# Posts by Damon

Total # Posts: 29,627

**physic**

up for time t then down for time t (parabola) u = 100 cos 45 forever Vi = 100 sin 45 at start v = Vi - g t at top v = 0 so at top t = Vi/g = 100 sin 45 / 9.81 in the air for time = 2 t so range = 2 t u = 2 t (100 cos 45)

*January 14, 2017*

**Calc**

f = ln g df/dx = df/dg * dg/dx we were given dg/dx what is df/dg ? df/dg = d ln g / dg = 1/g so df/dx = (1/g)tan 2/(1+x^2) I think you mean = (1/5)tan 2/2 = (1/4) tan one radian or 180/pi deg = (1/5)(1.055741 ) = .31148 so agree

*January 14, 2017*

**physics**

do horizontal and vertical separately I assume j is up v = 13 - 9.81 t y = 0 + 13 t -4.9 t^2 If y is negative, it dug a hole :) and x = 12 t so d = 12 t i + (13t-4.9t^2) j

*January 13, 2017*

**math**

we have 9 * 300 = 2700 bee months of honey we now have 450 bees 2700 bee months / 450 bees = 6 months

*January 13, 2017*

**physics**

The trick here is guessing the drag coefficient of the raindrop shape. See: http://home2.fvcc.edu/~dhicketh/DiffEqns/Spring11projects/Ben_Lynch_Gavin_Lommatsch/DiffEqProject/DiffEqProjectGavinBen.pdf It is a function of Reynolds number even if the shape is spherical. However ...

*January 13, 2017*

**mathematics**

original, then difference, then difference of difference 2 ...... 3 5 ........... 2 .......5 10 .......... 2 .......7 17 ...........2 .......9 26 constant difference of differences is parabola well, y = x^2 + 1 works an = n^2+1

*January 13, 2017*

**What?**

Check for typos please. If you mean merged, same total volume, then with the same height, the base areas add up to the original. pi R^2 = pi r1^2 + pi r2^2 R2 = sqrt( r1^2 + r2^2)

*January 13, 2017*

**maths**

of course the area of ABC = (1/2)(3*4) = 6 :) also (1/2)(AD)(5) = 6 AD = 12/5 = 2.4 cm

*January 13, 2017*

**The cay is the book**

C is the only choice that indicates determination.

*January 13, 2017*

**Physics**

how long does it take to get from 100 to 30? v = vi + a t 30 = 100 - 4 t 4 t = 70 t = 17.5 s how far did we go? average speed = 130/2 = 65 65*17.5 = 1137.5 ft how far did the freight go? 30 * 17.5 = 525 525 + 600 = 1125 ft CRASH for part b x1 = 100 t - 2 t^2 x2 = 600 + 30 t ...

*January 13, 2017*

**math**

No, slant height is hypotenuse of triangle where altitude is one leg and half the base is the other.

*January 12, 2017*

**Computing**

n = 1 10 output = n*n print output n = n+1 if n = 6 quit otherwise go back up to 10

*January 12, 2017*

**maths**

3.14159.... is between 3 and 4

*January 12, 2017*

**physics**

I guess he is JUST prevented from slipping normal force = m g cos 43 force down slope = m g sin 43 so m g sin 43 = 520

*January 11, 2017*

**physics**

The same. If there is no acceleration there is no change in force (ignoring friction).

*January 11, 2017*

**Direction?**

Forces are vectors. If they are equal in magnitude but opposite in direction, they add to zero. If both in the same direction, then twice. If in between, then in between.

*January 11, 2017*

**physics**

Find the resultant of the two perpendicular forces |F| = sqrt (76.5^2+46.3^2) tan A = 76.5/46.3 where A is angle north of west our force is equal and opposite same |F| same angle but south of east

*January 11, 2017*

**math**

c = 3(c+3) -3(c-3) c = 3 c + 9 - 3 c + 9 c = 18

*January 10, 2017*

**pure physics**

Weight of water displaced = .25-.20 = .05 N which is the force up on the stone from the water.

*January 10, 2017*

**error**

2 a - 62 = 12 2 a = 74 !!!!! a = 37 b = 25 same answer anyway

*January 9, 2017*

**Algebra**

a+b = 62 so b = (62-a) a - b = 12 a -(62-a) = 12 2 a - 62 = 12 2 a = 50 a = 25 b = 62-25 = 37

*January 9, 2017*

**Math**

24/2.5 = 9.6 so 9 strips with a little left over but not really because some is lost in the kerf (the width of the blade)

*January 9, 2017*

**Math, Physics**

F = m g g = gsurface * Rearth^2/R^2 = 9.81 * Rearth^2/(Rearth+401500)^2

*January 9, 2017*

**Math**

A = x*y 32 = x+2y x = 32-2y A = (32-2y)y = 32y-2y^2 or y^2-16y = -A/2 you did not say if you are in algebra or calculus so I will do it the algebra way by completing the square y^2 -16y + (16/2)^2 = -A/2 + 64 (y-8)^2 = -(1/2)(A-128) y = 8 x = 16 and the area is 128 ft^2

*January 9, 2017*

**please show your attempts**

We are teachers. We do not do tessts for people.

*January 9, 2017*

**physics**

+250 :) weight = m g = 55*9.8 = 539 Newtons That is the normal force on the floor Max friction = .56*539 = 302 N

*January 8, 2017*

**physics**

weight = w = m g normal force = m g cos theta ratio = cos theta so cos 17 and cos 30

*January 8, 2017*

**calculus**

Oh, intercepts y = x^3-6x^2 0 = x^2 (x-6) bounced off x axis at x = 0 crossed x axis at x = 6

*January 8, 2017*

**calculus**

slope = 3 x^2 -12 x =3 x (x-4) second derivative (curvature) = 6 x - 12 so the slope is 0 at x = 0 and at x = 4 at x = 0 is that a min or a max or in inflection point? second derivative = -12 That is a maximum, starts down from there at x = 4 is that a min or a max or an ...

*January 8, 2017*

**Chemistry**

CuCO3 = 64+12+48 g/mol = 124 g 31/124 = .25 mol CO2 = 12+32 = 44 g/mol so 11 g for .25 mol for CuO, subtract:) 31-11 = 20 grams check: CuO = 64+16 = 80 g/mol .25*80 = 20 grams sure enough

*January 8, 2017*

**calculus**

two negative numbers can not add to +1

*January 8, 2017*

**calculus**

b.f(x)=x^3=x-4 Typo, makes no sense c. f(2)=8 f(-1)=-1 so 9/3 average slope =3 f' =3x^2 3 x^2 =3 x= sqrt(1) which is 1 !!!! but also -1 d f(4) = 2 f(0) = 0 so slope = 2/4 = 1/2 f' = (1/2)x^-1/2 = 1/2 x = 1 again

*January 8, 2017*

**Math**

a + b + c = 975 a - x = 12 b - x = 345 c - x = 126 --------------add a+b+c -3 x = 483 so 975 - 3 x = 483 3 x = 492 x = 164

*January 8, 2017*

**physics**

mapple Vapple +mweath*0 = (mapple+mearth) V V = Vapple (mapple)/(mapple+mearth) so yes mapple/(mapple+mearth) is not very big it might be kind of hard to measure :)

*January 8, 2017*

**physics**

The earth moves under your feet (but just a little).

*January 8, 2017*

**Math**

L(1-cosT) = 1/3 foot sin T = 4 feet/L so L sin T =4 1-cosT = 1/3L L sinT = 4 cosT = (3L-1)/3L so cos^2T = (9L^2 -6L+1)/9L^2 so 1-cos^2T = (6L-1)/9L^2 which is sin^2 T but sin^2T =16/L^2 so 16/L^2 = (6L-1)/9L^2 144 = 6L-1 6L = 145 L = 24.2 feet check my arithmetic!

*January 8, 2017*

**calculus**

dV = surface area * dr so dr/dt = dV/dt/(4 pi r^2) dr/dt = 2 /(4 pi *64)

*January 8, 2017*

**math**

well, you just said math, not calculus, which is why I completed the square to find the vertex of the parabola in the other problem. 3 4 5 triangle x = 4 y = 3 hypotenuse = 5 dy/dt = -2 ============================= x^2 + y^2 = 25 2 x dx/dt + 2 y dy/dt = 0 dx/dy = -(y/x)dy/dt...

*January 8, 2017*

**math**

r = x (1000-2x) r = 1000 x -2 x^2 2 x^2 -1000 x = -r x^2 - 500 x = -(1/2)r x^2 -500 x + 250^2 = -(1/2)r + 250^2 (x-250)^2 = -(1/2)(r-2(250)^2 ) x = 250 r = 2*250^2 = 125,000

*January 8, 2017*

**Algebra**

[ (x/3) -5 ] 7 = 28 (x/3) -5 = 4 x/3 = 9 x = 27

*January 8, 2017*

**calculus**

check end points f(-2) = -2+8 = 6 f(2) = 2-8 = -6 now find where derivative is zero f' = 1 -3x^2 = 0 when x = 1/sqrt3 or x = -1/sqrt3 if x = 1/sqrt 3 f = 1/sqrt3 -1/3sqrt3 =(2/3sqrt3) if x = -1/sqrt3 f = -1/sqrt3 +1/3sqrt 3 = -(2/3sqrt3) so the max and min are at the end ...

*January 8, 2017*

**calculus**

Well, try one of them. function is continuous and differentiable from 1 to 3 (note not at zero) f(3) = 3-1/3 = 8/3 f(1) = 0 [f(3)-f(1)]/(3-1) = 4/3 so where is the derivative 4/3? f'(x) = 1 + 1/x^2 where does 1+1/x^2 = 4/3 ? 1/x^2 = 1/3 x = sqrt 3 yes, that is between x = ...

*January 8, 2017*

**Physics**

pm=1.6gcm^-3 nonsense V = 40 cm^3 so mass = 20 + 40 * density of Hg which is not 1.6 g/cm^3

*January 8, 2017*

**Math**

original = p cents / pizza 10 p = total cost 9(p+60) = same total cost so 10 p = 9(p+60) p =540 cents = 5.40 per pizza so $54

*January 7, 2017*

**math**

n = original 1.2 n = before 300 .2 * 1.2 n = 300 so 1.2 n = 1500 n = 1250 books originally ===================== check ===================== 1.2 * 1250 = 1500 +300 = 1800 1.2*1.2*1250 = 1800 sure enough

*January 7, 2017*

**Algebra 1**

x = [2p+/-sqrt(4p^2+32p^2) ]2 = [2 p + sqrt(36 p^2) ]/2 = [2 p + 6 p ]/2 = 4 p

*January 7, 2017*

**Math**

(43/2)(3/4)= 129/8 left after tacos (2/3)(129/8) used for burgers times 4 for number of 1/4 lb burgers 4(2/3)(129/8) = 129/3 = 43 burgers

*January 7, 2017*

**another subtraction error**

360 - 12 = 348 348 = 23 t -23t/2 696 = 23 t t = 30.3 a = 23/30.3 = .759 m/s^2

*January 7, 2017*

**Physics**

freight train goes 6 t our train goes 6t+360 Vi = 29 Vf = 6 a assumed negative v = Vi - a t 6 = 29 - a t a t = 23 d = 6t+360 = 29t-(1/2)a t^2 360 = 23 t -(1/2)(23 t) 720 = 23 t t = 31.3 seconds to crash a = .74 whoops, forgot the .4 seconds to react we go 14.5 m he goes 2.4 m ...

*January 7, 2017*

**Algebra 1**

You are welcome.

*January 7, 2017*

**Algebra 1**

n + n+1 + n+2 + n+3 + n+4 = 5 n + 10 so (5n+10)/5 = 13 5n+10 = 65 5 n = 55 n = 11 so 11 , 12, 13 , 14, 15 old sum was 65 new sum is 53 difference is 12 so 12

*January 7, 2017*

**Physics**

Not really. I bet you have heard the word "Impulse" that is force * time which is change of momentum F = m a = m dv/dt so F dt = m dv = "impulse" but m dv is change in m v and m v is "momentum therefore F * time = change in momentum = impulse

*January 7, 2017*

**Physics**

change in momentum = force * time force up = 800 -55(9.81) = 260 N net up force so momentum = m Vi = 260*.25 = 65 so Vi = 65/55 = 1.18 m/s up (1/2)mVi^2 = m g h h = Vi^2/[2(9.81)] = .071 meters = 7.1 cm

*January 7, 2017*

**algebra**

x^2 - 3 x = 4 x^2 -3 x +(3/2)^2 = 4 + 9/4 (x-1.5)^2 = (1/4)(16 + 9) (x-1.5)^2 = (1/4)(25) = 25/4 x-3/2 = +/- 5/2 x = 3/2 +/- 5/2 x = 4 or x = -1

*January 7, 2017*

**Algebra 2**

You are welcome.

*January 7, 2017*

**Algebra 2**

w = x L = (x+1) H = (x-4) w L H = 84 so x(x+1)(x-4) = 84 but the easy way is to look at the answers listed 7 is one bigger than 6 4 is one bigger than 3 so it must be one of the last two if x = W = 6 L=7 H=6-4 = 2 that works if x =W= 4 L = 5 etc, does not work so 2,6,7 works (...

*January 7, 2017*

**Physics**

Fe 7.87 g/cm^3 Ag 10.5 g/cm^3 Viron* 7.87 + Vag*10.5 = 30 Viron + Vag = 20.4 ok?

*January 7, 2017*

**Physicsthe weight on e**

Our spring scales would not work on the moon correctly. We would have to multiply the measurement in grams or kilograms by 6 to get the right answer :) On the other hand a balance scale would work fine.

*January 7, 2017*

**Physics**

This is the second question in a row which confused mass and weight or force. Are you using the same old physics book I wonder?

*January 7, 2017*

**Physics**

well, 250*0.85 = 212.5 cm^3 so it displaces 212.5 grams of water assuming water has density of 1 gram/cm^3 If your book does force in grams, that is the answer. However that 212.5 grams is really the MASS of water displaced. To get the force up you really should multiply that ...

*January 7, 2017*

**Physics**

by the way, what we worked with here was mass, not weight. If this is a Physics course, your book should do mass in kg and weight in Newtons or mass in g and weight in dynes. weight = mass * acceleration of gravity. mass is the same on another planet, weight is different.

*January 7, 2017*

**Physics**

holds 40 g water that is volume = 40 cm^3 since density of water is about 1 g/cm^3 mass = 20 + 40*density of Hg density of Hg = 13.5 g/cm^3 so mass = 20 + 40*13.5 grams

*January 7, 2017*

**Algebra 1**

You are welcome.

*January 7, 2017*

**Algebra 1**

a = b + 2 c b = 2 c so a = 2 c + 2c = 4 c a + b + c = 77 4 c + 2 c + c = 77 7 c = 77 c = 11

*January 7, 2017*

**math**

you could do this by dividing the areas but that is not safe because it might not be exact one way or the other so 6 * 1.5 = 9 8 * 1.5 = 12 6*8 = 48 exactly

*January 7, 2017*

**Math**

4b+2p = 34 p = b-4 4 b + 2(b-4) = 34 4 b + 2 b - 8 = 34 6 b = 42 b = 7

*January 7, 2017*

**algebra**

3 z^2 = -108 z^2 = -36 z = +/-6 sqrt -1 = +/- 6i

*January 7, 2017*

**algebra**

5 x^2 = 651-536 = 115 x^2 = 23 x = +/- sqrt 23 = +/- 4.80

*January 7, 2017*

**Math**

49 - 2v

*January 7, 2017*

**Math**

three choices for the first digit 2 choices for the second 1 choice for the third 3*2*1 = 6 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1

*January 7, 2017*

**algebra**

54 = 2*27 = 2*3*3*3 6 and 9 is 15 so (w-6)(w-9)

*January 7, 2017*

**Calculus**

5[xdy + ydx ] +x^2 dy+y(2x dx)=0 dy(5x +x^2) + dx(5y+2xy) = 0 dy/dx = =(5y+2xy)/(x^2+5x)

*January 6, 2017*

**Chemistry**

Ph determination

*January 6, 2017*

**Chem 111**

1000 kg/m^3 V = pi (d^2/4)h d = 6 ft = 1.83 m h = 17.5 ft = 5.33 m so V = [pi(1.83^2)/4 ]5.33 m^3 mass= 1000 * V in kg there are about 2.2 pounds/kg

*January 6, 2017*

**Math**

(2*27 + n)/3 = 29 54 + n = 87 n = 33

*January 6, 2017*

**Need help with vector questions posted below**

+1 1 3 -1 2 n +2 m 1 determinant = 0 2 + 2n -3m -12 -nm +1 = 0 2n-9 -m(3+n) = 0 m = (2n-9)/(3+n)

*January 6, 2017*

**maths**

everything in thousands two points on line (4,22) and (6,30) (30-22)/(6-4) = slope so slope = m = 4 c = 4 n + b 22 = 16 + b b = 6 so c = 4 n + 6 if n = 4.5 c = 4(4.5) + 6 c = 18+6 c = 24 so 24,000

*January 6, 2017*

**Vectors - Maths [Second Question]**

+1 -1 +2 +1 +2 -4 +m +6 -12 det = 0 -24 +12 +4m -4m +24 -12 = 0 I get any old m

*January 5, 2017*

**Vectors - Maths**

+1 1 3 -1 2 n +2 m 1 determinant = 0 2 + 2n -3m -12 -nm +1 = 0 2n-9 -m(3+n) = 0 m = (2n-9)/(3+n)

*January 5, 2017*

**calculus**

f(x+h) = 1/(2x+2h) f(x) = 1/2x f(x+h)-f(x) = (2x -2x-2h)/2x(2x+2h) = -2h/(4x^2+4xh) divide by h = -2/(4x^2+ 4xh) let h--->0 = -2/4x^2 = -1/2x^2

*January 5, 2017*

**Calculus**

Oh well h = 9 cm r = (6/12)9 = 4.5 cm dV = pi r^2 dh so dV/dt = pi r^2 dh/dt -3 cm^3/min = pi (4.5)^2 dh/dt so dh/dt = -3/[ pi(4.5)^2] about .047 cm/min

*January 5, 2017*

**Calculus**

No. The answer is in cm/min not cm^4/min. I did not check the arithmetic.

*January 5, 2017*

**Calculus**

I and also Steve have answered a million of these. For example: http://www.jiskha.com/display.cgi?id=1415757944

*January 5, 2017*

**incomplete**

earned how much in a year, call it x percent = 100 (x/9000)

*January 5, 2017*

**Maths**

By the way for small angles most of us assume sin theta = tan theta = angle in radians where angle in radians = angle in degrees * pi/180 then the arc length = chord length = R theta

*January 5, 2017*

**Maths**

LOL, If you really want to do it as an isoceles triangle with equal legs of length 5.06 e13 miles then sin .5 minutes = (x/2)/5.06e13 x = 5.06 e13 * 2 sin .5 min sin .5 min = sin (.5/60) degrees = .000145441 times 10.12 e13 = .00147186292 e13 = 1.47 e10 again:)

*January 5, 2017*

**my typo**

found error so your arc length in light years is 2 pi(8.611)/(60*360) = .0025048 light years which is 1.47e10 miles (those are land, not nautical miles) To get it go to Google and type .0025048 light years = miles and hit enter or use calculator and speed of light.

*January 5, 2017*

**Maths**

Clearly parallax is not a problem at this distance :)

*January 5, 2017*

**Maths**

You are right, I have an arithmetic error I estimate that 8.6 light years ia about 5.06 * 10^13 or 5.06e13 miles one minute is 1/21,600 of the circumference [ that is 1/(360*60) because 360 degree and 60 minutes per degree] circumference = 2 pi r = 2 pi * 5.06e13 = about 31 ...

*January 5, 2017*

**Maths**

for that pesky e notation: http://www.mathsisfun.com/numbers/scientific-notation.html look at example at the end: Example: 3.12E4 is the same as 3.12 × 104 3.12E4 = 3.12 × 10 × 10 × 10 × 10 = 31,200

*January 5, 2017*

**Maths**

Oh my, you really need another bit of spherical trig, namely the measure of an angle in "radians" there are 2 pi radians in a circle of 360 degrees so the circumference is C = 2 pi radians * R the handy thing is for any angle in radians now arc length along circle = ...

*January 5, 2017*

**Maths**

2*1.5 = 3 m^2

*January 5, 2017*

**physics (mechanics)**

dU = work done=potential change or force dr = dU U = A/r dU/dr = F = -A/r^2 Sign of A depends on attractive or repulsive.

*January 5, 2017*

**Pre Calc**

These are straight lines, they cross once. 2.4 +.3 t = 1.1 + .7 t .4 t = 1.3 t = 13/4 = 3 1/4 years

*January 4, 2017*

**Math**

pre tax = 1.18 p 1.18 p * 1.06 = 37.20 so p = 37.20 / (1.18*1.06)

*January 4, 2017*

**math - calculus help!**

oh well, not that hard V = (1/3)pi r^2 h r = 7 h/24 so V = (1/3)pi (7/24)^2 h^3 dV/dh = pi (7/24)^2 h^2 dh when h = 10 dV = pi (70/24)^2 dh dV = pi (35/12)^2 dh

*January 4, 2017*

**math - calculus help!**

You could use a fancy formula for volume of a cone and differentiate it to find dV/dh but if you just draw a picture you can see that the area of the surface * dh is the added volume for added dh

*January 4, 2017*

**math - calculus help!**

radius/depth = 7/24 what is radius when depth = 10? 7/24 = r/10 r = 70/24 = 35/12 now the change of volume with depth h is the surface area area * dh = dV pi r^2 dh = dV pi r^2 dh/dt = dV/dt = 12 ft^3/m pi (35/12)^2 dh/dt = 12 dh/dt = .449 ft/min

*January 4, 2017*

**Pre calc**

Good, you have two different ways now :)

*January 4, 2017*

**Pre calc**

slope = (20-13)/(4-3) = 7 also for any (x,y) slope = (y-20)/(x-4) so 7 = (y-20)/(x-4) 7 x - 28 = y - 20 so y = 7 x -8

*January 4, 2017*