solve for x.
*May 5, 2014*

**Math**

transpose terms to the form y=ax+b, then a is the slope and b is the y-intercept. 6x=y+1 becomes y=6x-1, compare with y=ax+b and find what a (slope) and b (y-intercept) are.
*May 5, 2014*

**algebra**

Translating in English, you have defined a universal set of integers from one to ten. Then you defined sets (presumably belong to the universal set) which combine ("unioned") to form a new set. The first, {x|x is multiple of 2} means the set of even numbers between 1...
*May 5, 2014*

**chemistry**

Use: C1V1=C2V2 Measure all concentrations in mol/dm^3, and volumes in dm^3 2.0*V = 0.5*2.5 V=1.25/2=0.625 dm^3 or, approximately, 0.63 dm^3 rounded to 2 significant figures.
*May 5, 2014*

**Programming**

Do you need help with the flow-chart, algorithm, the coding or debugging? It would be best for you to tell us what you have learned, and what you have done so far.
*May 5, 2014*

**math mrs. sue HELP!!!**

Say you have a data set {4,6,8,9,10} 1. Find the mean = (4+6+8+9+10)/5=7.4 2. Sum the deviations from the mean (absolute values, no negatives) |(4-7.4)|+|(6-7.4)|+|(8-7.4)|+|(9-7.4)|+|(10-7.4)| = 9.6 3. Divide the sum by the number of data (n=5) to get 9.6/5=1.92 4. 1.92 is ...
*May 4, 2014*

**Math**

Use comparison method: 6-x=y=x-2 means 6-x=x-2 Solve for x and substitute into the original equations to solve for y.
*May 4, 2014*

**math**

Your work is correct, but probably made some mistake with the calculator. Volume = πr²h*1.06 = π(51)^2(120)×1.06; =330847.2π =1039387.133 mm³ approximately.
*May 4, 2014*

**engineering**

For the experiments to verify water-cement ratio, go with Bob Pursley's idea. Water is necessary for the concrete to set, but too much water will weaken the concrete. Too little will make it unworkable, and will end up having voids. Plastisizers are usually added to ...
*May 4, 2014*

**Science**

Weight = total air resistance, so by Newton's first law, the skydiver free-falls at uniform (terminal) velocity.
*May 4, 2014*

**Algebra 2**

Games are random processes. All we can say is that if he wins, he gets one point, and if he loses, he loses one point. We also know (or believe) that the probability of winning or losing is each 50%. The actual outcomes depends naturally on chance. But in the long run, the ...
*May 4, 2014*

**Algebra 2**

oops The probability on the second line should read 0.5 (not negative).
*May 4, 2014*

**Algebra 2**

Find probability of numbers matching (2/4) and not matching (2/4). Construct table for A: Outcome value,x P(outcome) x.P(x) Win..... +1 ...... 0.5 ....... 0.5 Lose.....-1 ...... -0.5 .......-0.5 Sum(x.P(x))=0, so game is fair.
*May 4, 2014*

**Chemistry**

Let K=[HI]²/([H2][I2]) The given reaction is in equilibrium at 430°C, if K=Kc=54.3 Substitute given concentrations to get K=[HI]²/([H2][I2]) =0.5²/(1*1) =0.25 < 54.3 Therefore the reaction is not in equilibrium and will proceed in the forward direction ...
*May 4, 2014*

**Algebra**

Divide each term of the numerator by 2m^3: -6m^9/(2m^3) = -3m^6 -6m^8/(2m^3) = -3m^5 -16m^6/(2m^3) = -8m^3 Choose your answer accordingly.
*May 4, 2014*

**Precalculus**

Yes, the square bracket means the value is included in the interval, and ( or ) means excluded. There are other notations where ( or ) is replaced by a square bracket pointing outwards, for example, [0,2π) is the same as [0,2π[ To solve the above problem: cos^2x=2+2sinx ...
*May 4, 2014*

**Geometry**

π is equivalent to 180° So 7π/4=7*180/4=315°
*May 4, 2014*

**Trignometry**

Since it is a rational number, the numerator and denominator can be replaced by integers. Using (b), you can create any integer, and using (a), you can divide the two numbers, which means you can create any rational number. Hope that helps.
*May 4, 2014*

**Trignometry**

Assuming (c) is the equivalent of the original question: "given any positive rational number q, show that pressing some finite sequence of buttons will yield q" then we need a transformation from q -> q using the given functions. We look for mapping R to R, or ...
*May 4, 2014*

**Math**

The important term to consider is 60(1/3)^t, which has a domain of R (all real) and a range of (0,+∞). Therefore dom T(t) = R ran T(t) = (10,∞)
*May 4, 2014*

**Math**

The model is an exponential function such that e^rt=(1/2) where t=14 hours. e^(14r)=1/2 14r=ln(1/2) r=ln(1/2) / 14 =-.04951 (approx). In 22 hours, factor=e^(-0.04951*22) =0.336475 approx.
*December 14, 2013*

**math**

Step 1: Define variables: c=number of cars t=number of trucks "a dealer has 30 cars and trucks" translates to c+t=30 which means t=30-c .....(1) "If 2 more cars are delivered, the dealer will have 3 times as many cars as trucks." translates to c+2=3t .....(...
*December 14, 2013*

**Math - Trig**

Assume the observations were made from the same building. Let the distance of the building from the tree is D in m. Then D(tan22+tan50)=150 D=(150)/(tan22+tan50)
*December 14, 2013*

**CHIMIE - English translation of question.**

90 mL of 1.5N BaSO4 is mixed with 75 mL of 0.6M Na2SO4. 1. Calculate the ionic force of the resulting salt solution. 2. Deduce the value of the activity coefficient of Na+. Thank you. Rahil: SVP vérifiez si les valeurs sont bien 1,5N et 0,6M (surtout le mélange ...
*December 14, 2013*

**SAT Math**

An example problem could be: between 1 and 1000, how many numbers are neither divisible by 2 nor by 3. So from 1 to 1000, 500 numbers are divisible by 2 (even numbers), and from 1 to 999, there are 333 numbers divisible by 3. However, between 1 and 996 (next number is 1002)...
*December 7, 2013*

**physics**

It depends on the speed of the plane if the frame of reference is terrestrial, namely if the object is considered stationary on firm ground. If the frame of reference is the airplane itself, which cruises at a constant speed in rectilinear motion relative to the terrestrial ...
*November 29, 2013*

**MATHS**

If you are working on number theory, look up Chinese remainder theorem. If you have a puzzle or problem to solve, you can do it as follows: If we took one apple from the box, then the number of apples must be divisible by 2, 3, 4, 5, and 6. Therefore the number of apples would...
*November 27, 2013*

**german**

I do not speak German, but the little I know tells me that the "other" verb is placed at the end of the sentence, such as: Ich muss dort Deutsch sprechen. There I must speak German. One of our math teachers speaks fluently German. Hope he can give you a more detailed...
*November 27, 2013*

**math**

Bill amount * (1-0.03) to give the discounted amount, then add 6% tax Bill amount * (1-0.03) * (1+0.06) For $26.14, the final amount comes to $26.88, after rounding.
*November 27, 2013*

**trig.**

The tree top is 100*tan(52) feet higher than the person's eyes. To get the height h, above ground, h=100tan(52)+5 feet = 133 feet, approximately
*November 27, 2013*

**Physic: Projectile Motion**

let α be the angle of the projectile with the horizontal as it leaves the muzzle. Here α=0 degree. Let vi=initial muzzle velocity, then horizontal velocity, vh=vi*cos(α). Time taken to reach the target t=Horizontal distance/vh where horizontal distance = 100m...
*November 26, 2013*

**Math**

To find the x-intercept, let y=0 and solve for x in 3x=12, or x=4. So the ordered pair would be (4,0). Follow similar rules for the y-intercept.
*November 18, 2013*

**math urgent**

Use your calculator to find 26×56. Since they are both raised to the 6th power, if you are interested in mental calculations, you can apply the law of exponents and multiply the two bases before raising to the given power.
*November 17, 2013*

**algebra**

There are two equations with one unknown, and the two possible solutions are inconsistent.
*November 17, 2013*

**math check**

69 is correct!
*November 17, 2013*

**math - Wish you luck!**

:)
*November 17, 2013*

**chemistry**

M*V=2.01*711/1000
*November 17, 2013*

**Calculus - Optimization**

Good catch, Steve. Thank you.
*November 16, 2013*

**Calculus - Optimization**

Let the size of the square (cross-section) be s. Then we need to maximize V=s²(24-2s) with respect to s. First find the derivative and equate to zero: dV/ds = 48s-6s²=0 means s=0 or s=8 s=0 corresponds to a minimum volume and s=8 corresponds to a maximum volume. So ...
*November 16, 2013*

**Business Math**

Principal, P = $10000 interest per period of 6 months, i = 0.06 number of periods, n = 5 yrs/0.5 yr = 10 Value at maturity =P(1+i)^n He will have money to pay for the Jeep, and perhaps the sales taxes as well.
*November 10, 2013*

**Math**

7×6=42 7×7=49 so there are 6 and (48-42)=6/7 apples, or 6 6/7 apples.
*October 15, 2013*

**Homework Help Calculus**

Problem of units conversion. 0.4071504079 m³ =0.4071504079×10^6 cm³ =407150 cm³ approximately.
*October 15, 2013*

**Algebra 2**

The first equation has a y-intercept of -17. The x-intercept is -17/7=-(2+3/7) =-2.4286 approx. The second equation has a y-intercept of -2.4, and x-intercept of -2.4/(-0.3)=8. If you produce the two lines to intersection, the estimated solution would be (-2, -3)
*October 15, 2013*

**Practice Exam Calculus**

you can use the same approach as for the paint on sphere. A=4πr² dA/dr=8πr ΔA=8πr Δr =8π(20)(1/5) =32π
*October 15, 2013*

**Math**

If you mean (4/8)y - 21 = 3 then y=48 as you got. If the question were (4/8)y-21=0 then y=42
*September 23, 2013*

**Chemistry**

MC12H22O11=342 MCO2=44 C12H22O11+xO2=12CO2+... Ratio of mass of C12H22O11 to CO2 =342:12*44 =342:484 Mass of C12H22O11 that produces 3.6g CO2 =3.6*(342/484) =2.544g Mass ratio NaCl:C12H22O11 =(5.5-2.544):2.544 =2.956:2.544 Calculate mass percentage and reduce to 3 significant ...
*September 23, 2013*

**geometry**

The question defined what complementary angles are, but did not say that a and b are complementary. The question has a solution if a and b are complementary, and will be assumed as follows. if a and b are complementary, then a+b=90 angle a is 21 degrees more than twice angle b...
*September 21, 2013*

**Surveying**

Are you measuring the vertical angle (from the horizon) where 90 degrees is vertically up, or the zenith angle (from zenith, vertically up) where 91 degrees is just below the horizon? A vertical angle of 91 degrees requires a special eye-piece/prism, and is past the vertical...
*September 21, 2013*

**math**

There are 9 choices for each of the first three digits, and 25 choices for the last two digits. Use the multiplication rule to get: 93252
*September 20, 2013*

**statistics**

Use a probability tree: Next person male: 42% wash his hands: 43% female: 58% wash her hands 66% P(wash)=42%*43% + 58%*66% =0.5634
*September 20, 2013*

**chemistry**

When heated: 1. acetic acid phase change 2. sodium bicarbonate decomposition into sodium carbonate, carbon dioxide and water. 3. arsenic trioxide phase change
*September 7, 2013*

**Chemistry**

First establish the combustion equation and have it balanced: C8H18 + O2 -> 8CO2 + 9H2O. Balances for C, but not for O. Since there are 16+9=25O on the right, we need to double the number to make the number of molecules on the left a whole number. So it becomes: 2C8H18 + ...
*September 7, 2013*