Thursday

December 8, 2016
Total # Posts: 28,437

**maths**

http://www.gregthatcher.com/Mathematics/GaussJordan.aspx for the first one for example there are three rows and four columns 1 +1 +1 -3 1 -1 -2 13 1 +0 -4 25

*October 24, 2016*

**physics**

That is correct assuming that the ball is sliding, not rolling. If rolling there is a force back on the bottom of the ball to give it angular acceleration but I suspect you have not covered that. Let's just assume that is a net force of 3 N :) In other words the 3 N is the...

*October 24, 2016*

**Algebra**

150 miles /30 miles/gal = 5 gal

*October 24, 2016*

**I need help, I'm stuck...what is the correct answe**

There are 14 students 7 got less than 7.5 and 7 got more than 7.5 so 7.5 is median for mean 2(4)+2(5)+1(6)+2(7)+3(8)+4(10) =102 102/14 = 7.3

*October 24, 2016*

**American Government**

no taxes no army see: http://americanhistory.about.com/od/governmentandpolitics/f/articles_of_confederation_fails.htm

*October 24, 2016*

**maths**

divide 6 by 2 and square it, 9 x^2 - 6 x + 9 -9 (x-3)^2 - 3^2 3(x^2 + 20 x/3) (10/3)^2 = 100/9 3 [ x^2 + 20/3 x + (10/3)^2 - (10/3)^2 ] = 3 [ (x-10/3)^2 - (10/3)^2 ]

*October 24, 2016*

**physics**

gravity force down slope = m(acceleration down slope) m g sin 37.5 =(m v^2/r) cos 37.5 g tan 37.5 = v^2/r v^2 = r g tan 37.5 = 394*9.81 tan 37.5 v = 54.5 m/s

*October 23, 2016*

**advanced math**

16 + 169 = 185 = x^2 so x = square root of 185 = 185^0.5 = 13.6

*October 23, 2016*

**Math**

11/15 = .73 10/13 = .77 better

*October 23, 2016*

**Math**

legs = 4 p + 2 c = 52 p+c = 22 so p = 22-c 4(22-c) + 2 c = 52 88 - 2 c = 52 2 c = 36 c = 18 then p = 4

*October 23, 2016*

**Geometry**

tan 75 = 80/d d = 21.4 ft between buildings tan 62 = x/21.4 x = 40.3 = height abobe 80 so 120 ft

*October 23, 2016*

**Physics**

a = .09/480 = 9/48000 m/s^2 dv = a dt = (9/48,000) *7d/w*24h/d*3600s/h = 113 m/s we are assuming constant mass. Possibly fuel or even engine components were ejected. This is just the speed change due to the propulsion. Presumably there are also gravitational forces acting even...

*October 23, 2016*

**Physics**

energy stored in spring = (1/2) k x^2 = (1/2)(100)(.04) work done by friction = mu m g *d so 50*.04 = .2 * 1 *9.81* d solve for d

*October 23, 2016*

**math**

If they were 1 by 1 the diagonal would be 400 say n of them along each side diagonal is then n sqrt 2 =400 n = 400/sqrt 2 but n^2 is number of squares so answer = 400^2/2 =200*400 = 80,000 I suspect you mean the diagonal is 80 cm, not 800 by the way

*October 23, 2016*

**Math**

df = 4 dx so if you go from 3 to 2.9 that is dx = -.1 so df = -.4 and 5 - .4 = 4.6 sure enough

*October 23, 2016*

**EASY MATH FOR 4TH GRADE**

or 5 (3*1000 + 3*100 + 3*10 * 3*1) 15*1000 + 15*100 + 15 * 10 + 15*1 1*10,000+5*1000 + 1*1000+5*100 + 1*100+5*10 + 1*10 + 5 10,000 + 6,000 + 600 + 60 + 5 16,665 again I do not know how you are doing this in your class but suspect distributive property in some form.

*October 23, 2016*

**EASY MATH FOR 4TH GRADE**

5( 3000 + 300 + 30 + 3 ) 15,000 + 1,500 + 150 + 15 15,000 + 1,500 + 165 15,000 + 1,665 16,665

*October 23, 2016*

**Calculus**

x = 5 + 20 t y = -75 + 15 t z =distance =sqrt(25+5625) (I bet you meant 7.5 miles but oh well) dx/dt = 20 dy/dt = 15 at t = 0 x = 5 and y = -75 z^2 = x^2 + y^2 2 z dz = 2x dx + 2 y dy so dz = (x dx + y dy)/z and dz/dt = (x dx/dt + ydy/dt)/z = (5*20-75*15)/sqrt(25+56250

*October 23, 2016*

**Physics need R**

angular momentum of disk = (1/2) M R^2 omega final angular momentum of debris initial = m R^2 (v/R) = m v R so m v R = (1/2) M R^2 omega omega = 2 v (m/M) /R

*October 23, 2016*

**Chemistry (atoms)**

1 mole of water H2O has one mol of O so we have .0595 * 6.022*10^23 atoms

*October 23, 2016*

**MATH**

A = x y 50 x + 20 (2y) = 2000 or 5 x + 4 y = 200 5 x + 4 A/x = 200 5 x^2 - 200 x - 4A = 0 where is vertex of parabola? -b/2a = 200/10 =20 so x = 20 5(20) + 4 y = 200 4 y = 100 y = 25

*October 23, 2016*

**Physics**

s = speed 45.9 = u T where u = s cos 40 so T = 45.9 /(s cos 40) where T is time aloft rise time is half T or t = T/2 v = Vi - g t Vi = s sin 40 at top v = 0 s sin 40 = 9.81 t = 9.81[45.9/(2s cos 40] or 2 s^2 sin 40 cos 40 = 9.81*45.9 remember trig now

*October 22, 2016*

**physics**

m a = G m Mmoon /R^2 so 1.62 = G Mmoon/(1.738*10^6)^2

*October 22, 2016*

**Physics**

assume you mean cross product no what if they are perpendicular ?

*October 22, 2016*

**physics**

force = rate of change of momentum which is m a if the mass is constant 10 Newtons = change of momentum/0.10 second so change of momentum = 1 kg m/s by the way the change in speed would be 1/5 = .2 m/s

*October 22, 2016*

**questions all the same**

water density, rho, is about 1,000 kg/m^3 the mass of a column of water one square meter in cross section and h meters high is therefore: mass = rho * 1 * h = 1,000 h kilograms the weight of that mass is mg = 1,000 * 9.81 * h Newtons the pressure is that force over the one ...

*October 22, 2016*

**hold it**

Bob seems to be using vi both for vertical and horizontal speed I think in fact the original vertical speed is zero so h = Hi + 0 -4.9 t^2 1.8 = 21.9 - 4.9 t^2 t^2 = 4.1 t = 2.03 seconds to fall now the car has to go horizontal 58 meters in 2.03 seconds so I will call the ...

*October 21, 2016*

**solve what for t?**

Is it something like sin t = .5 or something?

*October 20, 2016*

**physics need asap help**

initial x momentum = m u initial y momentum = 2 m v final x momentum = 3 m (2) cos 37 final y momentum = 3 m (2) sin 37 so u = 6 cos 37 v = 3 sin 37

*October 20, 2016*

**physics need help**

integral of F(x) dx = a x^2/2 + b x^3/3 at 3 this is 9a/2 + 27b/3 at 1 it is a/2 + b/3 subtract 8a/2 - 26b/3 now put in a and b 40/2 + 52/3 etc

*October 20, 2016*

**history**

d is politically incorrect so you better pick c a is pretty funny as is b

*October 20, 2016*

**Algebra 2**

You can easily check this yourself. First 3 + 6 + 2 = 11 sure enough twice as many peanuts as almonds, yes total cost = 1.5*6 + 3*3 + 1.5*2 = 9 + 9 + 3 = 21 so yes, done

*October 20, 2016*

**Math**

takes time t for pump 1 the big one takes time 3 t for pump 2 so pump 1 does 1/t jobs/hr pump 2 does 1/3t jobs/hr (1/t + 1/3t) = 4/3t jobs/hr together (4/3t jobs/hr)9hr = 1 job 12 hours = t

*October 20, 2016*

**PHYSICS- PROJECTILE MOTION**

Your teacher is really trying to get to you with this separation of constant horizontal speed from increasing vertical speed. 89 * 3.10 centimeters if you really mean cm/s

*October 20, 2016*

**Pre algbra**

-20/30 - 9/30

*October 20, 2016*

**PHYSICS- PROJECTILE MOTION**

a) Trick question - it does not change. u = 1.90 b) v = -9.81 t so |v| = 9.81 (0.410) c) speed = sqrt (u^2+v^2) d) tan (angle down from horizontal) = |v|/u

*October 20, 2016*

**physics**

sqrt(9+4)

*October 19, 2016*

**Calculus**

line is y = -5 x + 3 so slope = -5 = slope of tangent f' = slope = 6 x - 7 where is that -5? 6 x - 7 = -5 6 x = 2 x = 1/3 so y = 3(1/9) -7(1/3) + 4

*October 19, 2016*

**History**

World War One?

*October 18, 2016*

**Physics**

Violet bends more than red the slower wavelength bends more so violet is slower

*October 18, 2016*

**nobody knows**

the other two sides must also have lengths.

*October 18, 2016*

**Physics**

f = sqrt (T/[m/L]) / 2L m = 8000 A L so 170 = sqrt (T/8000A)/4 680 = sqrt (T/8000A) also 1% = .01 = T/ (E A) so T/A = .01 E so 680 = sqrt (.01 E/8000) 462400 = .01 E/8000 E = 3.7 *10^11

*October 18, 2016*

**physics**

20 = (1/2)10 t^2 solve for t = 2 seconds d = 15 t =15*2 = 30 m

*October 18, 2016*

**physics**

The total momentum of the system can not change if there is no external force. Therefore 4

*October 18, 2016*

**Math Question**

parabola, not a line, because y is squared

*October 17, 2016*

**Math**

12 a + 8.5 s = 10,175 a+s = 950 so s = (950-a) 12 a + 8.5(950-a) = 10,175 12 a + 8075 - 8.5 a = 10,175 3.5 a = 2100 a = 600

*October 17, 2016*

**Math**

4x*1 = 4x

*October 17, 2016*

**math**

4x = 50 x = 12.5

*October 17, 2016*

**Algebra**

10x+4

*October 17, 2016*

**History**

How about basic language (Indo European) ?

*October 17, 2016*

**Engineering**

ABS density varies from 1.0 to 1.4 grams/cc you did not give any units except dollars .437 what? grams, pounds, kg , oz ?

*October 17, 2016*

**Nobody knows**

we do not know how much plastic each part takes

*October 17, 2016*

**Math**

21/4 + 41/16 is 84/16 + 41/16 your turn now

*October 17, 2016*

**math**

her speed = v current speed = 3 time up = 18/(v-3) time down = 18/(v+3) so 18[ 1/(v-3) + 1/(v+3) ] = 8 [ 1/(v-3) + 1/(v+3) ] = 4/9 [ v + 3 + v - 3 ] = (4/9)(v^2-9) 18 v = 4 v^2 - 36 2 v^2 - 9 v - 18 = 0 v = 6 for positive v root ----------------------------- check up speed = 3...

*October 17, 2016*

**Physics**

more like 12.7 did you take the square root? I think not :)

*October 17, 2016*

**Physics**

(1/2) v^2 = 9.81 (8.2) v^2 = 16.4*9.81

*October 17, 2016*

**math**

pi r^2 h = 25 so h = 25/(pi r^2) A = 2 pi r^2 + 2 pi r h but we know h(r) A = 2 pi r^2 + 2 pi r * 25/(pi r^2) A = 2 pi r^2 + 50/r r better be >0

*October 17, 2016*

**math**

he has made .4*20 = 8 of 20 he shoots total of 20 + x shots 8 + x = .5(20+x) 8 + x = 10 + .5 x .5 x = 2 x = 4 ==================== check he has now shot 24 and has made 8+4 = 12 sure enough 12/24 = .5

*October 17, 2016*

**math**

fewer dollars per oz or per pound is cheaper per pound of weight gained.

*October 17, 2016*

**Math**

1.5+1.2 = 2.7

*October 17, 2016*

**Maths**

How many do you think? Draw a picture.

*October 17, 2016*

**maths**

there are 2 pi radians in a circle C = 2 pi R so (2.5/2pi)(2 pi R) = 2.5 R = 2.5 * 8 = 20

*October 17, 2016*

**algrebra**

-6x = 2 x = -2/6 = -1/3

*October 17, 2016*

**Math**

1 1/2 = 3/2 (3/2)(42) = 3 (21) = 63

*October 17, 2016*

**I don't either**

I could say 7 + 31 + 6 = 44 low or 8 + 32 + 7 = 47 high but that would be kind of silly and I would be more likely to estimate using nearest whole numbers 8 + 31 + 7 = 46

*October 17, 2016*

**math**

L + w = 250 so L = 250-w L = 50 + w so 250 - w = 50 + w 2 w = 200 w = 100 L = 150

*October 17, 2016*

**Math**

LOL, ok dividing by 3 is the same as multiplying by 1/3 :)

*October 17, 2016*

**Math**

huh?

*October 17, 2016*

**Math**

(9/5)/3 = 3/5

*October 17, 2016*

**Math**

(-11/8)(14/5) = - (11/4)(7/5) = 77/20 = 3 17/20

*October 17, 2016*

**Math**

1.5 + 1.2

*October 17, 2016*

**8th pre algebra**

By the way that is algebra, not pre algebra :)

*October 17, 2016*

**8th pre algebra**

2(10) - 7 = ? sure enough 13 so you are right BUT actually you ADDED 7 to both sides

*October 17, 2016*

**Trig**

2sin 2Tcos2T/[1 + 2 cos^2 2T -1] = sin 2T cos 2T/ [cos 2T cos 2T] = sin 2T/cos 2T = tan 2T = 2 tan T/[1-tan^2T]

*October 17, 2016*

**math**

6.60/[12*710] or 9.18/[24*500] which is less dollars per mL ?

*October 17, 2016*

**Physics (Mechanics)**

m2 going up is + -m1 g + m2 g sin T= (m1+m2)a -2.5(9.8)+9.8m2 sin T=-(2.5+m2).108 -.8(9.8)+9.8m2sinT = (.8+m2)2.888 ---------------------------------- subtract to get rid of 9.8m2 sin T solve result for m2 go back and get m2 sinT and therefore sin T

*October 17, 2016*

**math (Help)**

if it has the square root of a variable in it (y^.5), it is not a straight line

*October 17, 2016*

**sure do need steve**

I can make no sense at all of your problem statement.

*October 17, 2016*

**Math Functions**

6000 + 1000 x

*October 17, 2016*

**Math Limits**

looks good to me

*October 17, 2016*

**Math**

It has y^2 in it. It is therefore a parabola, not a straight line e.

*October 17, 2016*

**physics**

v = Vi - 9.81 t at 1.7 s 19 = Vi - 9.81 (1.7) solve for Vi, launch speed at 5.4 s v = Vi - 9.81(5.4)

*October 17, 2016*

**algebra**

.55 V1 + .80 V2 = .6(50) and V1 + V2 = 50 so V2 = 50 - V1 .55 V1 + .8(50 -V1) = 30 etc

*October 17, 2016*

**History**

This is pretty important. What do you think?

*October 17, 2016*

**physics**

v = Vi - 9.81 t h = Hi + Vi t -4.9 t^2 ==================== 2.2 = 1.5 + 6.4 t - 4.9 t^2 solve quadratic for t then v = 6.4 - 9.81 t

*October 17, 2016*

**Physics**

72 km/hr = 72000/3600 = 20 m/s

*October 17, 2016*

**Math**

(6.4/2)100 = 320 %

*October 17, 2016*

**math**

you mean 2 - 3^2 ??? 2 - 9 = -7

*October 17, 2016*

**6th grade math**

another way to think about it: (3/4) pic / 1 sec = 6 pic/ x sec (3/4) x = 6 x = (4/3)6 x = 8 seconds

*October 17, 2016*

**6th grade math**

6 pictures[1 second/(3/4) picture] = 6 *4/3 = 8 seconds

*October 17, 2016*

**Geometry**

change in x = -15 change in y = -1 distance = sqrt(225+1) = sqrt(226)

*October 17, 2016*

**typo**

I mean .131/16 = .008 mols O

*October 17, 2016*

**Science (Chemistry) Ratio of mole**

If you had used mols O you would have had .13/.16 = .008 or two mols of O for every one of Mg so it would have been MgO2 anyway :)

*October 17, 2016*

**math**

L + w = 42 L + 3 = 4 w 42 - w + 3 = 4 w 5 w = 45 etc

*October 16, 2016*

**Physics**

normal force = m g cos 30 so friction force </= mu m g cos 30 can only say less than if object is not moving. component of weight down slope = m g sin 30 so if no other forces are acting m g sin 30 </= mu m g cos 30 or mu >/= tan 30

*October 16, 2016*

**Math**

maybe 1002001 ? That is a lot of km 2000 km / (35 + 48 + 45.5) = 15.56 km/L = 6.43 L/100 km

*October 16, 2016*

**physics**

http://www.physicsclassroom.com/class/sound/Lesson-5/Closed-End-Air-Columns

*October 16, 2016*

**Physics Force and Friction question**

max static friction force = .4*981 which is more than 350 so It stays in place. 350 N might be enough to keep it moving, but is not enough to start it.

*October 16, 2016*

**need more info**

Is it barely not moving, is it moving at constant velocity, is it accelerating?

*October 16, 2016*

**Math( 7th grade advanced math so 8th grade math)**

A = 3 x + 59 + 2*35 = 3x + 129

*October 16, 2016*