Monday

April 20, 2015

April 20, 2015

Total # Posts: 20,912

**physics... PLEASE HELP**

well, it is late but I might be able to point a direction average intensity = average power / (pi r^2) Peak = twice average power if a sine wave [ average of sin^2 = (1/2) ] energy density usually in Joules per square centimeter where it hits I assume per second. That would be...
*October 15, 2014*

**Physics - Second Law Question**

same as the other question (3-1.96)10^5 Newtons up
*October 15, 2014*

**Physics - Second Law Question**

4.9 - 4.5 = 0.4 0.4*10^-3 = 4 * 10^-4 down because weight is bigger than drag up
*October 15, 2014*

**Physics**

NO!! Usually in a given problem the SUM of kinetic and potential energy is more or less constant. I say more or less because energy is easily lost from your nice neat problem through friction or escape of heat or whatever messy thing happens to make your car not coast forever ...
*October 15, 2014*

**Math**

(7/8)hr/(3/4) puzzle = 7/6 hours/puzzle or 6/7 puzzles/hour
*October 15, 2014*

**Pre-Calc/Trig...**

b^2-4ac 5^2 -4(2)(-3) that will be positive and therefore its square root is a real number. Thus two real roots, nothing imaginary about it 1^2 - 4(-1)(1) everything positive again, two real roots
*October 15, 2014*

**Physics**

x momentum after = x momentum before after p = 38 (6.06 cos 10.5) + 2.37 v before p = (38+2.37)(5.07) set equal, solve for v which will probably be negative (kid goes forward, board goes backward)
*October 15, 2014*

**Pre-Calc/Trig...**

4 sqrt -1 = 4i 7 sqrt -1 = 7i
*October 15, 2014*

**Math**

do you mean??? [(-3) ^-4 ] [ 5 ^-2 ]=? if so [1/(-3^4 )] (1/25) (1/81)(1/81)(1/25)
*October 15, 2014*

**Algebra 2**

1+6+11 = 18 = 2/3 of cast so cast = 27 27 - 18 = 9 which is indeed 1/3 of the cast
*October 15, 2014*

**Algebra 2**

cost = c Briana + 73 = c Molly + 65 = c Briana + Molly = c so molly = (c - Briana) now we have Briana + 73 = c (c - Briana) + 65 = c or Briana = 65 Briana + 73 = c 73 + 65 = c = 138
*October 15, 2014*

**Science**

been there, done that http://www.jiskha.com/display.cgi?id=1413411282
*October 15, 2014*

**Mechanics**

x velocity = 15 across y velocity = .9 downstream note order of answers c. time to cross = 500/15 = 33.33 seconds b. downstream y = .9 * 33.33 = 30 meters a. sqrt (.9^2+15^2) angle to x axis = A = tan^-1(.9/15) d. sin^-1 (.9/15) toward upstream e. component of speed across = ...
*October 15, 2014*

**math**

n-2, n, n+2 4(n-2) - n = 12 + 2(n+2) 4 n - 8 - n - 12 - 2n - 4 = 0 n - 24 = 0 n = 24 22 , 24, 26
*October 15, 2014*

**Math**

let z = cos A 4 z^2 - 3 z = 0 z(4z-3) = 0 z = 0 or z = 3/4 so cos A = 0 when z = 90 degrees cos A = 3/4 when z = 41.4 degrees but that is not between 90 and 180
*October 15, 2014*

**Algebra Help**

(2x+5)^.5 - (x+6)^.5 = 1 you mean maybe, parentheses missing if so (2x+5)^.5 = 1 +(x+6)^.5 2x+5 = 1 + 2 (x+6)^.5 + x+6 (x - 2) = 2 (x+6)^.5 x^2 - 4 x + 4 = 4 x + 24 x^2 - 8 x - 20 = 0 (x-10)(x+2) = 0 x = 10 or x = -2 go back and see what works in the original now.
*October 15, 2014*

**algebra**

1. let z = x^2 then yo have 4 z^2 - 4 z + 1 (2z-1)(2z-1) which is (2x^2-1)(2x^2-1) 2. a^2 (a^2+1)
*October 15, 2014*

**algebra**

(x+3)(x-2) 3*5 = 15 which differs from 113 by 2 so (3x-1)(2x+5)
*October 15, 2014*

**Linear Algebra**

.866 is sin 60 by the way
*October 13, 2014*

**Linear Algebra**

L1 = 1 L2 = -.5 - .866 i L3 = -.5 + .866 i eigenvectors messy see http://www.wolframalpha.com/widgets/view.jsp?id=9aa01caf50c9307e9dabe159c9068c41
*October 13, 2014*

**Algebra 2 Answer Check**

just put in a bunch of cost values from 0 to 10 if the cost were $2 change = 8 cost - change = 2 - 8 = -6 and 10 - 2(8) = -6 It is only non-negative if the cost is between 5 and 10
*October 13, 2014*

**Algebra 2 Answer Check**

I misread it cost = 10 - change cost - change = 10 - 2 change
*October 13, 2014*

**Algebra 2 Answer Check**

Huh f(x) = 10 - x
*October 13, 2014*

**Algebra 2**

You are right, there is no solution to #1
*October 13, 2014*

**Algebra 2**

Oh, I see, you are right. no positive divided by -5 could be + 6
*October 13, 2014*

**Algebra 2**

-26/3 is negative 34/3 is positive but they could both be negative anyway
*October 13, 2014*

**Algebra 2**

By the way to graph that parabola y = 5 x^2 - 8 x + 11/3 http://www.wolframalpha.com/input/?i=5+x^2+-+8x+%2B+11%2F3
*October 13, 2014*

**Algebra 2**

1. (|3x -4|)/(-5) = 6 A: no solution ========================= multiply both sides by - 5 , no arrow business because just an equal sign 3 x - 4 = -30 or -3x + 4 = -30 3 x = -26 or -3x = -34 so there are two solutions
*October 13, 2014*

**Algebra 2**

6. |12 - 4x| - 4 > 20 A: x < -3 and x > 9 ============================ 12 -4 x > 24 or -12 + 4x >24 -4x > 12 or 4x > 36 x < -3 or x > 9
*October 13, 2014*

**Algebra 2 #1 sorry**

1. (|3x -4|)/(-5) = 6 (|3x -4|) = -30 or 3x-4 = -30 or -3x+4 = -30 so x = -26/3 or x = 34/3
*October 13, 2014*

**Algebra 2**

5. (-3) x (|5x - 8|)- 5 greater than or equal to 6 A: no solution? ============================ 3 (-3) x (|5x - 8|)- 5 >/= 6 (-3) x (|5x - 8|) >/= 11 x (|5x-8)| </= -11/3 x(5x-8) </= -11/3 x(-5x+8) </= -11/33 5 x^2 - 8 x </= -11/3 -5 x^2 + 8 x </= -11/3 ...
*October 13, 2014*

**Algebra 2**

4. [(|x - 2|)/ (4) greater than or equal to 5 A: -18 < x < 22 =========================== x-2 >/=20 or -x+2 >/= 20 x >/= 22 x </= -18
*October 13, 2014*

**Algebra 2**

3. |5x + 15| > 20 A: x > 1 and x < -7 5x +15 > 20 or -5x - 15 >20 x > 1 yes -5x > -35 divide both sides by -5 and reverse the arrow x < 7 why the sign ?????
*October 13, 2014*

**Algebra 2**

2. (|2x -5|) = x + 3 A: x = 8 or x = 2/3 ========================= 2x-5 = x+3 or -2x+5 = x+3 x = 8 or x = 2/3 you got that right. Why did you miss #1 ????
*October 13, 2014*

**Algebra 2**

1. (|3x -4|)/(-5) = 6 (|3x -4|) = -30 or 3x-6 = -30 or -3x+6 = -30 so x = -24/3 = -8 or x = 12
*October 13, 2014*

**Math**

2 sin T cos T cos T /sinT = 2 cos^2 T
*October 13, 2014*

**algebra**

a circle with radius 10 and center at (7,6) (x-7)^2 + (y-6)^2 = 10^2 = 100 where does it hit the y axis (y=0) ? (x-7)^2 + 36 = 100 (x-7)^2 = 64 (x-7) = +/- 8 x = 7 +/- 8 if x = 7+8 then x = 15 if x = 7-8 then x = -1
*October 12, 2014*

**Physics**

The lighter one had to be going faster. To be at 45 degrees, momentum north = momentum east 2000 v = 3000 (2v/3)
*October 12, 2014*

**Physics 12**

u = 12 cos 42 = 8.92 m/s the whole time Vi = 12 sin 42 = 8.03 v = Vi - 9.81 t h = 9.5 + Vi t - 4.9 t^2 0 = 9.5 + 8.03 t - 4.9 t^2 t = [ -8.03 +/- sqrt (8.03^2-4*-4.9*9.5)]/-9.81 t = [-8.03+/-sqrt(251) ]/-9.81 t = 2.43 s
*October 12, 2014*

**calculus**

a = area = 6 x^2 da/dx = 12 x so da = 12 x dx
*October 12, 2014*

**calculus**

Again? http://www.jiskha.com/display.cgi?id=1413057054
*October 12, 2014*

**Nonsense**

It is true that in obsolete English units H(t) = Hi + Vi t - (1/2)(32) t^2 if Hi = 72 ft and Vi = 0 then H(t) = 72 - 16 t^2 however your next line makes no sense at all. perhaps you mean when is H = -184 ??? then 72 - 16 t^2 = -184 16 t^2 = 256 t^2 = 16 t = 4 seconds
*October 12, 2014*

**Calculus**

dv = surface area * dh so dv/dt = surface area * dh/dt width at surface = 40 + (80-40)(30/40) = 40 + 30 = 70 cm = 0.70 m so surface area = 9 * .7 = 6.3 m^2 so .3 m^3/min = 6.3 m^2 * dh/dt and dh/dt = .047 meters/min or 4.7 cm/min
*October 12, 2014*

**physics**

time 2 = 1.81 * time 1 h = (1/2)gt^2 so h/t^2 = constant = H1/t1^2 = H2/t2^2 H2/H1 = t2^2/t1^2 = 1.81^2 = 3.27
*October 12, 2014*

**College Algebra**

Yes, but it is trivial p = 0 and p = 10 give R = 0
*October 12, 2014*

**physics**

m g down ramp = m g sin 28 mg normal = m g cos 28 m g sin 28 - mu m g cos 28 = m (.98) sin 28 - mu cos 28 = .98/9.81
*October 12, 2014*

**physics**

potential energy proportional to height, m g H so Hn = (1-.0534)Hn-1 Hfinal = .9466^n Hinitial 2.79 = .9466^n 5.89 .9466^n = .4737 n log .9466 = log .4737 n = 13.6 so 13
*October 12, 2014*

**calculus**

well Diagonal = D = x sqrt 2 so dD = sqrt 2 dx a = x^2 so da = 2 x dx etc
*October 11, 2014*

**physics**

horizontal force exerted = 75 cos 22 +75 cos 32 vertical force exerted = 75 (sin 32 -sin22) normal force on ground = m g - 75(sin32-sin22) friction force = mu (normal force) acceleration = 0 so friction force = horizontal force exerted work done = 13 * friction force You did ...
*October 11, 2014*

**Math**

.12/52 = .002308 so for n weeks 3 = 1.002308^n log 3 = n log 1.002308 n = 476 weeks or 9.16 years
*October 11, 2014*

**Calculus**

v = x^3 729 = 9^3 so x = 9 dv = 3 x^2 dx = 243 dx = 849.285 - 729 etc
*October 11, 2014*

**Calculus**

Hint: http://www.jiskha.com/display.cgi?id=1413053733
*October 11, 2014*

**Trigonometry**

Hint: sin 2a = 2 sin a cos a so what is 3 sin 2a?
*October 11, 2014*

**calculus**

surface area = a = 6 x^2 da/dx = 12 x so if a = 24, x = 2 da = 12 x dx = 12*2 * dx = 24 dx if da = 2.016 then dx = da/24 = .084 (answer part 1) volume = v = x^3 = 8 when x = 2 so dv/dx = 3 x^2 dv = 3 (2^2)(.084) (part b) 100 (dv / v)
*October 11, 2014*

**Education 606**

http://davidmlane.com/hyperstat/z_table.html
*October 10, 2014*

**physicss**

v = Vi + a t Vi = 0 a = -10 so v = -10 t 0 = 1980 + 0 t - (1/2)(10)t^2 5 t^2 = 1980 t = 19.9 seconds so v = -199 m/s
*October 10, 2014*

**equation**

1 1/2 = 3/2 (3/2) / 3 = 3/6 = 1/2
*October 10, 2014*

**equation**

4/3 ---- 3 is 4/9
*October 10, 2014*

**Math**

bobpursley is correct but of the answers listed B is correct. Your course evidently does not do significant figures. yet.
*October 10, 2014*

**Math**

yes
*October 10, 2014*

**Physics**

we do not have your figure.
*October 10, 2014*

**calculus**

series for f(x when a = 0: tan x = tan 0 + sec^2 0 (x) + .... = 0 + 1 x ..... when does x = tan x +/- .1 make a table of x in radians vs tan x
*October 10, 2014*

**Algebra- please help answer**

5 815/1000 6 21/1000 --------------- 11 836/1000 = 11 418/500 = 11 209/250 11.836
*October 9, 2014*

**Algebra**

.75 + .125 + .09 = .965 1.2 - .965 = .235
*October 9, 2014*

**Algebra whoops !**

11 209/250
*October 9, 2014*

**Algebra**

11 836/1000 = 11 209/1000
*October 9, 2014*

**physics**

2*10/d^2 = 4*10/(12-d)^2
*October 9, 2014*

**physics**

component of weight down ramp = 600 sin 30 = 300 pounds
*October 8, 2014*

**No idea**

I have no idea what your jockey experiment is.
*October 8, 2014*

**physics**

http://science.howstuffworks.com/transport/engines-equipment/pulley.htm
*October 8, 2014*

**Physics**

Pulling with component up on block reducing the normal force between block and floor and thus reducing friction force which is maximum of coefficient of friction times normal force.
*October 8, 2014*

**math**

I do not understand. There are only four aces in the pack. If order is not important, then there is only one way.
*October 8, 2014*

**math**

combination of 4 jacks 3 at a time C(4,3) = 4! /[ 3! (4-3)! ] = 4 combination of 4 twos 2 at a time c(4,2) = 4! /[2!(4-2)!] = 3 so 4*3 = 12
*October 8, 2014*

**Math! Please check!**

You are welcome, good luck.
*October 7, 2014*

**Math! Please check!**

Got it ?
*October 7, 2014*

**Math! Please check!**

Yes and yes To remember forever: 1. Hypothesis: If cow , then mammal 2. converse: If mammal,then cow (maybe) 3. inverse: If not cow, then not mammal (maybe) 4. contrapositive: If not mammal, then not cow (true) Make Venn diagrams for the situation :)
*October 7, 2014*

**Math**

http://davidmlane.com/hyperstat/z_table.html
*October 7, 2014*

**math**

(5/4) *120 = 5 * 30 = 150 pennies which is $1.50
*October 7, 2014*

**math(fractions)**

but 90/20 is 9/2 which is 4 1/2 which is 4.5
*October 7, 2014*

**Algebra**

It is going to be ten times as big.
*October 7, 2014*

**Algebra**

how many 125s in 8450 ? 8450 ----- = 67.6 so 67 full rows 125
*October 7, 2014*

**Algebra**

well, we sure seem to be into division :) 384,400 -------- = 110.587 so 111 3476 because .587 is more than half way from 110 to 111
*October 7, 2014*

**Math! Please check!**

I agree with all of your choices.
*October 7, 2014*

**physics**

v = Vi + a t 152 = 0 + 1.35 * 10^4 t but 1.35 * 10^4 = 135 * 10^2 t = (152/135) * 10^-2 = 1.13 * 10^-2 = .0113 seconds
*October 7, 2014*

**What pulley system**

I have no idea what your block and tackle looks like so can not calculate the mechanical advantage. Divide 1000 by the number of parts of the line pulling up on the piano.
*October 7, 2014*

**PHY1015S**

Two of them :)
*October 7, 2014*

**Math**

if you do not know calculus area of surface = pi d^2/4 area of surface * change in height/min = volume/minute pi d^2/4 * .24 m/min = pump rate - leak rate
*October 5, 2014*

**Math**

0.16 c = 4 so c = 4/0.16 = 25 then yes, subtract 4 and get 21
*October 5, 2014*

**Confusing increase in percent**

That is always confusing and the thing to remember is that doubling is 100% increase.
*October 5, 2014*

**Math**

If the result is 400% of the original 100%, then the increase is 300% +100% = doubled +200% = tripled +300% = quadrupled
*October 5, 2014*

**Physics gr. 12**

You went about this correctly. I did not check the arithmetic.
*October 5, 2014*

**Math**

+++++++ 2 x___+ 1_______ 5x-6 / 10 x^2 - 7 x - 6 ++++++ 10 x^2 -12 x +++++++++++++++ 5 x - 6 +++++++++++++++ 5 x - 6 Remainder = 0
*October 5, 2014*

**math**

at t = 0 xA = -20 , dxA/dt = -24 yA = 0, dyA/dt = 0 xB = 0, dxB/dt=0 yB = 0 , dyB/dt = 25 Dx = differnce in x location = 20 + 24 t Dy = difference in y location = 25 t distance = (Dx^2+Dy^2)^.5 distance = [ 400+480t+576t^2+ 625t^2 ]^.5 = [1201 t^2 + 480 t + 400 ]^.5 d distance...
*October 5, 2014*

**solve long divison polynomials**

http://www.jiskha.com/display.cgi?id=1412542641
*October 5, 2014*

**probability;math**

By the way, they were trying to trick you. If the Jack were NOT replaced, there would only be 51 cards when you went to pick the 8. Then it WOULD HAVE BEEN 4/52 * 4/51
*October 5, 2014*

**probability;math**

as long as it is replaced, the events are independent 4/52 * 4/52
*October 5, 2014*

**Physics**

v = Vi + a t Vend = 24 + 35 (1.9) angle at 1.9 s = 1.9(Vi+Vend)/2 total angle = 436 + angle at 1.9 s time at Vend = 1.9 + 436/Vend
*October 5, 2014*

**Math Growth Rate w/ inflation**

1.5 = (1+r)^3 log 1.5 = 3 log (1+r) 1 + r = 1.1447 r = .145 so 14.5 percent 1.08 = 1.1447^n find n continuous 1.5 = e^3k ln .5 = 3 k
*October 3, 2014*

**Physics**

4.92/360 = 500/c c = 36,585 km approximate check a degree on a great circle (around any circumference) of earth is 60 nautical miles :) (1.852 kilometers / naut mile) 360 * 1.852 * 60 = 40,000 close enough
*October 3, 2014*

**Math**

3.647 - 3.003 = 0.644 = 0.6
*October 3, 2014*