Saturday

August 27, 2016
Total # Posts: 1,219

**Math**

x (.20) + (300 - x)(.40) = 300 (.28) .2 x + 120 - .4 x = 84
*July 27, 2016*

**physics**

the rock reaches its peak after 12/g s it ascends at an average rate of ... (12 m/s + 0 m/s) / 2 it then free falls from h m g h = ½ m v² ... v = √(2 g h) t = 2 h / v
*July 27, 2016*

**Physics**

a * [1 - (p / density of Hg)]
*July 27, 2016*

**algebra**

(s + 7)² = s² + 189 s² + 14 s + 49 = s² + 189 14 s = 140
*July 27, 2016*

**maths**

h(x) = 2 - x g(x) = x²
*July 27, 2016*

**maths**

f(x) = g[h(x)] g(x) = x³ h(x) = 2x + 1
*July 27, 2016*

**Physics**

the energy stored in the spring is ... ½ k x² ... this energy is K.E. when the spring is in the neutral position (the middle of its travel) K.E. = ½ m v² ... so the velocity and the amplitude are directly related to each other (both squared) a) velocity...
*July 27, 2016*

**Math**

a) h / 300 = tan(16º) ... h = 300 * tan(16º) b) tan(Θ) = h / (300 - 75)
*July 27, 2016*

**geometry**

the 3rd side must be greater than the difference, and less than the sum, of the 1st two sides
*July 26, 2016*

**Math**

[(8 * 60) + 37] * 25 ft
*July 26, 2016*

**physics**

the average velocity is ... 36 m / 2 s = 18 m/s gravity has slowed decelerated) the arrow by ... 9.8 m/s² * 2 s = 19.6 m/s [v + (v - 19.6)] / 2 = 18 ... v = 27.8 m/s (launch velocity) time to peak is ... 27.8 m/s / 9.8 m/s² peak height is ... time to peak * 27.8 / 2 ...
*July 26, 2016*

**Geometry**

after translation ... [(-6 + 3),(-4 + 5)] = (-3,1) after rotation ... (1,3)
*July 26, 2016*

**Maths**

B = 3 J ... J = B/3 B = J + 450 ... B = B/3 + 450 ... 2B/3 = 450 ... B = 450 * 3/2
*July 26, 2016*

**Statistics**

15 is 1.5 above the mean ... this is 1.5/7.3 standard deviations ... .2055 use a z-score table to determine the fraction of the population this represents 15 yr or less ... 58%
*July 26, 2016*

**engineering mechanics**

normal ... m g cos(30º) parallel ... m g sin(30º)
*July 26, 2016*

**math**

1/A + 1/B = 1/8 ... 15/B = 15/8 - 15/A 6/A + 15/B = 1 ... 6/A - 15/A + 15/8 = 8/8 ... -9/A = -7/8 ... -72 = -7A
*July 26, 2016*

**Math**

x (25 - 2x) (32 - 2x) = 1575 expand the cubic equation find a solver online (use google)
*July 25, 2016*

**physics**

10 min = 600 s 600 s (20 m/s + 30 m/s) = 30 km ave spd = 30 km / 20 min = 1.5 km/min 10 km / 20 m/s = 500 s 10 km / 30 m/s = 1000/3 s 20 km / (1500/3 s + 1000/3 s) = ... 60 / 2500 km/s = 36/25 km/min = ... 1.44 km/min
*July 25, 2016*

**CHECK MY ALGEBRA 2**

?????
*July 25, 2016*

**CHECK MY ALGEBRA 2**

a hole is a disruption at a single point ... try [(x - 4) / (x - 4)] ... the division by zero causes the discontinuity, but the equal numerator means no other point is affected f(x) = (x - 4) / [(x - 4) (x + 2)]
*July 25, 2016*

**Physics**

assumptions ... the person does not ride the ice down ... the height of the break is even with the top of the slope the gravitational potential energy of the ice is converted to kinetic energy and then heat by friction the total energy dissipated is ... m g h = 100 kg * g * ...
*July 25, 2016*

**College physics**

this is the Doppler effect (google it) the pitch (frequency) is higher because you are moving toward the source f = [343 / (343 - 5)] * 4000
*July 25, 2016*

**Physics**

Vh = 3 m/s² * 30 s = 90 m/s ½ m Vv² = m g h ... Vv = √(2 g h) = √( 2 * 10 * 80) tan(Θ) = Vv / Vh
*July 25, 2016*

**chemistry**

pH = 14 - pOH pOH = - log[OH⁻] = - -8 = 8
*July 24, 2016*

**Math**

top area???
*July 24, 2016*

**PHYSICS**

acceleration ... d = 30 s * [(20 m/s + 0 m/s) / 2] cruise ... d = 15 s * 20 m/s deceleration ... d = 5 s * [(20 m/s + 0 m/s) / 2] add the three distances
*July 24, 2016*

**math: permutations**

couple in 1st row ... 2 ways for 1st row ... 4! ways for 2nd row couple in 2nd row ... 4*5 ways for 1st row ... 4! ways for 2nd row [(4 * 5) + 2] * 4!
*July 24, 2016*

**math:age**

2 s = u 3 (s - 9) = u 3 s - 27 = 2 s
*July 23, 2016*

**Help me anyone - Pre-Calc**

Θ is in radians 20º = (2 π / 18) rad 2340 = ½ (2 π / 18) r² 18 * 2340 / π = r²
*July 23, 2016*

**math**

e = p + 50 time = distance / rate ... 1.6 (1800 / e) = 1800 / p substituting ... 1.6 [1800 / (p + 50)] = 1800 / p solve for p, then substitute back to find e and the times
*July 23, 2016*

**Calculus - Differentials**

the error (in D) is ±.05 A = π D² dA = 2 π D dD = .6 π same difference...
*July 23, 2016*

**Calculus**

h = height up wall d = distance from wall by Pythagoras... h² + d² = 20² differentiating ... 2 h dh/dt + 2 d dd/dt = 0 substituting ... (2 * h * -3) + (2 * d * 4) = 0 ... 8 d = 6 h ... d = ¾ h h² + (¾ h)² = 400 solve for h substitute back...
*July 23, 2016*

**physics**

[16 * cos(20º)] / 4.9 the values in the problem are to 2 significant figures ... not sure about hundredths accuracy
*July 21, 2016*

**Science **

I can be traced back to 3000bc, often go unnoticed, can be overhead, under feet or somewhere in between, evolution has changed me, am lighter than I used to be, and can protect your investment.
*July 21, 2016*

**Physics**

distance = 70 * 5 = 350 km speed = distance / time = 350 / (5 + 2)
*July 21, 2016*

**Math**

3, 5, 9, 15
*July 20, 2016*

**Physics**

N is to the left google "right hand SOLENOID rule"
*July 20, 2016*

**chemistry**

(3 / 2) * 41.0
*July 20, 2016*

**Math**

if r = -2, then the denominator is zero...a big no-no factor the numerator and go with B
*July 20, 2016*

**Chemistry**

1.63 is [SO₂]² ... take the square root
*July 20, 2016*

**Physics**

heat capacity is proportional to mass mass is proportional to volume volume is proportional to the cube of the radius heat cap. ratio is ... 1³:2³
*July 20, 2016*

**Physics**

(a) 2400 + 1800 (b) 1800 / (2400 + 1800)
*July 20, 2016*

**math**

h = 4 mi * tan(5º) = 4 * 5280 ft * tan(5º)
*July 19, 2016*

**Math**

the area of the real world room is (36 / 2.5)² times the area of the plan
*July 19, 2016*

**Physics**

the velocity is half, so the remaining energy (kinetic) is a quarter of the original 3/4 of the energy to penetrate 15 cm it will penetrate another 5 cm
*July 19, 2016*

**Science**

m g h = ½ m v² h = v² / (2 g) h = ½ g t² ... v² / (2 g) = ½ g t² t = v / g .. this is ½ the flight time
*July 19, 2016*

**Math**

6000 = 2500 (1 + r/4)^(10 * 4) 2.4 = (1 + r/4)^40 log(2.4) = 40 log(1 + r/4) .0095053 = log(1 + r/4) 1.002213 = 1 + r/4
*July 19, 2016*

**physics**

the expansion coefficient is ... α = 1.20E-5 m /m·ºK ΔL = 1.20E-5 * 12.5 * (154 - 5) L = 12.500 + ΔL
*July 18, 2016*

**Physics**

energy (work) = 1/2 k x^2 w = 1/2 * 950 N/m * (.06 m)^2
*July 18, 2016*

**Math**

multiplying by 1/3 ... (1/x) / [x^(-2/3)] = 1 / [x^(1/3)] multiplying by x^(-2/3) ... 1/x = [x^(-2/3)] / [x^(1/3)] ... = 1 / [x^(3/3)] = 1/x
*July 18, 2016*

**physics**

units conversion a = v / t d = Vave / t = 30 mph / 3.2 s
*July 18, 2016*

**Physics**

average velocity is ... (.36 + 0) / 2 t = d / v = .8 m / .18 m/s acceleration ... a = .36 m/s / t f = 80 kg * a
*July 18, 2016*

**Math**

f - s = 28 2.5 (f + s) = 2320 f + s = 928 adding equations to eliminate s ... 2 f = 956
*July 17, 2016*

**chemistry**

He⁺ because the greater charge of the nucleus keeps a "tighter" hold on the electron
*July 16, 2016*

**physic**

you need the coefficient of friction to solve this
*July 16, 2016*

**physic**

g = 32.2 ft/s (a) 3.73 * 32.2 = w (lbs) (b) 3.73 * (32.2 + 5.5) = w (c) same as (a) (d) 3.73 * (32.2 - 5.5) = w
*July 16, 2016*

**General Physics**

integration is the correct approach work (energy) = F(x) dx the force goes to zero at √2.6, and then goes negative ... this is also the point of max energy
*July 15, 2016*

**Algebra 2**

they appear to be the same line (colinear)
*July 15, 2016*

**math 101**

145 is one s.d. above the mean 68% of scores are in this range 34% are above the mean 50% of scores are below the mean that leaves 16% of scores above 145
*July 15, 2016*

**maths**

good solution, Steve
*July 15, 2016*

**maths**

actually, slope-intercept is better
*July 15, 2016*

**maths**

find the equations (point-slope) of the diagonals and set them equal
*July 15, 2016*

**math ratios**

1 + 6 = 7 7 k = 21 ... k = 3 3 water and 18 fertiliser
*July 15, 2016*

**Physics**

m g h = .12 J .012 * 9.8 * h = .12
*July 14, 2016*

**physics**

the average speed is 40 m/s so it takes 25 s to cover the km the acceleration is 3.2 m/s² ... 80 m/s / 25 s speed halfway 500 = ½ * 3.2 * t² ... find t and multiply by the acceleration to find the speed half speed 40 m/s / 3.2 m/s² = 12.5 s ...average ...
*July 14, 2016*

**Math**

the Richter scale is logarithmic 10^(8.8 - 5.3)
*July 14, 2016*

**physics**

it takes the 1st stone 2 s to reach its peak and return to the top of the tower, now going downward with the same velocity as the 2nd stone that velocity is 9.8 m/s when it reaches the ground, its velocity is 39.2 m/s...4 s * 9.8 m/s its average velocity is 24.5 m/s ... (9.8...
*July 14, 2016*

**science**

.001 moles / .5 L = .002 M
*July 14, 2016*

**science**

λ =330 m/s / 1E4 cycles/s = 33 mm
*July 14, 2016*

**physics**

the average speed is 10.0 m/s ... 70.0 m / 7.00 s 1st point speed is 5.00 m/s ... 10 = (15 + 5) / 2 acceleration is (10.0 m/s / 7.00 s)
*July 13, 2016*

**Science**

mass * [heat of vaporization + (specific heat * temp change)]
*July 13, 2016*

**Chemistry**

a mole of ANY gas occupies 22.4 L at stp (5.2 / 22.4) * Avogadro's number
*July 13, 2016*

**Algebra**

(3 / 2s) + (1 / s) = 1 / 9 27/2 + 9 = s = 45/2 b = 2/3 s = 15
*July 13, 2016*

**physics**

combined force is 2 kN each pier acts as a fulcrum in a class 2 lever system 6 m * 2 kn = 10 m * f1 4 m * 2 kn = 10 m * f2
*July 12, 2016*

**math**

f + s = 205 5 f + 15 s = 2025 ... f + 3 s = 405 subtracting equations ... 2 s = 200
*July 11, 2016*

**Physics**

1 / R + 1 / 400 = 5 / R 1 / 400 = 4 / R
*July 11, 2016*

**Chemistry**

a liter of solution has a mass of 1.114 kg 20.0% of that is H₃PO₄ ... 222.8 g the molar mass of H₃PO₄ is ... 97.99 g so the moles/L is ... 222.8 / 97.99 the 20.0 means 3 sig fig
*July 11, 2016*

**Math**

g(x) = -2 (2x - 4)³ - 1
*July 11, 2016*

**Math**

f(x) = (x + a) (x + b)² (x + c)³
*July 11, 2016*

**maths**

2 sin(21º) = cos(69º) sin(29º) = cos(61º) so it's twice sin² + cos²
*July 11, 2016*

**math,maths**

x/x + 2/x ≥ .2 1 + 2/x ≥ .2 2/x ≥ -.8 2 ≥ -.8 x -5/2 ≤ x
*July 10, 2016*

**Math**

the distance is the same 10 (s - 21) = 7 s 10 s - 210 = 7s
*July 10, 2016*

**math**

r + b = 365 ... 10 r + 10 b = 3650 9.5 r + 10 b = 3645 subtracting equations ... .5 r = 5
*July 10, 2016*

**Pre-Calculus 11**

squaring ... 9 - 6x + x² = x² - 5 x = 7/3
*July 10, 2016*

**math**

L = w + 5 w * (w + 5) = 500 w² + 5 w - 500 = 0 factoring ... (w + 25) (w - 20) = 0 w = 20 ... L = 25
*July 9, 2016*

**Physics**

heat = mass * temperature change * specific heat for the water heat = 200 g * 7.2 ºC * 1 cal/gºC heat gained by the water is the heat lost by the metal for metal heat = 95 g * 70.8 ºC * s.h. s.h. = (water heat) / (95 * 70.8) be aware of significant figures in ...
*July 9, 2016*

**Algebra**

ln(y) + 5 ln(y+1)
*July 9, 2016*

**physics**

each of the four sides of the square is 5 Ω diagonally, there are two parallel paths of two 5 Ω resistances in series each path is 10 Ω (5 + 5), and the two paths in parallel results in a net resistance of 5 Ω
*July 8, 2016*

**physics**

a hanging spring with a freely hanging mass the force (from gravity) is ... m * g = .98 N k = F / d = .98 N / .01 m = 98 N/m
*July 7, 2016*

**PHYSICS**

multiplying or dividing ...add the percent uncertainties 16 ± 2.25% the cm are cancelled in the division process...it's just a ratio
*July 7, 2016*

**Algebra**

squaring both sides ... 36 = n^(2x) multiplying by n ... 36 n = n^(2x + 1)
*July 6, 2016*

**Algebra**

the drop time is ... t = 132 ft/s / 32 ft/s² it starts from rest, so the average velocity is ... (0 + 132) / 2 ft/s the distance is ... d = drop time * average velocity
*July 6, 2016*

**Science**

going directly from a solid to a gas is called sublimation
*July 6, 2016*

**Physics**

heat = mass * temp change * specific heat make sure the units are consistent
*July 6, 2016*

**Calculus**

the horizontal components of the two ropes' tensions balance each other the combined vertical components equal 400 N sin(60º) = T1v / 400 N T2v = 400 N - T1v cos(60º) = T1h = T2H T2 = √[(T2v)² + (T2h)²]
*July 6, 2016*

**Chemistry**

the iron is oxidized the hydrogen is reduced
*July 6, 2016*

**Physics**

80 C / .001 s = 80000 C/s = 80 kA
*July 6, 2016*

**Math (Quadratic Equations)**

(1 / A) + (1 / B) = 1 / 12 (1 / A) + [1 / (A - 7)] = 1 / 12 12 A - 84 + 12 A = A * (A - 7) 24 A - 84 = A² - 7 A 0 = A² - 31 A + 84 factor the quadratic to find A
*July 6, 2016*

**Math**

-3 is not a root the roots are ... -3±i 4, -3+i, -3-i
*July 6, 2016*

**Math**

the highest exponent is the order...and the number of roots a root is a value that makes the function equal to zero you can test values for roots ... 4 works here divide the function by (x - 4) to factor out the known root ... this leaves a quadratic ... use the quadratic ...
*July 6, 2016*