Monday

December 5, 2016
Total # Posts: 28,273

**math**

1. yes 2. yes, works for any old y 3. just like 2 4. yes

*November 28, 2016*

**PHYS-041-Keiler: Physical Science**

assuming 5730 year half life a = Ai e^-kt a/Ai = .5 = e^-k(5730) ln .5 = -k(5730) k = 1.21 *10^-4 so a = 22 e^-(1.21*10^-4*11400) = 22 * e^-1.38 = 22* .252 = 5.54 kg

*November 27, 2016*

**physics**

T = 2 pi sqrt(L/g)= (2 pi/sqrt g)L^.5 = 1 second at 22 deg so you can get initial L dT/dL = (2 pi/sqrt g).5 /sqrt L dT/dt = dT/dL * dL/dt so what is dL/dt dL/L = 24*10^-6 dT dL /dT = 24*10^-6 L dL/dt = dL/dT *dT/dt = 24*10^-6 (-.625) L so dT/dt = [(2 pi/sqrt g).5 /sqrt L][24*...

*November 27, 2016*

**Physics**

assume I = (1/2) m r^2 for disk = (1/2)(6.5)(r)^2 Torque = I alpha where alpha = ang acceleration = a/r T = tension in rope so torque = T * r = I (a/r) T = I a/r^2 = (.5 m )a=.5(6.5)a now the block force down = m g force up = T ma = mg - T T = mg-ma = 2.5(g-a) so putting them ...

*November 27, 2016*

**Stoichiometry**

4.5 grams, look below at earlier question

*November 27, 2016*

**Math**

12 marbles to start drew one yellow 4/12 then 11 marbles of which 3 are yellow 3/11 so 4/12 * 3/11 = 1/11

*November 27, 2016*

**maths**

cost = 1040 - 240 = 800 (240/800)100 = 30% profit 12 * 6.50

*November 27, 2016*

**Stoichiometry**

(75/1000).6 = .045 mol CaCO3 = 100 g/mol so 4.5 grams

*November 27, 2016*

**Stoichiometry**

CaCl2 + Na2CO3 ---> CaCO3 +2NaCl one to one in mols of each 75 *.6 = x * .4

*November 27, 2016*

**maths**

2400 * .15 2400 * 1.15 .8*2400 before VAT

*November 27, 2016*

**maths**

0.8 Liters * n = 36 Liters n = 38/0.8 = 45 cans ======================= b makes no sense to me. It is a typo I think.

*November 27, 2016*

**Math**

t/5 = (t-5)10 t = (t-5)50 t = 50 t -250 49 t =250 t = 250/49

*November 27, 2016*

**Probablility**

I assume you never use the same machine twice first cardio = 4/10 = 2/5 second = 3/9 =1/3 third = 2/8 = 1/4 fourth = 1/7 product = 2/5 *1/3*1/4*1/7 = 1/210 now weight first =6/10 = 3/5 second = 5/9 third = 4/8 = 1/2 fourth = 3/7 product = 3/5 * 5/9 * 1/2 * 3/7 =1/14 so 1/210...

*November 27, 2016*

**Algebra**

7-5.375 = 1.625 for left and right margins 1.625 - .3125 = 1.3125 for right margin do the vertical problem the same way

*November 27, 2016*

**Algebra**

75*20 + 95*30 = x * 50

*November 27, 2016*

**Math**

5 * 3/1 = 15

*November 26, 2016*

**pre calculus**

100(-.5 -.866i) - 50 - 50 sqrt3 i

*November 26, 2016*

**pre calculus**

we want r(cos T + i sin T) r = sqrt ((-2)^2 +2^2) =sqrt 8 =2 sqrt2 -2 = r cos T = 2 sqrt 2 cos T cos T =-sqrt 2 / 2 T = 3 pi/4 2 = R sin T = 2 sqrt 2 sin T sin T = sqrt2 /2 T = 3 pi/4 all right so z =2 sqrt 2[cos .75 pi+isin .75 pi]

*November 26, 2016*

**AP Calculus**

well lets think it might be like a hot stone cooling down to some room temperature Tf Google Newton's law of cooling T = Ts +(To-Ts)e^-(k t) To is your original 1900 time Ts is your final time in 2100 or whatever which is the fastest one can ever go k is a constant that ...

*November 26, 2016*

**physics**

Your second method is the right way to go.

*November 26, 2016*

**pre calculus**

I think you probably mean: e^(a+bi) =e^a e^bi = e^a (cosb+isinb) then e^i? = e^(0+i?) =(e^0)(cos pi+isinpi) = 1(-1 + 0) or e^i? = -1

*November 26, 2016*

**7th grade Pre- Algebra**

R/5 - 6 = -1 add 6 to both sides R/5 +0 = 6 - 1 R/5 = 5 now multiply both sides by 5 (R/5)5 = (5)(5) R = 25

*November 26, 2016*

**missing question**

[f(x)-f(a)] /(x-a) = 7 as x-->a is the definition of the derivative f'(a) = 7

*November 26, 2016*

**math**

df/dx = 4 x^2/[x^3 +3] at x = -1 df/dx = 4/[2] = 2 so f(-1+dx) = f(-1) + 2 dx here dx = -.1 so f(-1-.1) = -3 +2(-.1) = -3 -.2 =-3.2

*November 26, 2016*

**Physics**

t is in seconds 40 t = 42(t-120)

*November 26, 2016*

**math**

sin ? = 0 slope = cos ? = -1 f(x) = sin(?) -1(x-?) = -(x-?)

*November 26, 2016*

**science**

global positioning systemhttp://www.safewise.com/blog/10-wearable-safety-gps-devices-kids/ ( of course I use GPS to get around the bleak ocean but that is old stuff:) sampling whale snot with drone http://shop.whale.org/pages/snotbot tidal power generation systems http://...

*November 26, 2016*

**Electronics**

http://www.electronics-tutorials.ws/rc/rc_1.html

*November 25, 2016*

**Math**

s^3 = 512 s = 512^(1/3) calculate s = 8 A = 6 (s^2) = 6 * 64

*November 25, 2016*

**Calculus application of sin function**

v = dh/dt = sin pi t then h = - (1/pi)cos pi t but h = A cos (2 pi t/T) so A = -1/pi pi = 2 pi /T so T = 2 so in the ean h =-(1/pi) cos pit = -(1/pi)cos(2 pi t/2) B) h =-(1/pi) cos pit v = dh/dt = sin pi t a = dv/dt = pi cos pi t C)1/pi D) cos 0 = 1 so at t = 0 , 1 , 2 etc E) ...

*November 25, 2016*

**second graph link not rights**

http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=8d8e2c27bcaa121d6ee0de4b98774bb4&title=Polar%20Graphs&theme=blue&i0=r%3D2(2-sin^2%C9%B5)^%C2%BD%20&i1=0&i2=Pi%2F2&podSelect=&showAssumptions=1&showWarnings=1

*November 25, 2016*

**calculus**

I suspect you mean: r=2(2-sin2?)^½ that makes me nervous that since you do not type exponents you might mean 2-sin^2 ? instead of what your typed. I will assume that first graph it here with sin 2? http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=...

*November 25, 2016*

**Science**

mass = 150/g or about 15 kg but who needs it? x = A sin w t v = Aw cos wt a = -Aw^2 sin wt = -w^2 x ============================= when x = .2 = A sin w t v = 5 = Aw cos w t a = +20=+Aw^2 sin w t = +w^2x =============================== so w^2 x = w^2(.2) = 20 w^2 = 200/2 = 100 ...

*November 24, 2016*

**Maths**

x^2 y = V G = 4x+y = 6 ================== y = 6-4x x^2 (6-4x) = V now do the complete the square thing like I did in your other problem to find the vertex of the parabola

*November 24, 2016*

**Engineering**

4 x = 800 x = 200 feet on a side square ========================= prove that square is max area A = x y P = 2 x + 2 y perimeter so x + y = P/2 A = x (P/2 - x) = -x^2 +P/2 x x^2 - (P/2) x = A find vertex,complete square x^2 - (P/2)x + P^2/16 = -A + P^2/16 (x-P/4)^2 = -(A-P^2/16...

*November 24, 2016*

**math**

s = standards d = deluxe 12 s +18 d = 360 ____divide by 6 s + d = 25 ________multiply by 2 2 s + 3 d = 60 2 s + 2 d = 50 -------------- d = 10 then s = 15

*November 24, 2016*

**Physics**

assume you mean 5 m/s^2 50 *1000/3600 = 13.9 m/s v = 13.9 - 5 t 0 = 13.9 - 5 t t = 13.9/5 average speed during stop = 13.9/2 d = (13.9/2) (13.9/5) or d = Vi t - .5 (5) t^2 d =13.9(13.9/5)-.5 (5) (13.9^2)/5^2 = .5 *13.9^2/5 the same

*November 24, 2016*

**physics**

ub^2 = .25 ua^2 average speed for initial slowing = .5(ua+ub) assume constant a t = .05/.5(ua+ub) = .1/(ua+ub) v = Vi +at ub = ua + a t ub-ua = a (.1)/(ua+ub) .1 a = -(ua^2-ub^2) .1 a = - (.75 ua^2) a = -7.5ua^2 now complete trip 0 = ua + a t t = ua/7.5ua^2 = 1/(7.5ua) d = Vi...

*November 24, 2016*

**Math**

There are lots of different ways. perhaps the easiest to understand uses the distributive property 12 = 10 + 2 13 = 10 + 3 (10 + 2) (10 + 3) = 10 (10+3) + 2 (10+3) = 100 + 30 + 20 + 6 = 100 + 50 + 6 = 156 ========================== You can shorten that by saying 10(13) + 2(13...

*November 24, 2016*

**Physics**

If there is no moment (torque) then there is no change of angular momentum [ I omega = constant] If they are not opposite in direction through the same point, they cause a moment, called a "couple"

*November 24, 2016*

**algebra**

n and 2 n 2 n - n = 20 n = 20 and so answer = 2n = 40

*November 23, 2016*

**Gaussian Elimination Method**

LOL, forgot the old easy stuff :)

*November 23, 2016*

**Gaussian Elimination Method**

to check, put it back in -4(-1) -(-2) = ? yes 6 12(-1) -2(-2) = ? yes -8

*November 23, 2016*

**physics**

m v^2/r horizontal m g down tan theta = mg/(mv^2/R)where theta is angle down from horizontal but cos theta = .7/2.8 so theta = 75.5 deg so tan theta = 3.87 so 3.87 = mg/mv^2/R = 9.81/(v^2/.7) v = 1.33 m/s m v^2/R = .4*1.77/.7 = 1.01 m g = .4*9.81 = 3.92 T^2 = 1.01^2 +3.92^2 T...

*November 23, 2016*

**Math**

9*10^-3 LY (5.88*10^12 mi/LY) = 52.92 * 10^9 mi = 5.292 * 10^10 mi

*November 23, 2016*

**math!**

q = first questions/min 2 q = final que/min t min for first ten 48 - t min for final 11 q t = 10 so t = 10/q q t + 2q(48-t) = 21 10 + 96q - 20 = 21 96 q = 31 q = 31/96 questions/min so twice that = 62/96 to finish ======================== check t = 960/31 = 30.97 min 48-t = 17...

*November 23, 2016*

**Algebra 2**

.75 x + .42 y = .5784 (100) x+y = 100 ============================ .75 x + .42 y = 57.84 .75 x + .75 y = 75 ---------------------- -.33 y = - 17.16 y = 52 x = 48 E

*November 23, 2016*

**Physics**

h f = 14.7 eV lambda = c T = c/f c about 3*10^8 m/s

*November 23, 2016*

**Physiscs**

well the length is L sqrt 13 but who cares? force up from floor = m g = 3g (because wall is smooth none up there) force sideways from wall = F thus force sideways at floor = F toward wall Now moments about center clockwise mg * 2L/2 = m g L counter clockwise F*1.5 L + F*1.5 L...

*November 23, 2016*

**physics**

80 km/hr * 1 hr/3600s * 1000 m/km = 22.2 m/s tan T = v^2/r / g = v^2/gr tan T = 22.2^2/(981) tan T = .502 T = 26 deg 39 min

*November 23, 2016*

**Physics**

rho g h 1000 * 9.81 * 20 = 196,200 Pascals = 1.94 atm gage (over 1 atm) or 2.94 atm absolute

*November 23, 2016*

**Physics**

done already

*November 23, 2016*

**Calculus**

Oh, but I said where x = +/- infinity

*November 23, 2016*

**Calculus**

Oh, yes :)O

*November 23, 2016*

**Calculus**

Oh my, look around x = 0 and x = 1 and x = infinity and x = -infinity http://www.wolframalpha.com/input/?i=plot+1%2F(x(x-1))

*November 23, 2016*

**Math**

a) sin is + in I and II b) cos is - in II so there only c) hard to sketch here from origin up 7 distance 25 x^2 + 7^2 =625 and x is - x^2 = 625 - 49 = 576 x = -24 so point is at (-24,7) cos C = -24/25 tan C = -7/24

*November 23, 2016*

**Math**

cos /sin = -1 = cotan 90 + 45 360 - 45

*November 23, 2016*

**Consider the linear programming problem**

You are welcome.

*November 23, 2016*

**Consider the linear programming problem**

which we could have seen without doing the problem :) The potato seed costs less and the profit is more

*November 23, 2016*

**Consider the linear programming problem**

maximize 150 x + 50 y x + y <=70 20 x + 60 y <= 3000 x>= 0 y>= 0 x+y >=1 to fill in input form only http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=1e692c6f72587b2cbd3e7be018fd8960&title=Linear%20Programming%20Calculator&theme=blue result 10500 at (70,0)

*November 23, 2016*

**Calculus**

f' = 10 - 10/x^2 f" = 0 - 10 [ -2/x^3] = 20/x^3 I do not see anyplace where the curvature passes through zero except at x = +/- infinity

*November 23, 2016*

**Linear Programming to Maximize Profit**

You are welcome.

*November 23, 2016*

**Linear Programming to Maximize Profit**

Oh my heavens I have done so many linear programming problems tonight! s uses 6 plastic d uses 3 plastic so 6 s + 3 d </= 300 s uses 4 metal d uses 8 metal so 4 s + 8 d </= 608 s </=22 maximize 10 s + 2 d I get 332 at (22,56) using http://www.wolframalpha.com/widget/...

*November 23, 2016*

**math**

7x = 1.40 x = .20 2x = 0.40 4x = 0.80 5x = 1.00 7x = 1.40 sum = $3.60

*November 23, 2016*

**simplex method**

For instructions using Simplex with pivots etc see http://en.wikipedia.org/wiki/Simplex_algorithm

*November 23, 2016*

**doing with linear programming **

http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=1e692c6f72587b2cbd3e7be018fd8960&title=Linear%20Programming%20Calculator&theme=blue max = 3220 at (12,50)

*November 23, 2016*

**Calculus**

This is a closed path check first if field is potential in which case integral is zero F = z^2 i + 2xy j + 3y^2k del cross F = 0 ???? nope no way so first line = 3 i + 0 j + 0 k F dot line = Fx *3 = 0*3 = 0 second line in x from 3 to 3 = 0 in y from 0 to 3 = 3 in z from 0 to 1...

*November 23, 2016*

**Calc**

or rather curl F

*November 23, 2016*

**but still think MITx**

:)

*November 23, 2016*

**Calc**

curve is ellipse at z = 11 and 5, y = 0 and x = +/-3 (-3 , 0 , 11) (+3 , 0, 5) at z = 8 , x = 0 and y = +/-3 The normal to that ellipse is in he x z plane and is perpendicular to the line joining(-3, 0 ,11)and (3,0,5) slope of that original line dz/dx = -6/6 = -1 remarkable so...

*November 23, 2016*

**MITx**

Just asking :)

*November 23, 2016*

**Calc**

You doing an MITx subject?

*November 23, 2016*

**Calc**

curl of F over the surface curl is i j k d/dx d/dy d/dz fx fy fz is =(dFz/dy-dFy/dz)i +(dFx/dz-dFz/dx)j +(dFy/dx-dFx/dy)k here Curl F =(ex-9x)i +(y-ey)j +(9z-z)k

*November 23, 2016*

**Calc**

Flux = int over S of F dot [1i - (dz/dx)^2j -(dz/dy)^2k] F dot [i -4x^2 j - 4y^2 k] [xy - 4x^2yz -4y^2xz]dx dy now put in 2 -x^2-y^2 for z and do the integrals from 0 to 1

*November 23, 2016*

**physics**

if boy at 1 meter girl at (4/3) meter

*November 23, 2016*

**physics**

50 N * .2 m = 10 Nm

*November 23, 2016*

**The Graphical Method**

I get 40 of A, 0 of B for profit = 1000 maximize 25 x + 15 y constraints 5x+4y<=300 2x+3y<=108 x>=0 y>=0 x+y>=1 (phony to fill fields)

*November 23, 2016*

**linear programming**

http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=1e692c6f72587b2cbd3e7be018fd8960&title=Linear%20Programming%20Calculator&theme=blue try that while I look at your problem

*November 23, 2016*

**Algebra 2 (Please help Ms. Sue!)**

292 ?

*November 23, 2016*

**Algebra 2 (Please help Ms. Sue!)**

f(x)/(x-a) = f(a) here a = -3 so we need f(-3) f(-3) =(-3)^4-9(-3)^3-5(-3)^2-3(-3)+4 = 81 + 9*27 - 45 +9 + 4 = 81 + 243 - 45 + 9 + 4

*November 23, 2016*

**Linear Programming**

note, to make the program format happy I put in max 180x+60y x+y</=60 20x+10y<=700 x>=0 y>=0 x+y>=1 phony but fills boxes

*November 23, 2016*

**Linear Programming**

a+b<=60 20 a + 10b </= 700 a and b >=0 maximize 180 a + 60 b intersections at 0,60 35,0 10,50 at a = 0, b = 60 180 (0) + 60 *60 = 3600 at a = 10, b = 50 180(10) + 60(50) = 4800 at a = 35, b = 0 180(35) = 6300 so plant 35 acres of a and zero of b. Use the whole $700 ...

*November 23, 2016*

**Linear Programming**

http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=1e692c6f72587b2cbd3e7be018fd8960&title=Linear%20Programming%20Calculator&theme=blue

*November 23, 2016*

**Gaussian Elimination Method**

+5 -4 12 divide by 5 to get 1 -5 +3 +9 +1 -4/5 12/5 multiply by 5 and add -5 +3.0 +9 +1 -4/5 12/5 +0 -1.0 21 multiply by -1 +1 -4/5 12/5 +0 +1.0 -21 so y = -21 now multiply second eqn by 4/5 and add to first +1 -4/5 12/5 +0 +4/5 -84/5 +1 +0 -72/5 +0 +1 -21 x = -72/5, y = -21

*November 23, 2016*

**Physics**

sure, if you use a seesaw, you must be twice as far from the pivot point as the weight is. You must move twice as far down as the weight moves up. (draw geometry) You could use a pulley with one end of the line attached to the ceiling, then running down through the block on ...

*November 23, 2016*

**Calculus**

depth = h dV/dh = area of surface (draw it :) dV/dh = pi r^2 = surface area r = (2.7/4.3)h remember to use chain rule. for example dV/dt = 59.5 m^3/min but dV/dt = dV/dh dh/dt so dh/dt = 59.5/ (pi r^2) etc

*November 23, 2016*

**Science**

Now what American mammal is marsupial?

*November 23, 2016*

**Science**

eg: http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html

*November 23, 2016*

**Science**

google kangaroo, marsupial :)

*November 23, 2016*

**help me plz**

I wish I knew what rt{t} meant but anyway we will need to do r of 9 and delta r for delta t at t = 9 r = t i + t^1.5 j + e^.25 t k dr/dt= i + 1.5 t^.5 j + .5 e^.25 t so dr (your delta r) = dt i + 1.5 t^.5 dt + .25 e^.25 t dt j Then r(9)= 9 i + 27 j+ 9.49 k dr = dt i + 4.5 dt j...

*November 23, 2016*

**calculus**

The DOMAIN is all real t HOWEVER the RANGE is only from -1 to +1 in i and -4 to + 4 in j and all real numbers in k

*November 23, 2016*

**History**

NO !!!!

*November 22, 2016*

**science**

Senpai - buying books instead of borrowing from the library uses up trees (as well as a lot of other stuff like fuel).

*November 22, 2016*

**science**

Which do you think Jaden? Think of the effect of each answer on trash heaps and energy supplies and forests.

*November 22, 2016*

**Science**

initial momentum = 1 kg * 7 m/s - 2 kg * 7/6 m/s = = 14/3 kg m/s final momentum is the same 14/3 = 1 * V1 + 2 * V2 so V1 = 14/3 - 2 V2 initial Ke = (1/2)(1)(49) + (1/2)(2)(49/36) final Ke = .75*initial Ke = (1/2)(1)V1^2 + (1/2)(2)V2^2

*November 22, 2016*

**PHYSICS PLEASE HELP ME**

force of gravity down slope = m g sin 30 = .5 m g force of friction up slope = FF use FF to get angular acceleration FF r = I alpha so alpha = FF r/I = FF r/(2/5 mr^2) alpha = 5FF/2mr FF = 2 m r alpha/5 a = r alpha so alpha = a/r and F = m a so m a = .5 m g - FF m a = .5 m g...

*November 22, 2016*

**math**

I do not know what your triangle looks like area outside triangle = circle area pi r^2 - triangle area

*November 22, 2016*

**maths**

volume of sphere = (4/3)pi r^3 pi R^2 h = (4/3) pi r^2 h = (4/3) r^2/R^2

*November 22, 2016*

**maths**

just like your other problem, your turn

*November 22, 2016*

**Physics- Equilibrium**

If I had to pick one it would be c. Constant velocity means no acceleration which means no net force.

*November 21, 2016*