Saturday

August 23, 2014

August 23, 2014

Total # Posts: 17,991

**Physics**

When a wave travels from fast to slow medium: Reflected wave is inverted. (crest -reflected as trough is 180 deg phase shift)
*July 26, 2014*

**Algebra**

Sketch those lines slopes of +/- 1 center axis halfway between 1 and 5 so at y = 3 the lines cross at (2,3), so that is center of hyperbola so (x-2)^2/a^2 - (y-3)^2/b^2 = 1 slopes of asymptotes = +/- b/a so b = a (x-2)^2/a^2 - (y-3)^2/a^2 = 1 put that point in now (4-2)^2/a^2...
*July 26, 2014*

**Physics -- check answers please**

1. ok 2. We used to use a "diffraction grating" in the spectroscopy lab to get the clearest pattern.
*July 26, 2014*

**Calc**

Oh, sorry, I thought you meant just the length of that splitting fence.
*July 25, 2014*

**Calc**

.000000000000001 feet or perhaps the length of the width of a cow. :) The problem does not make much sense as stated. You could make the field extremely longs and not at all wide and divide it with a little fence in the middle the length of your very short ends.
*July 25, 2014*

**algebra 1**

well, do part B and you will have the answer to part A 100 - 1.9 = 98.1 percent so every time we go a meter, we multiply by .981 after x meters f(x) = 1700 * .981^x (Part B answer) which is exponential, not linear. (part A answer) It does not lose a constant "amount"...
*July 25, 2014*

**Calculus: Determine the constants from function**

dh/dx = 0 at critical points dh/dx = 3 x^2 + 2 b x = 0 x (3x+2b) = 0 so at (2,4), 3x+2b = 0 = 6 + 2b so b = -3 so h = x^3 -3 x^2 + d at x = 2, h = -4 -4 = 8 - 12 + d d = 0 so h = x^3 -3 x^2
*July 25, 2014*

**College Algebra**

^4t not to the t/4 1.01875^4t = 7200 4 t = log 7200/log 1.01875 t = 120 years
*July 25, 2014*

**Math 221**

That is: https://www.khanacademy.org/math/linear-algebra/vectors_and_spaces/vectors/v/linear-algebra--parametric-representations-of-lines
*July 25, 2014*

**Math 221**

Your talk of origins does not make a lot of sense to me since the origin is at (0,0) for all your problems. However perhaps your class is trying to work toward a vector version of this material where you specify a point and move out from there at a certain slope. In that case ...
*July 25, 2014*

**Math 221**

If y = x + 8 the x axis intercept for that is when y = 0 0 = x + 8 x = -8 so (-8,0) the y axis intercept for that is when x = 0 which is b in y = m x + b so 8 so at (0, 8) --------------------------------------- I thought I did that other one too. This time you did the problem...
*July 25, 2014*

**Math 221**

Go back, I just saw this below and replied. http://www.jiskha.com/display.cgi?id=1406309814
*July 25, 2014*

**MAth**

10 y^2 - 15 y + 2 y - 3 or 10 y^2 - 13 y - 3
*July 25, 2014*

**Physics**

I do not have your figure. HOWEVER (Note - I do not care what mass it is, call it m not 200 until part c) initial kinetic energy = (1/2)m(100) = 50 m Ke at any height h = 50 m + m g (100-h) so at any height h (Points A B and C) (1/2) m v^2 = 50 m + m g (100-h) note m cancels) ...
*July 25, 2014*

**math**

You are welcome.
*July 25, 2014*

**math**

n on shelf .5 n are #1 .25 * .5 n = .125 n are #3 .5 n + .125 n = .625 n are either #1 or #3 so 1 n-.625 n = .375 n = 5 n = 5/.375 = 13 1/3 hmmmm, I hope we have a fractional bookcase
*July 25, 2014*

**math**

so, like maybe they were 270 miles apart and collided at x pm :) they approach each other at 45 miles/hr 270 miles/45 miles/hr = 6 hours 6+5 = 11 pm
*July 25, 2014*

**science**

No, but note that they grow back after a few weeks ! http://birds.about.com/od/grooming/a/How-To-Clip-Your-Birds-Wings.htm
*July 25, 2014*

**Math 221**

typo yp should be y1
*July 25, 2014*

**Math 221**

Oh, I see what you are doing. given y = x + 4 we want parallel and through (-7,1) since y = 1 x + 4 has slope = m = 1 ANY parallel line ALSO has slope = 1 slope = 1 = (y-yp)/(x - x1) or 1 = ( y - 1 ) / (x - -7) 1 = (y-1) / (x+7) y-1 = x + 7 y = x + 8 I like my way better, but ...
*July 25, 2014*

**Math 221**

The origin is always at (0,0) However none of your lines go through the origin.
*July 25, 2014*

**Math 221**

yes I did not entirely follow all your steps though. The way I do it y = 1 x + 4 m = 1, so my new m must be 1 also if parallel ( I did not follow you here) point is (-7, 1) 1 = 1(-7) + b yes b = 8 y = x + 8
*July 25, 2014*

**do not understand**

I can not fathom your notation.
*July 25, 2014*

**Math 221**

assume you mean y = (-1/2) x + 1 slope m = -1/2 so slope of perpendicular = -1/m = 2 y = 2 x + b put in point 2 = 2(4) + b b = -6 so I agree y = 2 x - 6 You are getting these right but not the way I do them and I have not figured out what you are doing yet.
*July 25, 2014*

**Math 221**

I think I just did these above.
*July 25, 2014*

**math**

how many combinations of three from 5 n!/[ r!(n-r)! ] 5!/[2!(3!)] = 10 or do one by 1 the hard way A B - C, D, E --> 3 A C - D, E -->2 A D - E -->1 B C - D, E -->2 B D - E -->1 C D - A -->1 3+2+1+2+1+1 = 10
*July 25, 2014*

**Math**

I got 120
*July 24, 2014*

**Math**

Adults = .6 * 840 = 504 children = .4 * 840 = 336 504 = .7 (840 - boys)
*July 24, 2014*

**MATH**

profit = .2 S cost = 72 72 + .2 s = s 72 = .8 s s = 90 =============================== Javier had J = 28 28 + (4/5) D = 64 (4/5) D = 36 D = 45
*July 24, 2014*

**Math**

perimeter = 4 x so x = 15 area = 225 -------------------- A does task/r per day B does task/s per day [ 1/r + 1/s ] task/day together so 1/ [ 1/r + 1/s ] = r s / (r+s) or r s ------- r + s which is probably d) but you left the parentheses out
*July 24, 2014*

**statistic**

I can not see your problems. Copy and paste does not work here. However I am sure this link will do the trick anyway: http://davidmlane.com/hyperstat/z_table.html
*July 24, 2014*

**Math: Zeroes**

Oh, 50 factorial 50 * 49 * 48 ..... 1 3.0414093e+64 so 64 Just GOOGLE 50 factorial
*July 24, 2014*

**Math: Zeroes**

I would just write the list out if I could not guess :) You could shorten the task as so: 1 ----- 10 11 -----20 21 -----30 31 .....40 41 .....50 :-)> . .
*July 24, 2014*

**Chemistry**

you have two Mg for every one O2 so mols Mg/mols O2 = 2/1 3 mols Mg ( 1 mol O2 / 2 mols Mg) = 3/2 = 1.5 mols O2 ----- Yes 1 O2/2 MgO 3 O2 ( 2 MgO/1 O2 ) = 6 MgO
*July 24, 2014*

**typo**

By the way, if you happen to know Physics: v = Vi - 32 t at top v = 0 0 = 56 - 32 t t = 1.75 seconds 32 ft/sec^2 = acceleration of gravity in these obsolete units
*July 24, 2014*

**Math**

By the way, if you happen to know Physics: v = Vi - 32 t at top t = 0 0 = 56 - 32 t t = 1.75 seconds
*July 24, 2014*

**Math**

feet units drive me crazy but all right. 16 t^2 - 56 t - 1 = -h 16 t^2 - 56 t = - h + 1 t^2 - 3.5 t = - h/16 + 1/16 t^2 - 3.5 t + (3.5/2)^2 = -h/16 + 1/16 + 12.25/4 (t - 3.5/2)^2 = ...... vertex (top) when t = 3.5/2 = 1.75 seconds if they ask how high, keep going with ...
*July 24, 2014*

**Math**

2 x - 2 = x^2 - x - 6 x^2 - 3 x - 4 = 0 (x-4)(x+1) = 0 x = 4 or x = -1 y = 6 or y = -4 so (4,6) and (-1,-4)
*July 24, 2014*

**calculus**

well first of all it asked for the intercepts where does the first one hit the x axis? x (x^2 -6 x+ 9) = 0 x (x-3)(x-3) = 0 so x axis intercepts at x = 0 and x = 3 (twice which means that is a grazing or min or max of g Where does the first one hit the g axis? when x = 0, y = ...
*July 24, 2014*

**PhysicsI**

thickness = .005 meter Q =0.84 * Area * (delta T) /thickness = 0.84 * 1 * 15 /.005 Joules/second which is Watts by the way
*July 24, 2014*

**statistics**

http://davidmlane.com/hyperstat/z_table.html
*July 24, 2014*

**Geography**

A "dormant" volcano is one that has not erupted for a while and is not expected to do so in the near future. It is not "extinct" though and will probably erupt sometime in the future. See: https://www.google.com/search?q=dormant+volcano+definition&ie=utf-8&...
*July 24, 2014*

**Homework dumping**

There has been no sign of any effort by the student to do these problems.
*July 23, 2014*

**calculating statistical data**

Where is your attempt to solve these problems?
*July 23, 2014*

**Physics**

k Q1 Q2 / d^2 d2 = .5 d1 so d2^2 = .25 d1^2 1/.25 = 4 times like charges repel and for heavens sake READ THE BOOK !!!!
*July 23, 2014*

**I have no idea.**

Need volume of tank and volume of a carton
*July 23, 2014*

**science**

It is NOT MOVING (This is a trick question) total energy = (1/2) k x^2 = (1/2)(15.6)(.04)
*July 23, 2014*

**Maths.literacy**

Oh, I see, you asked question above assuming I had seen this one. volume of tank = pi r^2 L = pi (2.25)(3) meters cubed 1 kiloliter = 1 meter cubed However I do NOT know the volume of a carton of milk (perhaps one liter? Perhaps half a liter?)
*July 23, 2014*

**Physics**

L = I omega I = m r^2 = 90 * 40^2 omega = v/r = 5 /40 so L = 90 * 40^2 * 5 /40 = 90 * 200 = 18000
*July 23, 2014*

**mathematics**

first one fills 1 truck /12 min second fills 1 truck/6 min so together they fill (1/12 + 2/12) trucks per min which is 1/4 of a truck per minute or four minutes per truck. Get it?
*July 23, 2014*

**math**

bought x gallons dining room = (x/3) gallons kitchen = 1.5 gallons living rm = 3 gallons leftover = 1.5 gallons so (x/3) + 6 = x 6 = 2 x/3 x = 9 gallons
*July 23, 2014*

**something wrong here I think**

You have over defined this problem. Once you say 23.5 meters in 5 seconds you have set the horizontal speed u = 23.5/5 Now if you set the angle at 35 then u = initial speed * cos 35 so solve for the initial speed However now we have a dilemna. Vi = initial speed up = initial ...
*July 23, 2014*

**algebra**

Hey, I did one, your turn :)
*July 22, 2014*

**math**

3^5 + ***** 3^4 (bx) + ****** 3^3 (bx)^2 + ........ now get binomial coefficients for fifth power from Pascal's triangle or formula 1 5 10 10 5 1 so 3^5 + 5*3^4 b x + 10 * 3^3 b^2 x^2 243 + 405 b x + 270 b^2 x^2 ......
*July 22, 2014*

**calculus**

Nor do I
*July 22, 2014*

**calculus typo**

y = x^(2/3) at x = 1 which is b y = 1^(2/3) = 1 at x = 0 which is a y = 0^0 = 0 y(1) - y(0) = 1 - 0 = 1 b - a = 1 - 0 = 1 so 1/1 = 1 so according to the mean value theorem somewhere between x = 0 and x = 1 the derivative = 1 dy/dx = (2/3) x^-1/3 = (2/3)/x^(1/3) when is that ...
*July 22, 2014*

**calculus**

y = x^(2/3) at x = 1 which is b y = 1^(2/3) = 1 at x = 0 which is a y = 1^0 = 1 y(1) - y(0) = 1 - 0 = 1 b - a = 1 - 0 = 1 so 1/1 = 1 so according to the mean value theorem somewhere between x = 0 and x = 1 the derivative = 1 dy/dx = (2/3) x^-1/3 = (2/3)/x^(1/3) when is that ...
*July 22, 2014*

**Calculus**

y = 2 (x+5)^3 + 7 to make this really easy you can say z = x+5 then dz/dx = 1 y = 2 z^3 + 7 dy/dz = 6 z^2 d^2y/dz^2 = 12 z so dy/dx = dy/dz * dz/dx = 6(x^2+10x+25) when is that zero ? (x+5)(x+5) = 0 x = -5 twice what is d/dx (dy/dx)? 6 ( 2 x + 10) when x = -5 2(-5)+10 = 0 so ...
*July 22, 2014*

**physics typo**

physics - Damon, Tuesday, July 22, 2014 at 4:37am Newton #1 - If there is no NET force, momentum is constant. Here speed is steady (I assume in a straight course) and mass is constant so net force is zero. Newton #3 - Action is equal and opposite to reaction. So Propulsion ...
*July 22, 2014*

**physics**

Newton #1 - If there is no NET force, momentum is constant. Here speed is steady (I assume in a straight course) and mass is constant so net force is zero. Newton #2 - Action is equal and opposite to reaction. So Propulsion force forward must be equal and opposite to ...
*July 22, 2014*

**Math 221*revised***

You can enter that as 5' 2" in the web site I gave you: http://www.mayoclinic.org/bmi-calculator/itt-20084938
*July 22, 2014*

**Math 221**

http://www.mayoclinic.org/bmi-calculator/itt-20084938 You need male or female and birth date.
*July 21, 2014*

**Physics**

vertical problem first h = Hi + Vi t - 4.9 t^2 0 = 80 + 300 (sin 30) t - 4.9 t^2 solve quadratic for t. Use positive t, the other root was on the way up underground. then Horizontal problem at constant u = 300 cos 30 d = u * t
*July 21, 2014*

**Physics**

What might happen if you increased the volume?
*July 20, 2014*

**Physics**

http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Gas%20laws/text/Adiabatic_change_equation/index.html Note example problem with adiabatic expansion to twice volume.
*July 20, 2014*

**physics**

horizontal pull = 20 cos 60 = 10 N vertical pull up = 20 sin 60 = 17.3 N normal force = m g - 17.3 friction force = .4 (9.81 m - 17.3) = 3.92 m - 6.92 so 3.92 m - 6.92 = 10
*July 20, 2014*

**math**

Carrie = 1 case / 5 hours = .2 case/hr James = 1 case/3 hours = .333 case/hr together they do .533 case/hr so .2 * 1 hr + .533 * x hr = 1 case .533 x = .8 x = 1.5 hours more
*July 17, 2014*

**physics**

It is a loop of wire operating in a changing magnetic field, changing because sometimes the B flux is through the plane of the coil and sometimes it is parallel to the plane of the coil and no B goes through the coil. B = 1.8 Tesla B through coil = 1.8 sin 2 pi f t f = 60 so 2...
*July 17, 2014*

**Calc**

You are welcome.
*July 17, 2014*

**Calc**

You forgot dx :) Now I just did one of these a couple of questions down. This time use rectangles with the left hand height. Evaluate left hand heights of function at 12 13 14 15 spacing is one so multiply each left hand height by 1 and add
*July 17, 2014*

**Science**

ni sin i = nr sin r 1 sin 50 = nr sin 40 nr = sin 50 / sin 40
*July 17, 2014*

**Calc**

I assume you mean v(t) = t^2 + 2 I am not going to do the four trapezoids for you but I will do the integral so you know if you have done the area right. s(t) = (1/3) t^3 + 2 t + c when t = 0, let s = 0 so let c = 0 (we could chose any old starting s and resulting constant c ...
*July 17, 2014*

**Math**

I bet "original" is "wholesale" :) multiply original by 1.20 then by 0.75 1.2*3/4 = .9 so 145 * .9 = $130.50
*July 17, 2014*

**Calc**

Oh and by the way when x = 0 we have 0/1
*July 17, 2014*

**Calc**

df/dx = - x e^-x + e^-x = 0 for max or min within interval BUT you did not say the interval in general e^-x = x e^x 1 = x is one place where the slope is zero is the second derivative + or - ? d^2f/dx^2 = -x(-e^-x) -e^-x - e^-x = xe^-x -2 e^-x) = (1/e^x)(x-2) when x = 1 = (1/e...
*July 17, 2014*

**science**

force * time = change of momentum a) force = 49 * (6-0) / 3 = 98 N b) force acts on the average over one hundred meters c) work = force * distance = 98 * 100 = 9800 Joules interesting, lets see how much kinetic energy we have (1/2) m v^2 = .5 * 49 * 36 = 882 Joules s we are ...
*July 17, 2014*

**Math**

always multiply by one (top equal to bottom) so the units come out with the unwanted ones canceling 23 cm * (1 meter / 100 cm) note cm cancels top and bottom, left with meters besides we all know 23 cm = 0.23 meters :) b) NO !! 1000 mm / one meter = one 5 m * (1000 mm / 1 m...
*July 17, 2014*

**physics**

I bet they both hit the ground at the same time, whenever that is.
*July 17, 2014*

**where asre the = signs?Math**

I do not understand this.
*July 16, 2014*

**Alegbra**

subtract negative 40 from positive 119 or simply add 119 and 40 +119 - (-40) simplified = 119 + 40 = 159
*July 16, 2014*

**science**

Open the box and take the hard drive, or simply take the computer.
*July 16, 2014*

**American literature**

"...... community.(256)..... " What is your reference number 256 ?
*July 16, 2014*

**calculus**

Profit = Revenue - Cost P = -q^3 + 60 q^2 +(-1200+551)q - 760 dp/dq = -3 q^2 +120q - 649 zero for max or min q^2 - 40 q + 216.333... = 0 q = [ 40 +/-sqrt (1600-865)]/2 q = [40+/-27.1)/2 q = 34 or 6.5 to find out if max or min, take next derivative d^2p/dq^2 = -6q +120 at q = ...
*July 16, 2014*

**physics 2**

I do not understand. Mass of object increases above rest mass as speed of light is approached. .08 times original mass????
*July 16, 2014*

**physics**

energy to water per second = 1.86*10^8 Joules Kg water per second heated = m 1.86*10^8 = 4184 * m * 2
*July 16, 2014*

**US Government**

The answer is in the link Ms. Sue gave you.
*July 15, 2014*

**Alegbra**

It is very difficult to fit a line to one point.
*July 15, 2014*

**Alegbra**

both sides are 0 at (6,-8) then y goes down 5 times as fast as x goes up check: from that point go right 1 and down 5 (7, -13) is that on the line? -13 + 8 = ???? -5 (7-6) -5 = -5(1) sure enough
*July 15, 2014*

**Alegbra**

y = m x + b 7 = 0 + b b = 7 so y = -6 x + 7 where does that hit x axis ? 0 = -6 x + 7 x = 7/6 so (7/6 , 0) draw line through (7/6 , 0) and (0 , 7)
*July 15, 2014*

**Geometry**

2 pi r = 2 pi (2x) = 4 pi x
*July 15, 2014*

**Physics mit 2.01x**

No (former MIT professor), I do not do MITx problems in Course 8 or Course 2. You are on your own. The 8.01x crowd swamped this board the last time around.
*July 15, 2014*

**science**

pi r^2 h pi 1*1*12 = 12 pi cm^3 or cc = 37.7 cubic centimeters
*July 15, 2014*

**physics**

a) Huh? at x = 0 and t = 0 , y = 0 so the phase constant is 0 b) at x = .0229 m and t = .197 .745(.0229) - 42.9(.197) = -8.434 radians = -482 degrees which is -360 - 123 degrees
*July 15, 2014*

**physics**

well, first do the vertical problem, the ball how long does it take to fall 20 m? 20 = (1/2) (10) t^2 t^2 = 4 t = 2 seconds so it will take to seconds to fall. By symmetry it will also take 2 seconds to rise and hit the plane how fast is it going when it hits the ground? u = a...
*July 15, 2014*

**physics**

by the way part B is also the average speed times the time x = 5.25 * 5.2
*July 15, 2014*

**physics**

a = change in velocity / change in time = ( 0 - 10.5) / 5.2 m/s^2 x = (1/2) a t^2 = (1/2) * a from above * (5.2) * (5.2)
*July 15, 2014*

**SCI 207**

I suppose those are the people with expensive houses on the shore. However what is meant by "worst impacts"? If it means losing the most money it may be correct. However wealthy people probably can survive the loss of shore side property without ending up homeless. ...
*July 15, 2014*

**physics**

To go from km/h to m/s divide by 3.6 which is 1000 m/km / 3600 s/min a = change in velocity/time (note it is negative) F = m a By the way, this ignores wave resistance which would be a major part of the retarding force.
*July 15, 2014*

**chemistry**

P1 V1 = P2 V2 so V2 = P1 V1/P2 I am assuming that these are total pressures and no "gage" pressures. If they are gage pressures add 1 atm to both P1 and P2
*July 15, 2014*

**physics**

well, I guess it is ok to use g = 9.81 m/s^2 but we will have to check later if the thing is a significant fraction of an earth radius high. (1/2) m v^2 = m g h v^2 = 2 g h h = v^2/19.6 = 49*10^4 / 19.6 = 25,000 meters that is a small fraction of earth radius so constant g ...
*July 13, 2014*

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