Tuesday
September 30, 2014

Posts by bobpursley


Total # Posts: 36,110

physics
correct
September 30, 2014

chemistry
dS = (6.01 kJ mol-1)/272 K * (50 g)/(18 g mol-1) = you do it kJ / K
September 30, 2014

Physics
it must be 2/3 of her weight.
September 29, 2014

physics
the sum of the weights on the scale equals the total weight.
September 29, 2014

physics
380/600=e^-(t/1.5E-6) take ln of each side t = 1.5E-6*.456-6.84E-7 sec speed=distance/time=1900/time above.
September 29, 2014

World History (Please, help me!)
The principle of the french revolution was spread through the napoleonic code. Since Napoleon was able to conquer so many countries he made sure that they were completely abiding by his laws. Within his laws were some true aspects of the french revolution like equality, public...
September 29, 2014

Physics
zero. the electron has to be moving to have a magnetic force.
September 29, 2014

physics
29=vboat+vcar + vcurrent assume vcurrent is zero.
September 28, 2014

community policing
Taylor developed time and motion study, which was loosely called scientific management.
September 28, 2014

Calculus
y'=2^x*ln2 if y=a^x y'=a^x *lna
September 28, 2014

geometry
draw the picture. well, 40=22+3x-5 solve for x
September 28, 2014

physics
vy=vsin45 vx=vcos45 hf=hi-1/2 g t^2+vsin45*t t=2vsin45/g in the air. distance horizontal=vcos45*t 1m=v .707*2v*.707/g 1=v^2/2g v=sqrt19.8 m/s max height: mgh=1/2 m v^2 h=1/2 (19.8)/g
September 28, 2014

Physics HELP
a. time to fall, in the vertical -60=-4.9t^2 solve for t. b,c theta=arctan vf/17 where 1/2 mvf^2=mg60 vf=sqrt120g
September 28, 2014

chemistry
dr Bob is correct on the atomic masses, I wasn't thinking.
September 27, 2014

chemistry
dr Bob is correct on the atomic masses, I wasn't thinking.
September 27, 2014

chemistry
assume 100 grams then moles C= 53.31/12 moles O2=35.51/32 moles H= 11.18/2 now, divide each of those numbers by the smallest one. you may have to adjust the ratios to make them all whole numbers. The remaining numbers are the mole ratios in the formula CxOyHz
September 27, 2014

physics
time to get to screen: time=distance/velocity how far does it fall? d=1/2 g t^2
September 27, 2014

Simplify Practice.
I will be happy to critique your work on this.
September 27, 2014

chemistry
I am wondering what you are having difficulty with. a. write and balance the equation b. note the mole ratio of C to O2 c. check the mole ratio of the amounts given. d. if the given mole ratio is greater than b, then you have C in excess
September 27, 2014

Check my answers? Math help.
4 is wrong 5 is wrong.
September 27, 2014

CHEM
Bong? What is the question here? I suspect on carbon 2 there is one H, and on carbon 3 and 4 there are two H on each carbon. This is 1-Pentene https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTx7bv5djkgFs7ik1olOykunOXE51Mp-L2G2QKMyNLCpcAUIK9j
September 27, 2014

physics
Is there a question here?
September 27, 2014

chemistry
H+=.05*1+.1*.2-.5*.01*2-.2*.1=.04moles check that.
September 27, 2014

physics
vf^2=2ad solve for a
September 27, 2014

physics
v^2/r=1.6 m/s^2 find v then, period v=distance/period period=2PI*r/v
September 27, 2014

Chemistry
Hess' Law: Hr=--635.1 kJ-393.5kJ-(-1205.9)kJ In my head, looks like about it is endothermic (absorbs heat). I bet that is why limestone has to be heated in a furnace to make quick lime.
September 27, 2014

Physics
distance is 1/2 a t^2, in this case t=V/a) recheck it, I do periodically make errors when typing math.
September 27, 2014

Physics
car A: v=at1 or t1=v/a total distance traveled d=1/2 a*t1^2+v(t2) = 1/2 (v^2/a) + v*t2 car B: distance=1/2 ab*t2^2 but the distance they travel are the same, 1/2 ab*t2^2 =1/2 (v^2/a)+v*t2 Now the problem we have is what is accelearations a, and ab? You cant solve for three ...
September 27, 2014

astro
b1 / b2 = (2.512)^(m2-m1) so you are looking for b1/b2 = 2.512^(11.05+.01)=about 27,000 You do it more accurately
September 27, 2014

physics
http://en.wikipedia.org/wiki/Doppler_effect doppler shift depends on the relative difference between the source and the receiver, in this case, no relative motion, so no doppler shift.
September 27, 2014

physics
vf=vi+at but a=- force/mass=-mu*mg/m=-mu*g the negative sign indicates oposite direction to movement solve for Vf
September 26, 2014

workshop
The best answer I could ever honestly say was, I will have to think on that, as most of what was presented was of not much immediate use to me.
September 26, 2014

Calculus
I am uncertain what you are doing. Estimating is easy on a calculator, put in values of x close to zero as you did on the .0001, .001, and press equals on your calculator. I have no idea why you averaged values values to get .597 Now, later in Calculus, you will learn L'...
September 26, 2014

Math
rule: divisibile by 9: sum of digits is divisible by 9 (2+3+4+0)=9 divide it out and see.
September 26, 2014

Pre-Calc
17 Nonrigid Transformations Rigid transformations: the basic shape of the graph is unchanged . Horizontal shifts, Vertical shifts, Reflections Change only the position of the graph in the coordinate plane. Nonrigid transformations: cause a distortion — a change in the ...
September 26, 2014

Physics
Force=kx x=force/k=910/13500 meters
September 26, 2014

physics
at the top, vertical velocity is zero h=vi*t-1/2 g t^2 7000=vi*t-16t^2 this is a quadratic, solve for time. Initial KE=final PE 1/2 m v^2=mgh solve for v, the initial velocity how long is the flight? Twice the time to the top.
September 26, 2014

physics
hf=hi+vi*t-1/2 g t^2 hf=0, hi=1.5 , vi=19 solve for t. It will be a quadratic.
September 26, 2014

Physics
The distance they flew is the same, in the same time. da=vi*t+1/2 at^2=4800t-16t^2/2 db=vi*t+1/2 at^2=9000t+at^2 /2 set them equal t(4800-8t)=t(9000+at/2) 9600-16t=18000+at t(a+16)= -8400 so you see here, there is no unique solution. The faster B breaks, the sooner the rockets...
September 26, 2014

Physics
a. -9.8m/s^2 b. d=vi*t+ 1/2 at^2=-7.56*t-4.96t^2
September 26, 2014

Physics
friction=mu(mg) 3E8dynes*1E-5N/dyne=mu*50*g solve for mu, the coefficent of friction. Now on a tilt: force gravity down the plane: mgSinTheta force normal to the plane: mgCosTheta friction force=mu*force normal so if you tilt it to sliding, forcedownplane=friction mgsinTheta=...
September 26, 2014

arithmetic
expected gain: 4100/1700 -cost of ticket = 4100/1700 - 25= figure it out So buying more tickets will not make you more money, if fact, you lose more
September 26, 2014

MATHS
A(t)=Ao*(1/2)^(t/1590) A(t)/Ao=.5^1/1590 = put this in the google search window: .5^1/1590 =
September 26, 2014

physics
Wonder where the return current is flowing? Ground? Ok, assuming power can be transmitted by only one wire, then Ampere's law applies INT B.ds=mu*I B*2Pi*10=mu*200 solve for B
September 26, 2014

Pre-Calculus
1 reflection 2. shift it right three units.
September 26, 2014

Science: Acids that affects the tooth enamel
Vinegar, carbonated beverages (carbonic acid), gluconic acid, citric acid (lemonaide). Tartaric acid is another.
September 26, 2014

floral design
Fall flowers? Outdoors? Jewel Tones Bold? available in the fall are flowers in Brown, Gold, Yellow,
September 25, 2014

Math! URGENT
If you solve for x in that equation, how many solutions do you get: SOlve it, then which is true... one, two, infinite, none?
September 25, 2014

physics
Hmmm. half the speed of sound? then the relative velocity would be .5, or f=fo*1/2
September 25, 2014

trignometry
Draw the figure. draw a line from X angle perpendicular to side x. Note then that zsinY=ysinZ or z=ysinZ/sinY now draw a line from angle Y to side y perpendicular to y. Note that area=1/2 bh=1/2 y*zsinX then area= 1/2 ysinX*ysinZ/sinY QED
September 25, 2014

Math! URGENT
-9-6(w+5) -9-6w-30 -6w-39
September 25, 2014

Math! URGENT
yes, of course
September 25, 2014

Chemistry
a. determine and find the following heats. heat to bring coffee from -15C to 0 heat to melt coffee at 0C heat to heat coffee to 95C add them. Milk? she didn't ask for any. Real chemistry profs drink black coffee.
September 25, 2014

Algebra
a. C=K-273 b. K=100+273 c. K=-40+273 Your teacher is much too easy.
September 25, 2014

Chemistry
heat=mc deltaT deltaT=74.0/(500*2.46)= ? now final temp, equals initial temp 25C + deltatemp
September 25, 2014

science
volume of what? what is its density?
September 25, 2014

physics
I suspect optics is pretty important.
September 25, 2014

physics
what is 10sin10deg ? not certain what "straight up" means, I assume it means along.
September 25, 2014

chemistry
You are almost correct on the mass difference, however it is negative (-.253807 amu) as the mass of products is greater than reactants, so high energy was required in the form of high KE in the Nickel atom. Converting that to energy needed for the reaction, correct, -4.2145x10...
September 25, 2014

Algebra 2
the four moves it vertically 4 units. the x-2 shifts it to the left, two units
September 24, 2014

Pharmacy Calculations
total amount=45 grams amount cortizone=.025*30 CORRECTION ratio=amountcortizone/total
September 24, 2014

Pharmacy Calculations
total amount=45 grams amount cortizone=.0025*30 ratio=amountcortizone/total
September 24, 2014

Math
the debt owed, 50 dollars, is to be divided by five college girls.
September 24, 2014

math
lateral area is the area of the four faces. area=(lw+lh)*2 notice end areas are not in lateral area. compute h, you know l, w, and area.
September 24, 2014

math
693=A*8.7+C*5.4 but C=3A solve for A, and C
September 24, 2014

Calculus
a has to be instructions for b, and c. b. rate change=change/time=(6.2-6.8)/(9-3) c. rate change=change/time=(7-6.8)/(9-5)
September 24, 2014

Chemistry
look up the atomic mass of Ar. atomicmassAr=.34*35.9675+x*39.9624+(1-x-.34)35.9675) solve for x, you know the avg atomic mass of Ar, from the periodic table.
September 24, 2014

physics
parallel down=m*g*SinTheta correction here, sine, not cosine. the friction on the plane down the plane is mu*mg*CosTheta
September 24, 2014

physics
parallel down=m*g*cosTheta
September 24, 2014

Physics
energy=number(plancks constant)*frequency now you have an issue with the problem. Power emitted is given, so you cannot find the number of photons,so number is actually going to be number of photons per second power=photons/second* plancksconst*freq
September 23, 2014

physics
vf^2=vi^2+2ad but a= force/mass you know vi=0 vf-.577m/s,and you know d. solve for force.
September 23, 2014

ratios
.8/1/6= 4.8/1 or on whole numbers 48/10
September 23, 2014

Math
depth=8mm-.12x where x is thousands of miles 2=8-.12x x=6/.12=50 ?
September 23, 2014

Physic
frequency=4cycles/7seconds velocity=frequency*wavelength = 4/7 * 2*17.3 cm/sec change to m/s
September 23, 2014

Physics
PE=mgh=massabove*g*50 Joules
September 23, 2014

History
And then again, maybe MsSue is right, but I suspect salty land played an important part.
September 23, 2014

History
http://en.wikipedia.org/wiki/Sumer#Decline The actual reason is that population went north, more dependence on irrigated fields, so the soil got more and more salty, and production decreased. You have to flush soils in irrigated lands, especially in hot arid regions (like ...
September 23, 2014

math
d z/dy= d/dy e^y sin(xy) = sin xy * e^y + cos(xy)*d(xy)/dy *e^y but d(xy)/dy=x so there it is.
September 23, 2014

Physics
force=mass*acceleration acceleration=force/mass=mu*mass*g/mass = mu*g Vf=vi-a*t=vi-mu*g*time
September 23, 2014

algebra
Plan1=450+.03Sales Plan2=300+.16Sales set them both equal, solve for sales.
September 23, 2014

physics
speed=2PI*radius/period so you want period in seconds... 29.50yr(365.25 days/yr)(24hrs/day)(3600sec/hr)= period in seconds
September 22, 2014

Basic math question
divide by 2: 2,4802 2,2,2401 2,2,7,343 2,2, 7,7,49 2,2,2,7,7,7,7 taking the even pairs of roots out: 2,7,7, sqrt=98
September 22, 2014

physics
you have velocities, times, bearings. so you can get distances and bearings. Add those two vectors.
September 22, 2014

Calculus
b. 76=40+60cos(PI/6 (t-2)) .6=cos(theta) theta=arccos.6=.972 rad .972=PI/6 (t-2) solve for t. c. evaluate dh/dt=-60*PI/6*sin(PI/6(t-2) at the t in b. is it negative? then level is going down. Positive, increasing. find times when h=0, then check between those times. your graph...
September 22, 2014

Physical Science
I would convert 20,000 km to grams. 2E4kg=2E7grams momentum locomoative=2E7*40 gKm/hr momentum fly= 1*8.40E8 gkm/hr momentum locomotive=8E8 gkm/hr momentum fly=8.4E8 gkm/hr
September 22, 2014

Chemistry
add the volume of the cylinder, PI*r^2*h r=1.9cm, h=5.4cm.
September 22, 2014

trigonometry
speed=distance/time=PI*diameter/(1/60 min) = PI * diameter*60 inches/minute
September 22, 2014

Math
what are the factors of 777? 7, 111 7,3,37
September 21, 2014

physics
Horizontal? 18.2 cosAngle
September 21, 2014

Chemistry
density=mass/volume=mass/LWT T=mass/(L*W*density) change yards to cm, inches to cm first. density should be in grams/cm^3, change kg to grams...
September 21, 2014

physics
the acceleration is always g, as the force on the ball from earth is constant.
September 21, 2014

Pshyics
.12*50-(masschain+.12)(31)=0 from summing moments about the end. solve for masschain.
September 21, 2014

Physics College - Circular motion
The magnitude of acceleration is constant, and the direction is towards the center. So you are given two values of acceleration in directions which intersect at the center of rotation. mag acceleration= sqrt(36+16)=sqrt(52) The next step is to find the displacement between ...
September 21, 2014

physics
No friction? a=g*sinTheta
September 21, 2014

Fluid Mechanics
density=mass/volume= mass stuff= 1/4 4.6 kg if I read your statment correctly. I am uncertain if when it is said the "mass of the cylinder" that means the cylinder with the stuff, or the cylinder itself. I took it as the cylinder with the stuff. densiy= (.25*4.6)kg/(...
September 21, 2014

Fluid Mechanics
volumesteel=.85/7.1 * volume cone volumesteel=.85/7.1 * 1/3 *(pi*25)20 so the edge of a cube of steel would be the cubic root of that.
September 21, 2014

maths
If you sketch it , you know two sides, and the included angle. Law of cosines to get the third side QR, and then the law of sines to get the interior angles, and for the final bearing, you should be able to add the angles to figure it.
September 19, 2014

p.e
For a student, C is probably the best solution. Depression is a very complex issue, kids just dont have the experience to be counselors. B is definitely wrong.
September 19, 2014

History
Frankly, I like B and D better. Of the two, D is probably better than B, if one includes with reading and writing skills education. Missionaries taught Indians in the EAst, but later, for the Plains indians, the Govt took it over, it was the job of the Indian Agent, and they ...
September 19, 2014

physics
acceleration=(vfinal-Vinitial)/time Now, notice the velocity is vectors. I would do it like this vf=9.75cos25 S + 9.75sin25 E Vi=8.64sin35 S + 8.64cos35 W remember W is -E, so when you subtract.. Vf-Vi=(9.75cos25 -8.64sin35)S +(9.75sin25+8.64cos35) E do that math, divide by ...
September 19, 2014

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