Thursday

August 25, 2016
Total # Posts: 26,783

**physics**

when 4 t = 2 pi we have gone around the circle from t = 0 so 4 T = 2 pi T = 2 pi / 4 = pi/2
*February 28, 2016*

**Chemistry**

http://www.youtube.com/watch?v=MKLi-V0CY9M
*February 27, 2016*

**Math**

2(x-4)+y=6 3x-2(y-3)=13 2 x - 8 + y = 6 3 x - 2 y + 6 = 13 2 x + y = 14 3 x -2y = 7 y = 14 - 2x use that 3 x - 2 (14-2x) = 7 3 x - 28 + 4 x = 7 7 x = 35 = 7*5 so x = 5 go back and find y
*February 27, 2016*

**Math**

y= -3/2x-1 which I assume means y = -(3/2)x - 1 so use that 2 [ -(3/2)x - 1 ] - x = -10 -3 x - 2 - x = -10 -4 x = -8 x = 2 etc
*February 27, 2016*

**Physics**

well, you have a + 80 e charge fired at a +1 e charge they repel each other How close will the proton get to the 80 protons? when the kinetic energy of the oncoming proton is used up climbing the potential hill of the 80 protons. it stops and backs away Ke = (1/2) m v^2 ...
*February 27, 2016*

**physics**

No conduction or convection through vacuum, only radiation (use shiny material to reflect)
*February 27, 2016*

**physics**

i = 25/Requivalent = 1 amp so we need Req = 25 In parallel Req = R1R2/(R1+R2) 25 = 50 R2/(50+R2) 25 (50 + R2) = 50 R2 50 + R2 = 2 R2 R2 = 50 which we could have guessed :)
*February 27, 2016*

**PHYSICS**

So where are your answers?
*February 27, 2016*

**MATH**

there are 3 ft per yard there are 9 ft^2 per yard^2 w = (20/3) yards so (20/3) L = 396 L = 3 * 396 / 20 yards multiply by 3 if you want feet
*February 27, 2016*

**Physics**

i = V/R = 12 / .004 amps P = i V = 144/R Joules i = 80 R = V/i = 12/ 80 external resistance Rx = R - .004 power to motor = i^2 Rx = 6400 Rx
*February 27, 2016*

**Figures missing**

Probably F * 49.6 = 1460 * 1.90 but I do not see a figure
*February 26, 2016*

**science**

100 = (1/2) a t^2 so 200 = a (25) a = 8 m/s^2 F = m a = (200/9.81) 8 F = 163 N That is a pretty light bike if it has a rider, perhaps a small child.
*February 26, 2016*

**Stats please help**

5/6 * 5/6 * 5/6 * 5/6 = answer = (5/6)^4 = .482
*February 25, 2016*

**MATH**

yes, although you sure use a lot more steps than I :) -4+1 = -3 -3*4 = -12
*February 25, 2016*

**history**

Now I may explode being from Massachusetts so I think you better Goggle them.
*February 25, 2016*

**Check math please!**

Yes, both right
*February 25, 2016*

**Check math please!**

second one same method 5/9 yes consonant =2/3 so not is 4/9 agree - note I used opposite approach from you, same answers :)
*February 25, 2016*

**Check math please!**

Anna mixes the letters S, E, L, E, C, T, E, and D thoroughly. Without looking, Mary draws one letter. Expressed as a fraction, decimal, and percentage, what is the probability that E will NOT be the letter Mary selects? A. 3/8, 0.375, 37.5% B. 8/5, 1.6, 16% C. 5/8, 0.625, 62.5...
*February 25, 2016*

**we do not have your drawing**

so we do not have the directions of 1 and 2 we know that the total east (x) momentum must be zero and the total north (y) momentum must be zero
*February 25, 2016*

**Math**

8.6 cm ( 50 mi/2 cm) = 215 mi
*February 25, 2016*

**Math**

.15 * 8.25 about .8 + .4 = 1.2
*February 25, 2016*

**Math**

5 * .06 * 2000 = 600 so yes and see you can check it easily :)
*February 25, 2016*

**science help PLS**

I would bet on b but around here the problem is sea gulls
*February 25, 2016*

**Math**

yes, did that a while ago
*February 25, 2016*

**physics**

lets do adolph (1/2) m v^2 = m g h v^2 = 2 g h = 2 (9.81)(.56) so v = 3.31 m/s at push so adolph momentum = 104*3.31 = 345 kg m/s Ed has the same magnitude of momentum 80 V = 345 Ved = 4.31 m/s 4.31^2 = 2 (9.81) (h) h = .9464 m
*February 25, 2016*

**Mathematics**

find slope of tangent dy/dx 2 x + 2 y dy/dx - 2 -4 dy/dx = 0 dy/dx (2y-4) = 4 - 2x dy/dx = (4-2x)/(2y-4) at x = 5 and y = -1 dy/dx = (4 -10)/(-6) = -6/-6 = 1 :) slope of normal = -1/slope = -1 so y = -x + b -1 = -5 + b b = 4 so in the end y = -x + 4
*February 25, 2016*

**Math**

(z - 2 +3i)(z -2 -3i) = 0 commutative property to multiply z (z -2 -3i) = z^2 -2 z -3 z i -2(z -2 -3i) = -2 z + 4 + 6 i 3i(z -2 -3i) = +3zi -6 i + 9 add ------------------------------ = z^2 - 4 z + 13 so a = -4 and b = 9
*February 25, 2016*

**Math**

matrix for reflection over y axis: -1 +0 +0 +1 dilation matrix r r or r r matrix multiplication is not necessarily comutative dilate first r r * x y = r x, r y then reflect rx , ry * -1 +0 +0 +1 = -rx , ry now reflect first -1 +0 |x| +0 +1 |y| = -x , + y now dilate -rx , + r y...
*February 25, 2016*

**linear programming**

c = acres of corn w = acres of wheat constraints: c+w </= 100 graph that line,shade under wheat cost = 20 w corn cost = 40 c 20 w + 40 c </= 2400 graph that line, shade under wheat labor = 4 w corn labor = 16 c 4 w + 16 c </= 800 graph that line, shade under Now the ...
*February 25, 2016*

**Maths**

3 y^2 dy/dx - dy/dx / y^2 = 2 x -7 dy/dx dy/dx (3 y^2 -1/y^2 + 7) = 2 x dy/dx = 2 x /[ 3 y^2 -y^-2 + 7 ]
*February 25, 2016*

**physics**

net north = 8 - 2 = 6 Newtons net east = 6-4 = 2 Newtons |F| = sqrt (36 + 4) = 2 sqrt 10 tan angle n of e = 6/2 = 3 angle n of e = 71.6 degrees north of east or 90 - 71.6 = 18.4 degrees east of north (compass direction)
*February 25, 2016*

**Physics**

mechanical advantage = 13.4/1.34 = 10 weight = 53.4 g = 53.4*9.81 divide by 10 for input force 5.34 * 9.81 = 52.4 Newtons input
*February 25, 2016*

**Physics**

Work = force * distance = 13.4 *30 = 402 Joules (1/2) m v^2 = 402 1.524 v^2 = 804 v = 22.9 m/s
*February 25, 2016*

**MATH PLEASE**

x(5.49) = (5.49 - 2.25) x = .59 59 %
*February 25, 2016*

**MATH PLEASE**

1.4 * 12.95 = 18.13
*February 25, 2016*

**MATH PLEASE**

.52 s = s - 38.87 38.87 = .48 s s = 80.98
*February 25, 2016*

**Chemistry**

N2H4 + N2O2 = 2H2O + 2 N2 limited by .3 mol N2H4 so get .6 mol N2
*February 25, 2016*

**History**

agree, see: http://www.ourdocuments.gov/doc.php?flash=true&doc=21
*February 25, 2016*

**Pre Cal**

assume you mean x^2 + y^2 = 0 That is a circle of zero radius with center at the origin :) In other words a dot at the origin.
*February 25, 2016*

**Science**

Looks like it reacted chemically with something in the air to me :)
*February 25, 2016*

**math**

first one black = 26/52 = 1/2 second one black = 25/51 third one black = 24/50 fourth one black = 23/49 etc until we get to number 12 then multiply all those fractions that means you got every king, queen and jack 4 kings + 4 queens + 4 jacks = 12 of the 52 card 1 = 12/52 ...
*February 25, 2016*

**MATH**

3 x - y = 4 3 x - y = 6 never cross -parallel, no solution 2 x - y = 1 3 x + y = 6 --------------add 5 x = 7 x = 7/5 etc 1 x - 5 y = 5 3 x + 1 y = 7 multiply first by 3 3 x -15 y = 15 3 x + 1 y = 7 ---------------subtract -16 y = 8 y = -1/2 etc
*February 24, 2016*

**Math**

21 * 7 = (1 - 5/8) p = (3/8) p p = 49*8 = 382 pages
*February 24, 2016*

**Algebra**

y = - x^3 no y = -3^x would be but not this
*February 24, 2016*

**Algebra: Check Answer**

LOL no need to ask, plug back in h = -16(10.4)^2 + 156(10.4) +105 = -1730.56 + 1622.4 + 105 = -1730.56 + 1727.4 close enough to the ground :)
*February 24, 2016*

**Math**

Yes dA/dr = 2 pi r = 6.28 r correct however think a little more dA = 2 pi r dr = circumference * dr If you draw a picture of a circle r and then one outside it with radius r + dr You will see immediately that the change in area is the strip of length 2 pi r times the width dr
*February 24, 2016*

**Math**

dA = 2 pi r dr yes, correct however notice that this is simply the circumference the new area added is the circumference * dr
*February 24, 2016*

**math**

Yes we agree but I simplified
*February 24, 2016*

**math**

I assume dy/dx=(4sqrt(y)ln x)/x y^-.5 dy = 4 (ln x /x)dx y^.5 = 2 [ .5 ln^2 x ] y^.5 = ln^2 x y = ln^4 x + c
*February 24, 2016*

**Physics**

bullet momentum = .017 v total mass = .017+1.2 = 1.217 kg final momentum = initial momentum .017 v = 1.217 V' V' = .014 v normal force on table = m g = 1.217 (9.81) friction force = .23*1.217*9.81 = 2.75 Newtons work done = 2.75 *8.6 = 23.6 Joules so 23.6 =(1/2)mV'...
*February 24, 2016*

**Algebra 2**

yes all 3 are correct but it is easier to use sin and cos sin^-1 (3/19) and cos^-1 (18.8/19)
*February 24, 2016*

**ALGEBRA**

surface area = area of top + area of bottom + area of side = pi r^2 + pi r^2 + 2 pi r h = 2 pi (r^2+ r h) = 2 pi r (r + h) = 2 *pi*4 * 10 = 80 pi volume = pi r^2 h = pi *14 * 6 = 84 pi
*February 24, 2016*

**Math**

let z = y^.5 then dz = .5 y^-.5 dy dy = 2 y^.5 dz = 2 z dz 2 z dz /(z cos^2 (z) ) = x dx dz/( cos^2 (z)) = .5 x dx tan z = .25 x^2 + constant tan y^.5 = .25 x^2 + constant
*February 24, 2016*

**Mensuration**

Now I showed you how to do one by subtracting rectangles. You do this one.
*February 24, 2016*

**Math**

That is quite a markup : I have a sneaking suspicion that they mean 140% markup but will do it as stated .75 * price = 39.95 so usual price = 53.27 cost + 2.40 * cost = 53.27 3.40 * cost = 53.27 cost = 15.67 39.95 - 15.67 = 24.28
*February 24, 2016*

**Trigonometry**

m and j tan 30 = m/15 tan 45 = 1 = j/15 j - 15 and m = 15 tan 30 = 8.66 m+j = 23.7
*February 24, 2016*

**Precalculus**

sec 4x = 1/cos 4x I can not graph it for you here but note that cos 90 or pi/2 = 0 so you are going to have a bunch of vertical asymptotes
*February 24, 2016*

**Mensuration**

the original sheet is 30*20 = 600 cm^2 the remaining sheet is 30-8 by 20-8 or 22 * 12 = 264 cm^2 so you removed: 600 - 264
*February 24, 2016*

**Calculus**

pi/3 = 60 degree just so I do not have to use radians on my calculator :) c^2 = a^2 + b^2 - 2 a b cos C get initial stuff first cos 60 = 1/2 sin 60 = .866 c^2 = 64 + 169 - 208 cos 60 c^2 = 233 - 104 = 129 c = 11.4 now do the problem 2 c dc/dt = -208 (-sin 60) dC/dt so dc/dt = ...
*February 24, 2016*

**Math**

i = -75 p^2 + 600 p if p = 3 i = -75 (9) + 1800 1,125 = -75 p^2 + 600 p 75 p^2 -600 p + 1,125 = 0 solve quadratic for 2 values of p. Throw out any negative one etc for max I assume you do not know calculus so complete square to find vertex 75 p^2 - 600 p = -i p^2 - 8 p = -i/75...
*February 24, 2016*

**statistics**

I will do three cards, you do five. 52 cards, 26 are red so find probability of all black first draw 26/52 = 1/2 second draw 25/51 third draw 24/50 = 12/25 prob of all black =.5*25/51*12/25 =.118 so 1-.118 = .882 for at least one red in three draws
*February 24, 2016*

**physics- check this out**

v = Vi + a t v = 0 at stop a = -Vi/t = -35 m/s^2
*February 24, 2016*

**Physics**

7 t = d 13 t = d+42 so 6 t = 42 t = 7 7 t = d = 49
*February 24, 2016*

**physics**

A kilowatt is 1,000 Watts
*February 24, 2016*

**Physics**

I will have to guess at your drawing. Both objects fall the same. The first one keeps its horizontal velocity so both fall 1.14 meters v = g t = 9.81 t 1.14 = (1/2) g t^2 = 4.9 t^2 so t = 0.482 second fall time for both so vertical velocity of both is 9.81 * .482 = 4.73 m/s ...
*February 24, 2016*

**physic**

falls 63 m 63 = 4.9 t^2 calculate t which is time in air now range = 20 t the end.
*February 24, 2016*

**physics**

Kilo
*February 24, 2016*

**physics**

22.61 g/cm^3 * (100 cm/m)^3 (1kg/1000g) = 22,610 kg/m^3 by the way water is about 1000 kg/m^2
*February 24, 2016*

**????**

You forgot the equation
*February 24, 2016*

**physics**

20 east
*February 24, 2016*

**physics**

I assume you mean 8 hours. Velocity is the displacement /time and direction Here that is 320/8 or 40 mph North The 400 zigging and zagging is irrelevant for velocity but important if you wanted speed instead of velocity
*February 24, 2016*

**please help**

Please just do what I suggested. Goggle Mt Kilimanjaro and those countries.
*February 24, 2016*

**African climates - where to start?**

I do not know what to say. Except for one mountain (http://www.tanzaniaparks.com/kili.html) there is not much snow. However everything else is there :) Desert in the North, riverine in the Nile valley, jungle in the center and down the Congo river. Savannas, farmland, grazing ...
*February 24, 2016*

**science**

when the potential (voltage) is different in different places on the conductor.
*February 21, 2016*

**Science**

It doubles every (1/4) day? in 7 days it doubles 28 times 2^28 = 268,435,456
*February 21, 2016*

**Science**

Maybe you mean Bernoulli : (1/2)rho v^2 + rho g h + p = constant If flow is constant in time and no frictional losses rho = density h = altitude p = pressure g - gravitation acceleration v = speed
*February 21, 2016*

**Physics**

I can not sketch it for you. v = (2t+1.34) i + 3.34 j + (6t^2 - 8t) k so put in t = 2 a = 2 i + (12t-8) k again use 2 for t
*February 21, 2016*

**Physics**

A: v = 10 pi/(10.34) Ac = v^2/r = 20 pi^2/(10.34)^2 B: v = 20 pi/(10.34) Ac = 40 pi^2/(10.34)^2
*February 21, 2016*

**Maths**

(-4/3) x = 16/3 -4 x = 16 x = -4
*February 21, 2016*

**science**

60min/hr * 60 sec/min = 3600 seconds/hour 2 * 3600 + 35 = 7235
*February 21, 2016*

**Chemistry**

we are close to STP here where one mol is 22.4 liters 58.4/22.4 is around 2.61 moles 10.3/2.61 = 3.95 grams/mol Helium maybe ?
*February 21, 2016*

**Algebra**

Oh well, I'll play 300 = k * 3^2 * 10.62 so k = 300/(9*10.62) = 3.14 remarkable :) in fact v = pi r^2 h = pi * 3^2 * 10.62 = 300.27 :) so we say v = 3.14 * r^2 *h = 3.14 * 16 * 15.92 =785 cm^3
*February 20, 2016*

**Physics**

horizontal rope force= 100 cos 60 = 50 N so a) work done by tension = 50*15 = 750 Joules b) NONE !!!! there is no vertical displacement !
*February 20, 2016*

**Math**

.6 (299) = 179.4
*February 20, 2016*

**math**

I guess you mean circumference of a circle of radius 5.5 in if so 2 pi r = 11 pi
*February 20, 2016*

**High school calculus**

I have a extra b in there.
*February 20, 2016*

**High school calculus**

dy = (bx+5)^-3 dx let z = bx+5 then dz = b dx and dx = (1/b) dz dy = (1/b) z^-3 dz y = (1/b)(-1/2)z^-2 + c y = -1/(2b z^2) + c but z^2 = b^2x^2 + 10 bx + 25 so 2 b z^2 = 2b^3x^2 + 20 b^2 x + 50 b so y = -1/(2b^3x^2 + 20 b^2 x + 50 b) + c
*February 20, 2016*

**Algebra**

t = k r^2/z^3 4 = k 36/27 k = 3 so t = 3 r^2/z^3 ============================ c = k d^2/L .54 mho = k 3^2/50 k = 50 * .54 /9 = 3 again LOL (note - in your units which are not the ones a physicist would tend to use)
*February 20, 2016*

**math**

Some blame it on people like Pythagoras but I think folks along the Indus River thought it up to keep track of monsoons and crops and water level and stars and stuff. The really important guy was Sicilian but everyone calls him Greek named Archimedes. He not only figured out ...
*February 20, 2016*

**phy 231**

centripetal acceleration Ac = v^2/r = r omega^2 omega is part a r = radius there = Re sin 49 [ note - usually we use latitude which is angle North of the equator in this case cos(90-49)]
*February 20, 2016*

**physics**

(1/2) a t^2 = h (1/2)(9.81)(36) = h in meters
*February 20, 2016*

**math**

I can guess based on the possible answers. The only one with a y axis intercept is y = 5 x + 2 that is $2 to walk in the store and a unit rate of $5 per sandwich
*February 19, 2016*

**Statistics**

You are welcome.
*February 19, 2016*

**Statistics**

http://davidmlane.com/hyperstat/z_table.html
*February 19, 2016*

**Math**

http://www.jiskha.com/display.cgi?id=1455913440
*February 19, 2016*

**Just did it**

see below
*February 19, 2016*

**Math**

.80 * .75 * 179.99
*February 19, 2016*

**physics**

work output = 500 * 1.7 = 850 Joules work input = 1000 Joules efficiency = (850/1000)100 = 85 % since you did not say what the velocity ratio was, how would I know what the mechanical advantage was? They are the same on inverses depending of which way you write the velocity ...
*February 19, 2016*

**chemistry**

if they have more than one electron or lack of electrons in complete outer shell they can lose or gain electrons to form complete outer shells. Google oxidation reduction
*February 18, 2016*