Saturday

April 19, 2014

April 19, 2014

Total # Posts: 16,161

**statistics**

Here is an online normal distribution calculator: http://davidmlane.com/hyperstat/z_table.html

**statistics**

well, you have enough data points to use normal distribution rather than computing with binomials forever and a day. Otherwise use a program or spreadsheet to compute all the binomial coefs and powers and products mean = n p = 200 * .6 = 120 sigma^2 = 120 (.4) = 48 so sigma = ...

**Math**

we have already done a half life one but anyway ds/dt = k s ds/s = k dt ln s = k t + c when t = 0, ln si = c si is initial size ln s = k t + ln si ln (s/si) = k t s/si = e^kt 2 = e^k(30 min) ln 2 = 30 k k = .0231 1,000,000/50 = e^.0231 t ln (20,000) = .0231 t t = 428.6 = 429 m...

**Math**

.5 = e^-k T ln .5 = - k T T = -.693/-k = .693/k b) T = .693 / .0001074 = 6454 years

**physics**

1 C 2 less, maybe you run over the mark from the first one on the track just as the rear can explodes, and the two marks on the track are together :)

**Physics**

On earth I assume weight on first line = (86.4+20.8)(9.81) weight on second (lower) line = 20.8 (9.81)

**physics**

in the horizontal direction the ball has no acceleration once let go (no horizontal force) so now it is 9 m/s^2 down by the way, g on Mars about the same as earth ? FALSE

**physic**

40 g = .04 kg .04 [25 (sh ice) + heat of fusion + 100 (sh water) + heat of vaporization + 5 (sh water vapor at 1 atm) ]

**algebra 2**

An = A1 + (n-1)d average = (A1 + An)/2 sum = average * number of terms = n (A1 +An)/2 = (n/2) [ 2 A1 + (n-1)d ] here = (11/2) [ -24 + (10)5 ] = (11/2) (26) = 11 * 13 = 143

**physics**

z = 5 * 10^5 ohms i = 1/(5*`10^6) = .2 *10^-6 = 2 *10^-7

**physics**

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/rlcser.html

**English**

B. ok C. Based on his very frail appearance, a mugger might SURMISE that he would be SUSCEPTIBLE to a strong arm attack; however, that would be a great mistake.

**English**

My version A. I said that he was HYPOCRITICAL because he pretends to be filled with PIETY, but I know that he is a bigger sinner than I am. I wouldn't even mind that if on Sundays in church he wasn't so POMPOUS.

**social studies check answers**

1. disagree 2. no idea 4. agree

**English**

loud and intense manner.

**algebra**

.25 A = 48 A = 48/.25 = 48 * 4 = 192 (2/3) 192 = 2 (64) = 128

**Read what you typed**

Lots of dimensions missing.

**Math**

ds = sqrt (dx^2 + dy^2) dx = -5sin t +5 sin5t dx^2= 25sin^2 t -50sint sin5t+25sin^2 5t dy = 5 cos t -5 cos 5t dy^2= 25cos^2 t-50costcos5t +25 cos^2 5t luckily sin^2 + cos^2 = 1 dx^2+dy^2=50-50(sin t sin 5t+costcos 5t) but sin a sin b + cos a cos b = cos(a-b) = 50 - 50 cos 4 t ...

**Physics**

delta L/L = (T/area) / E = (215*9.81 /2*10^-5) / 8*10^10 = ( 1054 * 10^5 ) / 8*10^10 = 132 * 10-5 so delta L = (3.5)(132*10^-5) = 461 * 10^-5 = .00461 meters = .461 cm

**Physics**

Tension in cable = T Force up at end from cable = T sin 37 compression Force toward wall = T cos 37 max friction force = .485 T cos 37 up vertical forces on rod sum to 0 2 Fg = .485 T cos 37 + T sin 37 2 Fg = .989 T T = 2.02 Fg take moments about intersection of rod and wall c...

**Physics 141**

Hey. I just did that.

**Physics 141**

Distance axle above step edge = .33 - .125 = .205 Angle T is angle between straight down from Axle and the top edge of the step so cos T = .205/.33 T = 10.58 deg sin T = .184 Take moments about the top edge of the step. F * .205 clockwise (my step is on the right) m g * .33 si...

**Physics 141**

T = 1/4 so f = 4

**Physics 141**

after one period T, (8 pi T) = 2 pi so T = 1/4 so f = 1/T = 4

**math**

first .2*9.45 = 1.89 remaining length = 9.45 - 1.89 = 7.56 so piece 2 + (piece 2 - .12) = 7.56 2 * piece 2 = 7.68 piece 2 = 3.84

**Civil War**

It did sort of.

**strange question but**

You can easily figure out the velocity of each. It has nothing to do with the mass. (1/2) m v^2 = m g h note m cancels v = sqrt (2gh) so for example for 2.5 meters v = sqrt (2* 9.81*2.5) = 7 meters/second -------------------------- The only force here is gravity itself F = m ...

**physics**

(1/2) L i^2 = (1/2) C V^2 i^2 = (C/L) V^2 i^2 = (3.1*10^-6 / 5.6*10^-3) (961) i^2 = 532 * 10^-3 = 53.2 * 10^-4 i = 7.3 * 10^-2 = .073 amps

**physics**

period = 1/frequency = (1/7.01)*10^-18 wavelength = 3*10^8 (1/7.01)*10^-18 = .428 * 19^-10 = 4.28 * 10^-11 meters

**Statistics**

I also agree

**Pre calculus**

if it is x^3 + 2 x^2 - 15 x + 20 = 0 then: http://www.mathportal.org/calculators/polynomials-solvers/polynomial-roots-calculator.php gives x = -5.44 x = 1.72 +/- .853 i

**physics. PLEASE HELP**

If it is 50 meters high, the pressure is the weight of a one meter square column 50 meters high. Water density is about 1000 Kilograms/ cubic meter So the mass of this column is 1000 Kg/m^3 * 50 m * g or 1000 * 50 * 9.81 = 490,500 Newtons that weight is spread out over the one...

**Physics**

work done = increase in kinetic energy (here we have a decrease so the work is negative. The force is opposite to the direction of motion) work = (1/2)(4.5*10^4)(5000^2 - 7000^2) work = force *distance moved in direction of force so Force = work/(1.4*10^6)

**Physical science**

k Q1 Q2 / d^2 1) if d2 = 3 d 1 then 1/d^2^2 = 1/(3d1)^2 = (1/9) 1/d1^2 2) k Q1 (2 Q2)/d^2 = twice original

**speech-english**

I am tempted to just say model right off the bat but it depends on the audience and the setting. If it is a big crowd in an auditorium a model might not be very easy to look at from all angles and see inside it. Then photographs or a flip chart might be better. If the opportun...

**Physics**

original east momentum = 2115*10.61 final east momentum = (2115+3169)*5.03cos32.4 22440 = 5284 * 4.25 v = 22440 v v =1 m/s

**physics**

not of the mass itself, but about some other point. For example for a point mass hanging from a nail on a string it is m L^2 about the attachment point at the ceiling where L is the length of the string.

**Math (how do you find the volume of a cone)**

for any object with a point at the top and straight sides use (1/3) height * area of base

**Physics**

r = 1.5 * 10^-3 m pi r^2 = pi (2.25) * 10^-6 m^2 F/A = P = 2*10^4 /[pi (2.25) *10^-6) ] = .283 *10^10 = 2.83 * 10*9 Pascals

**Physics Help**

You have: velocity v = dx/dt = -A*ω*sin(ωt) so what is -A omega ? A = 3.5 omega = 2 pi f = .848 so - A omega = -2.968 or -2.97

**Geometry**

http://www.jiskha.com/display.cgi?id=1396301143

**Math probability**

4+7+3+2 = 16 socks prob red first = 4/16 prob green second = 7/15 prob that happens = (4*7)/(16*15) prob green first = 7/16 prob red second = 4/15 so again (4*7)/(16*15) so in the end 2 * 4 * 7 / (15*16) = .233

**Math**

1/51 I just answered this a few minutes ago.

**Geometry**

equation of circle radius 25 : x^2 + y^2 = 25^2 = 625 now what is x when 15 cm from center (which is ten cm from surface)? x^2 + 225 = 625 x^2 = 400 x = 20 that is our radius at urface area = pi (20)^2 = 400 pi = 1257 cm^2

**science(check answers)**

2 was wrong as were the others I mentioned more mass ---> more pull of gravity

**science(check answers)**

1 A true If you pick a hunk of iron up you want to be able to drop it when you get it to the place you want it. 2 b F = G M1M2/d^2 force proportional to mass 6 c the resistance has to go up to keep the same current R = V/i 7 d i reverses, B reverses

**math**

.9 x = 22,000 x = 22,000/0.9 = 24,444,44

**math**

if the pool is 76 feet long and each tile is 6 feet you need 13 tiles because 12 tiles only goes 72 feet However do you not need other rows of tile? This is a very strange question. Most tiles are about 6 inches, not six feet and they are square and you have to fit them in are...

**Math**

They would have to go 1296 miles in 7 days. 1296/7 miles/day 1296 / (7*24)miles/hour

**Math**

10/510 = .0196

**science(check answers)**

1.D yes 2.A yes 3.A yes 4.im not sure please help V = i R 12 = 4 R , R = 12/4 = 3 Ohms 5.false. I agree but am not sure what it means. One could always have a short circuit where current streams through doing nothing useful.

**Physics**

weight down = m g max friction force = mu m g centripetal force = m (lateral acceleration) mu m g = m a = m (.96 g) a = .96 g We call "lateral acceleration" centripetal acceleration :)

**Physics**

2.1) LOL - I would guess around mu = 0.96 2.2) 120,000 m/h * 1 h/3600 s = 33.33 m/s m v^2/R = .96 m g R = v^2/(.96 g) = 118 meters 2.3) mu = .8*.96 = .768 Normal F = m g cos 15 = .966 m g friction force = mu Normal = .768*.966mg =.742 mg component of weight down slope = m g si...

**Physical Sciences**

Type Mach 2 into Google and get back 681 m/s Ac = v^2/r = (681)^2/5800 = 80 m/s^2 80/9.81 = 8.15 g

**Calculus**

LOL, sketch a graph !

**Physics**

You are welcome :)

**Physics**

ke of ball at bottom = (1/2) m (2.44)^2 = 2.98 m Pe at top = m g h = m (9.81)(h) so 9.81 h m = 2.98 m h = .303 meters h = 1.47 (1 - cos theta) .303/1.47 = 1 - cos T .206 = 1 - cos T -cos T = -.794 T = 37.4 degrees

**physics**

(1/2)(4.008) V^2 = (1/2)(2500)(.037)^2 V = .924 m/s .008 Vb = (4.008)(.924 ) Vb = 463 m/s

**physics**

use conservation of momentum to get the velocity of the total mass (4.008 kg) just after collision in terms of bullet velocity Vb. Call that V. (1/2) m V^2 = (1/2) k x^2 that gives you V go back and get Vb

**Patterns and rules unit test 7th grade**

geometric sequeence a = -2 r = 6 An = a r^(n-1) A5 = -2 (6)^4 = - 2592 A6 = 6(-2592) = - 15552 A7 = 6 A6 = -93312

**Physics**

weight in air = 6400 * 9.81 volume of water displaced = 1 m^3 weight of water displaced = 1000 *9.81 *1 = 9810 N = force up from water tension = (6400 - 1000)(9.81) = 52,974 N

**Physics**

(1/2) m v^2 = .5 * .559 * 2.7^2

**statistics**

first one 12/45 second on 11/44 12/45 * 11/44

**physics**

a) v^2/R b) m v^2/R

**physics**

2000 u = 10 (200 cos 60 ) u = cos 60

**physics**

1500 * 20 = (1500+m)10 m = 1500

**physics**

Because the air we live in also has pressure no pressure change in a horizontal hose with no flow through it.

**physics**

rho g h = 1000 (9.81)(30) = 2.94*10^5 add 1 atm = 1*10^5 and get total of 3.9 * 10^5

**CALC 2**

try similar for the rest

**CALC 2**

1 at start a eats 2/3 ** 1/9 *** 1/54 b eats 1/6 ** 1/36 ** 1/108 first line is geometric series 2/3 + 2/3(1/6) + (2/3)(1/6)^2 ... An = 2/3 +(1/6)^n-1 sum of that series = a/(1-r) = (2/3)/(1-1/6) = 2/3 /5/6 = 4/5

**Physics**

You understand that he used quite different numbers in his example, D = 2.71 diameter 24 liters instead of 25 1.1 instead of 1.4 min

**Physics**

I found it all right. He has a pretty convoluted way of explaining it but it is the same thing. I have no idea why he converted to cm^3 rather than to meters^3 from Liters 1000 Liters = 1 m^3 1 Liter = 1000 cm^3 1 m^3 = 1,000,000 cm^3 but it is standard to work in meters, kg a...

**Statistic**

You are welcome :)

**Statistic**

p(good) = .7 , p(fail) = .3 n = 10 crunch it out with your binomial distribution P(2) for example = C(10,2)*.7^2*.3^8 = 10!/[8!*2!] * .49 * 6.56*10^-5 = 45 * .49 * 6.56*10^-5 = .001447

**physics**

work done = change in Ke = (1/2) m v^2 = 500*900 Joules power = work/time = 500 * 900 / 5 = 90,000 Watts

**math**

2 * 3 = 3 * 2 ????? Commutative

**Calculus Help Please**

f(x) = f(a) + (x-a) f'(a) f(x) = x^4 df/dx = 4x^3 let a = 2 then f(a) = 2^4 = 16 f'(a) = 4*8 = 32 f(x) = 16 + (x-a)(32) x-a = - .001 so f(1.999) = 16 -.001(32) = 16 - .032 f(1.999) = 15.968 with calculator it is 15.968 also

**Math (check answer)**

if you mean absolute value of 7 yes it is 7

**Calculus Help Please!!!**

at x = 3 y = 3*3 - 9 = 0 at x = 2.4 y = 3(2.4) - 2.4^2 = 1.44 delta y = 1.44 -0 = 1.44 dy/dx = 3 - 2 x at x = 3 dy/dx = 3 - 6 = -3 if dx = -.6 dy = -3 (-.6) = 1.8

**Algebra**

.163 x = 47600 x = 47600/.163

**Math**

You are welcome :)

**Math C redone**

should subtract 30 (14*2+2), not 44 c) draw a Venn diagram Only in A1 = 103 - 30 = 73 Only in A2 = 992- 30= 962 Only in A3 = 10011 - 30 = 9981 shared = 3*14 + 2 = 44 sum = 11060

**Math**

a) just add them 11106 b) They are all in A3 so 10011 c) draw a Venn diagram Only in A1 = 103 - 44 = 59 Only in A2 = 992- 44= 948 Only in A3 = 10011 - 44 = 9967 shared = 3*14 + 2 = 44 sum = 11018

**Math**

do you mean y = 18/(x^2-9) ???? if so dy/dx = -18 (2x)/(x^2-9)^2 0 at x = 0 In that interval the bigger |x|. the more negative the function so it is max when x = 0 18/-9 = -2 so C

**math**

You are welcome, good luck.

**math**

25 * .65 = 16.25 25 * 0.65 * 0.2 = 3.25 but I do not believe that 0.2. I think you have the loss 80% when it should be like 20%

**math**

the cooking loss is 80% ??? that does not sound right but if you are serious then 25 * (1-.35) (.2)= 25*.65*.2 = 3.25 pounds

**Algebra**

x^2 + (2x+20)^2 = (2x+22)^2 x^2+ 4 x^2 + 80 x + 400 = 4 x^2+88x + 484 x^2 - 8 x - 84 = 0 (x-14)(x+6) = 0 x = 14 2x+20 = 48 2x+22 = 50

**physic**

Plus charges flow to one side, minus charges to the other.

**Calculus Help Please!!!**

Oh, I see f(x) = ln (1+x) df/dx = 1/(1+x) d^2f/dx^2 = -1/(1+x)^2 f(x) = f(0) + [1/(1+0)] x - x^2/2! ... f(x) = 0 + x - x^2/2 + ..... well at a first cut when is x^2/2 =.1 x? x/2 = .1 x = .2

**Incomplete!**

Linear approximation to what function? Did you try to copy and paste? If so, that does not work here.

**Physic**

zero The plus charges on one side exactly balance the - charges on the other side. If you for example had more plus charges on one plate then they would attract negative charges to the opposite plate and would cause a flow across. Moreover the entire capacitor would then have ...

**Science**

I do not understand what the second question means? Balance the equations or what?

**Science**

Al is +3 here 2 Al + 2CuCl2 --> 2AlCl3 + 3Cu

**Math**

look for where second derivative is positive. ( x <0.75) https://www.wolframalpha.com/input/?i=second+derivative+of+-1%2F%28x-.75%29

**Physical Science 9**

Incomplete combustion ---> carbon particles and CO instead of CO2 That is not a good question by the way. You should know that for sure. The other things happen in: plants stomachs compost heaps and coffins not power plants

**Physics 112**

a) as t--> oo inductor is a short circuit, no reactance so V = i at big t * R V = (8.4)(.26) = 2.14 Volts b) at t = 0, i = 0, so all voltage across L 2.14 = L di/dt let i = 8.4 [ 1 - e^-t/tau ] given tau = .1 s i = 8.4 [ 1 - e^-10 t ] di/dt = 8.4 (10 e^-10 t) di/dt = 84 at ...

**Math**

1cm /50 in = 4 cm/x in x = 200 in

**Math**

It is not a proportion. It is a fraction. divide 144 by 1200 get .12 to convert a fraction to a percent, multiply by 100 100 * .12 = 12 %

**Math**

12/8 = 3/2 = boys/girls boys/total = 3/5 girls/total = 2/5 so that boys/girls = 3/2 so girls /total = 2/5 = girls/400 girls = 800/5 = 160

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