Friday

October 28, 2016
Total # Posts: 27,589

**Probability and statistic**

http://davidmlane.com/hyperstat/z_table.html

*June 27, 2016*

**physics**

60,000 /3600 = 16.7 m/s 45,000 /3600 = 12.5 m/s v =Vi + a t 12.5 = 16.7 + 10 a a = -0.42 meters/second^2

*June 27, 2016*

**physics**

d = (1/2) a t^2

*June 27, 2016*

**Math**

in the slope/intercept form: y = m x + b m is the slope b is the y axis intercept where x = 0 here the slope is positive 0.5 so the line goes up to the right from the point (0,-2) (and of course down to the left :)

*June 27, 2016*

**Math**

y = 35 + 15 x

*June 27, 2016*

**maths**

(x-3)(3x+2)=0 alpha = 3 beta = -2/3 so (x-9)(x-4/9) = y x^2 -9x -4x/9 + 4 = y y = x^2 - (85/9) x + 4

*June 27, 2016*

**English**

One says "at". I suppose if you live in a tunnel, you eat "in" it :) However is you say: "What about dinner in my house?", You probably mean instead of in my yard or garage.

*June 26, 2016*

**GEOMETRY**

p(a)+ p (b) - p(a and b) 1,2,3,or 4 out of 6 = 4/6 tail = 1/2 = 3/6 4/6 + 3/6 - 2/6 = 5/6

*June 26, 2016*

**GEOMETRY**

prob of first one blue = 5/16 now we have 15 in the bag prob of white = 5/15 = 1/3 so 5/16 * 1/3 = 5/39

*June 26, 2016*

**GEOMETRY**

Hey, it is time you should be able to do these.

*June 26, 2016*

**GEOMETRY**

A and B could be 6 A and C - impossible B and C - impossible

*June 26, 2016*

**GEOMETRY**

the attempts are independent so (3/7)^3

*June 26, 2016*

**GEOMETRY**

2 out of 15 2/15

*June 26, 2016*

**GEOMETRY**

1/16

*June 26, 2016*

**math**

18,000 * 1.07^18

*June 26, 2016*

**GEOMETRY**

p even = 3/6 = 1/2 p A = 1/3 they are independent so 1/2 * 1/3 = 1/6

*June 26, 2016*

**Math**

cos T * sin T = 1/4 so 2 cos T * sin T = 1/2 so sin 2 T = 1/2 thus 2 T = 30 deg or pi/6 radians T = pi/12 radians or 15 deg now cos * sin must be + so T in quadrant 1 or quadrant 3 so actually T = pi/12 or T = 13pi/12 which is 195 deg pi/12 + 13 pi/12 + (2pi+pi/12) = (1/12 +13...

*June 26, 2016*

**Biology**

http://shenndesigns.weebly.com/my-physical-trait---curly-hair.html half of each assuming no one has only a little curly so 4:4

*June 26, 2016*

**maths**

a b a + b = 9 a = (1/2) b ============================== (1/2) b + b = 9 so (3/2) b = 9 so b = 18/3 which is 6 which means a = 3 and a b is 36

*June 26, 2016*

**math**

3 of anything + 3 of the same thing = 6 of them 6/30 = 1/5

*June 26, 2016*

**Science**

.05 * 90 = 4.5 mL

*June 26, 2016*

**math - incomplete problem statement**

(L+3)(w+3) = 84 + L w L w + 3 L + 3 w + 9 = 84 + L w 3 L + 3 w = 75 need another piece of information to solve Suspect you were given how much longer it was than wide

*June 25, 2016*

**Physics**

time t at 80 time t at 40 80 t + 40 t = 60 120 t = 60 t = (1/2) hour at each speed distance = 80(1/2) + 40(1/2) = 60km av speed = 60 km/1 hour

*June 25, 2016*

**physics**

north = 400 - 400 = 0 west = 300 d = sqrt (0^2 + 300^2) = 300 I have a hunch you have a typo.

*June 25, 2016*

**Physics**

capacitance is charge per unit voltage 60/40=1.5 Farads

*June 25, 2016*

**Maths Year 10**

x = k - 5 k x = k(k-5) = k^2 - 5k

*June 25, 2016*

**math**

54 = 15 + 3.25 x

*June 25, 2016*

**Science**

Will all that NaCl dissolve? I suspect not.

*June 25, 2016*

**math**

12 - 3 = 9 21 - 12 = 9 hmmm x - 21 = 9 maybe or x = 30 etc

*June 25, 2016*

**Mathematics**

a - (2/5)a = 24 3a/5 = 24 a/5 = 8 a = 40 yes

*June 25, 2016*

**CHEMISTRY**

NO-3 ? , SO2-4 ?, PO3 -4 Where did you get these strange charges for the ions? eg PO3 normally -3 ASSUMING your strange valences: In +3 NO -3 then to be neutral InNO In+3 * 4 = +12 SO2-4 * 3 = -12 so In4(SO2)3 similarly In4 (PO3)4 But I suspect you have the original statement ...

*June 24, 2016*

**trig**

north = -3*14+2*14*cos 60 east = 2*14*sin 60 d^2 = north^2 + east^2

*June 24, 2016*

**Math: PreCal**

yes, amplitude is five and period is 3 pi when x = 0: y = 5 cos (-pi/6) = 5 (.866) that is not a max or a min or and x intercept However there is always a reflection about the points where the argument of the cos function is zero because cos -z = cos z that is when (4/6)x = pi...

*June 24, 2016*

**physics**

some point (0,y) on y axis between y = -3 and y = +6 field up = k(-12)/(6-y)^2 field down = k(-5)/(y-3)^2 so 12(y-3)^2 = 5(6-y)^2

*June 22, 2016*

**physics**

find the linear velocity of the car from v = a t then angular velocity = v/R

*June 21, 2016*

**maths**

Ah, there, on a new computer that would not let me post link unless I typed my Jiska name in :)

*June 21, 2016*

**maths**

http://www.mathsisfun.com/numbers/dividing-by-zero.html

*June 21, 2016*

**English**

4-1 and 4-2 are correct although 4-2 is unlikely. 4. and 4-3 are incorrect.

*June 21, 2016*

**whoops, forgot what I did before**

I mean a = (F/m)e^-(bt/m)

*June 19, 2016*

**physic mechanic**

Friction force, unlike gravitational or electrostatic is not directed toward a source like a center of mass or a charge. Friction is therefore not a central force. Did you get your earlier one about a = F/m (1- e^(bt/m) ) alright?

*June 19, 2016*

**algebra**

each year value = 0.92 value year before v = Vi (0.92)^n v = 25,000 (0.92)^6

*June 19, 2016*

**Scient**

a mL of water is a gram 4.5 / x = .09 x = 50 grams water remains so 450 grams evaporated

*June 18, 2016*

**Physics**

7 m * 2 v = 14 m v (1/2)(7m)(2v)^2 = (1/2)(7)(4) mv^2 = 28 * (1/2)m v^2

*June 18, 2016*

**Physics (Normal force and static coefficient)**

F down slope = m g sin 42 = 2 * 9.8 * sin 42 = 13.1 Newtons down the slope so 13.1 = mu m g cos 42 or sin 42 = mu cos 42 mu = tan 42 mu = 0.900 At least 0.900 could be more

*June 18, 2016*

**Maths**

J = A - 15 J+10 = (1/2)(A+10) A - 15 + 10 = A/2 + 5 A/2 = 10 A = 20 J = 5 ========== check 2(5+10) = 20+10 30 = 30 sure enough

*June 18, 2016*

**Math**

In quad 2 sin is + cos is - of course we can look up the angle knowing the tangent and then find the sin etc but that is too easy. tan T = -5 = sin T/cos T cos T = sqrt (1 - sin^2 T) so -5 = sin T / sqrt(1-sin^2 T) 25 (1-sin^2 T ) = sin^2 T 25 = 26 sin^2 T sin^2 T = 25/26 sin ...

*June 17, 2016*

**Geo Quiz**

No way you could help the guy below you, Momen, who asked a far more difficult question luckily answered by Bob Pursley elsewhere.

*June 17, 2016*

**Geo Quiz**

All of your choices are nonsense the way you typed them without parentheses (x+3)^2 + (y-6)^2 = 25

*June 17, 2016*

**Geo Final**

surface area is 6 times area of one face = 6 (9) = 54

*June 17, 2016*

**social studies.**

You do not need help. You are doing just fine. For number four I might say the poor unemployed people of the country rather than the Republic itself.

*June 17, 2016*

**Calculus**

If you use right endpoints for the height of each rectangle, Bob has it I think and the answer would be 8. If you use trapezoids you get a more accurate answer, 9 , but they asked for the inaccurate answer.

*June 17, 2016*

**CALCULUS**

well, try this backwards assuming you answered correctly y = -4 cos [ ln(6x) ] dy/dx = -4 (-sin [ln(6x)]*6/6x = 4 sin [ln(6x)] / x I see nothing wrong with your answer.

*June 16, 2016*

**geometry**

(x+3) / (3x-1) = 1/2 2 x + 6 = 3 x - 1 x = 7 GR = 3(7) - 1 = 20

*June 16, 2016*

**Math**

subtract 3 t from both sides 2 c = 35 - 3 t divide both sides by 2 c = (35/2) - (3/2) t or c = 17.5 - 1.5 t

*June 14, 2016*

**Math**

well, they all amount to the same thing. add -2 x + 5 to both sides 4 x - 2 x = 9 + 5 2 x = 14 x = 7

*June 14, 2016*

**physics**

I believe that is indeed Dr WLS ! To be sure, how did we get to Nova Scotia and back ?

*June 14, 2016*

**physics**

W = k/r^2 dW/dr = -2kr/r^4 dW = - 2 k dr /r^3 ==================== 532 N = k / 3959^2 so k = 532 (3959)^2 so dW=-2 * [532 * 3959^2]* 1/3959^3 dW = -.2687

*June 14, 2016*

**physics**

That is called "extrapolation". The answer is of course "maybe" :)

*June 14, 2016*

**History**

Basically two different political viewpoints but see: http://www.thecanadianencyclopedia.ca/en/article/bomarc-missile-crisis/

*June 11, 2016*

**Two different people misspell the same way?Physiscs**

If same height at both ends, symmetric parabolic path. Goes 100 yards? I guess I use obsolete units, 300 feet and g = 32 ft/s^2 Vi = V sin 80 = .984 V u = V cos 80 = .174 V 300 feet = u t 300 = .174 V t how long does it take? h = Vi t - 16 t^2 h = 0 at start and finish 16 t^2...

*June 11, 2016*

**Science**

Water power is cheaper than coal power. Although building the dam is expensive, the water is considered free there from then on ( I could argue at length about that, being into eating salmon for example but anyway....). Coal must be dug up, oil must be pumped up, gas must be ...

*June 11, 2016*

**Science**

For years, every spring, I counted alewives going up a silly concrete fish ladder around a dam here. I always had the early morning shift and there was one doe who often came out of the woods behind to look over my shoulder at my clipboard. If I moved an eyelash she would ...

*June 11, 2016*

**Science**

They may be invasive from the Atlantic via the canal but they seem to love them on Lake Michigan: http://www.jsonline.com/news/wisconsin/alewife-crash-on-lake-michigan-raises-concerns-for-salmon-fishing-b99592228z1-331900031.html (salmon fishing on lake Michigan ?)

*June 11, 2016*

**Science**

Please just send them here. We work like crazy to let them spawn, then they mix with the full time ocean varieties of herring at sea and get swept up by the pair trawlers. I wonder how they survive in the lakes. They must have adapted to full time fresh water.

*June 11, 2016*

**Science**

The reference also does not mention that instead of a fast running stream with its fast running fish, you now have a completely different ecosystem upstream as well. You have a pond or lake now, and any silt in the flow upstream will settle to the bottom in the still water. ...

*June 11, 2016*

**Science**

I am also into alewives and eels and shad, even sturgeon. Needless to say we fish around here and in fact just finished tearing a dam out here so the fish could get upstream from the ocean to spawn.

*June 11, 2016*

**Science**

.... and those salmon that I always worry about?

*June 11, 2016*

**Physics**

I guess we assume the temp is uniform over the surface as is the incoming power (obviously untrue) 5.67*10^-8 T^4 = 1700 T^4 = 300 * 10^8 T = 4.16 * 10^2 = 416 K 416 - 273 = 143 C Hotter than boiling water. Habitable?

*June 11, 2016*

**Chemistry**

Think table salt, NaCl The Na has given up an electron to the Cl so the Na end of the molecule is charged + while the Cl end of the molecule is charged -. The molecule is "polar". That gives a good grip to the next molecule whose - side sidles up to our + side and ...

*June 10, 2016*

**science**

the mass, density and volume are assumed not to change R is old radius Rn is new radius V = pi R^2 L Vn = pi Rn^2 (1.25) L so 1.25 Rn^2 = R^2 resistance = k *Length/area new area = old are /1.25 new length = old length*1.25 so new redistance = old resistance *1.25/(1/1.25) or ...

*June 10, 2016*

**physics beats me**

no change in momentum on system means no net force on system. Force on left charge same as on right charge but opposite direction so total on system is zero. Horizontal electrical force on each Fe= k Q1 Q2 / d^2 let x = d/2 = distance from center line sin 15 = x/.65 x = .168 ...

*June 9, 2016*

**Math**

Although the easy formula for the area is A = (1/2)b h that does not help much if you do not know the altitude h Use Heron's formula http://www.mathopenref.com/heronsformula.html

*June 9, 2016*

**ok but do not believe you**

(1/7)(8/9) = 8/63 However no way the large takes 7 times as much milk as the medium. You have a typo or something.

*June 9, 2016*

**Algebra**

I get 32% of students with grades of 13.7 or above. try: http://davidmlane.com/hyperstat/z_table.html

*June 9, 2016*

**Physics**

R = 400 meters v = 130,000/3600 = 36.1 m/s Ac = v^2/R = 3.26 m/s^2 Ac/g = mu = 3.26/9.81 = .322

*June 9, 2016*

**math**

P V = n R T p, n and R constant so V1/T1 = V2/T2 T1 = 60 + 273 = 333 deg Kelvin 2 / 333 = 3 / T2 T2 = 999/2 = 500 K 500-273 = 227 deg C

*June 9, 2016*

**geometry**

m = slope = (13-5) / (-6 - 2) = 8/-8 = -1 y = -1 x + b 1 = -1(-3) +b b = -2 so y = -x -2

*June 9, 2016*

**Calc**

cos x dx + x^2 dy + 2 x y dx = 0 x^2 dy = - (cos x +2 xy)dx dy/dx = - (cos x + 2 x y)/x^2

*June 8, 2016*

**MATH**

hypotenuse

*June 5, 2016*

**math**

hypotenuse = sqrt(a^2+b^2)

*June 5, 2016*

**Math**

19 = (1/3) 45 ? try again f = b + 26 yes b+3 = (1/3)(f+3) this was wrong 3 b + 9 = f+3 3 b - f = -6 3b -b - 26 = -6 2 b = 20 b = 10 f = 36 ======================== now 13 = (1/3)(39) yes

*June 5, 2016*

**maths-need help**

the two vectors are the same length, call it 1 Draw coordinate system with a from origin to x = 1 along x axis Now draw b, length = 1, from origin to lower right in quadrant 4 Now complete parallelogram to find a+b and a-b vectors see that for a-b to be length of 1, need ...

*June 5, 2016*

**Collins - dangerous**

Collins, please check your answers.

*June 5, 2016*

**Math**

d/15 - d/20 = 8/60 4 d - 3 d = 8 d = 8 ===================== then Amy takes (8/20)*60 =24 min and Ashley takes (8/15)*60 =32min Indeed difference of 8 min

*June 5, 2016*

**physics**

.72 meters = (1/4) wavelength but wavelength = c T = c/f so 4(.72) = 336/f f = 336/2.88 f = 117 Hz see: http://www.physicsclassroom.com/class/sound/Lesson-5/Closed-End-Air-Columns

*June 4, 2016*

**physics**

50 = Vi t + .5 a t^2 v = Vi + a t = 0 at end so a = -Vi/t = -20/t 50 = 20 t - .5 (20/t)t^2 50 = 20 t - 10 t = 10 t t = 5 seconds a =-20/5 = -4 meters/second^2

*June 4, 2016*

**Physics**

u = 39 cos T 39 = u t = 39 cos T * t t = 1/cosT total time in air rise time = t/2 = 1/(2cosT) vertical problem 0 = 39 sin T - g * 1/(2 cos T) but g/2 = 4.9 m/s^2 4.9/cos T = 39 sin T cos T sin T = 4.9/39 2 sin T cos T = 9.8/39 so sin 2T = .251 2T = 15.55 T = 7.28 degrees

*June 4, 2016*

**Hey**

I did the arrow one, now you do some.

*June 4, 2016*

**PHYSICS**

C = charge/unit voltage 5*10^-6 = Q/V For one volt, capacitor holds 5*10^-6 coulombs of charge

*June 4, 2016*

**physics**

What angle? What is density of fluid?

*June 4, 2016*

**physics**

volume = area of base * height V = pi r^2 h but r = D/2 V = pi (D^2/4) h = (pi/4) D^2 h

*June 4, 2016*

**Science**

By the way human passengers are, about the lowest density cargo you can imagine. They want huge amounts of space for their mass and are usually in a hurry. Therefore they are not ideal ship cargo and passenger ships have huge volumes above water for limited draft and ...

*June 4, 2016*

**Science**

The mass of the ship and cargo are supported by the displacement of water (Archimedes Principle) whereas an aircraft (unless a balloon) is supported by lift which requires power from the engines. Therefore you can move huge masses with a ship that you could never lift into the...

*June 4, 2016*

**Social Studies (Please check these)**

a :)

*June 4, 2016*

**Physics**

No external forces on system so center of mass continues at constant speed of zero so does not move how far did he walk in the canoe? 4.00 - 1.5 = 2.5 m distance he moved * his mass = distance canoe moved * its mass 2.5 *71.9 = 95 x x = 2.5 * 71.9 / 95

*June 4, 2016*

**Math**

boat 1 north 45 cos 70 east -45 sin 70 boat 2 north -57 cos 23 opposite so add east 57 sin 23 opposite so add total north = 15.4 + 52.5 = 67.9 total east = +42.3 + 22.3 = 64.6 total =sqrt(67.9^2+64.6^2)

*June 4, 2016*

**Social Studies (Please read this)**

Post it as a separate question.

*June 4, 2016*

**typo**

The Voting Rights Act attempted to abolish discrimination in voting. The act abolished mandatory literacy tests and other requirements intended to prevent black people from voting. An effect of this act was a tremendous increase in number of minority voters. In 1968, blacks ...

*June 4, 2016*

**Social Studies (Please read this)**

One important right that we have in South Carolina is religious freedom. Another right we have in this state is the right to vote. These rights mean that we allowed these things no matter what. People cannot force a religion on to a person or not allow another to vote. Along ...

*June 4, 2016*

**Social Studies (Please read this)**

The Voting Rights Act attempted to abolish abolish discrimination in voting. The act abolished mandatory literacy tests and other requirements intended to prevent black people from voting. An effect of this act was a tremendous increase in number of minority voters. In 1968, ...

*June 4, 2016*