Thursday
November 27, 2014

Posts by MathMate


Total # Posts: 10,821

solid mechanics
If I am not mistaken, tangential stress on a plane section at 60° to the longitudinal axis would be the shear stress, γ, and the normal stress on the same plane is the normal stress, σ. σx=250 kN / (0.1²) m² =25 MPa σy=0 α=60° ...
July 25, 2013

Linear Equations in Two Variables
The answer to this question is any point (x,y) which lies on the lien. To find points that lie on the line, substitute any finite value of x, and evaluate y. Present the answer as a coordinate pair (x,y). For example, let x=1, y=2x-3=2(1)-3=-1 So (1,-1) is a point on the line...
July 23, 2013

To Debela Duguma
Your question tucked at the end of another post was probably lost. Post the complete question as a new post if you would like help.
July 23, 2013

statistics
xBar > 50 => {49+61, 49+62, 61+62} => P(xBar>50)=3/7C2=3/28 xBar>60 => {61+62} => P(xBar>60)=1/7C2=1/28
July 22, 2013

physics
There are lots of assumptions made in this question. In reality, there is a temperature gradient between the outer part of the egg and the (yolk) in the middle, which means that the inner part of the egg is always cooler than the outer part. This gradient diminishes with time...
July 22, 2013

statistic
a numerical value for a correlation coefficient can never be greater than one or less than minus one.
July 22, 2013

Gen physics
μmg≥m|a| => |a|≤μg = 0.632g
July 22, 2013

Dynamics
gradient = rise/run = 0.06 At 1m/s (horizontal distance), the bike and the rider (mass=80 kg) gains potential energy of mgh = 80*9.81*(1m/s * 0.06) = 47.88 W Therefore speed (in the horizontal direction) = 200/47.88 m/s (horiz.) = 4.2474 m/s (horiz.) = 4.2474*(1.0018) m/s (on ...
July 22, 2013

dynamics
Sum work done and energies. Frictional force = F N Stopping Distance = D = 5 m Speed uphill = v = 6 m/s before braking: KE=(1/2)mv^2 PE=0 W=0 after braking: KE=0 PE=mg*Dsin(θ) W=D*F Equate KE+PE+W before and after braking, and solve for F.
July 22, 2013

Data Structures and Algorithms
If the question asks for the last digits, you could code and evaluate the recursive formula to get the results. If you would like a check, you are welcome. The sum of the 3 last digits is 20.
July 22, 2013

Physics
mass of horse = mass of water displaced (Archimedes principle) = 0.027*4.2*6.5 m^3 * 1000 kg/m^3 = 737.1 kg Weight of horse = mg = 737.1 * 9.81 N = 7230 N
July 21, 2013

Calculus
given f(x)=2√x Therefore f(1)=2*√1=2, which means that (x0,y0)=(1,2) is a point on the curve (given). Find f'(x)=(d/dx)2√x=1/√x the tangent at (1,2) is the line passing through (1,2) with a slope equal to it's slope, namely f'(1). Thus the ...
July 21, 2013

physics
Some reading will help you understand the subject, and also help you solve other problems faster. Read, for example: http://en.wikipedia.org/wiki/Total_internal_reflection
July 21, 2013

Incomplete
I hope you realize that incomplete questions are either not answered or will be put on hold until all information is supplied.
July 21, 2013

Physics :)
You're welcome!
July 21, 2013

Physics
Equate kinetic and potential (spring) energies: KE=(1/2)mv² PE=(1/2)ks² Solve for k k=mv²/s² N/m (verify that quantities are in consistent units).
July 21, 2013

physics
The same question has been answered twice before. See http://www.jiskha.com/display.cgi?id=1374277875
July 21, 2013

MATH
Move the decimal point of both numbers 2 places to the left to get 6.0288 divided by 2. Now divide each digit successively by 2 to get 3.0144.
July 21, 2013

Math :)
You're welcome!
July 21, 2013

Math
Divide 57 by 9 to get 6 with remainder of 3 (check: 9*6=54, 54+3=57) So the mixed number is 6 3/9 = 6 1/3
July 21, 2013

math
Lateral surface of a cylinder Al=2πr*h where h is measured along the axis of the cylinder. When the rectangle is rotated along it's length, then h=length, r=width. When the rectangle is rotated along it's width, then h=width, r=lengh. So you can calculate the ...
July 21, 2013

Math<Please Help>
Simple way: Multiply the planar area (25m*12m) by the average depth of (1+4)/2=2.5m to get volume= 750 m³. Calculate the area of the trapezoid which is obtained by cutting a vertical section along the length: 25*(1+4)/2. Multiply the above by the width of 12 m to get the ...
July 21, 2013

Math
Computers actually use binary number systems, since a switch can either be on or off. However, contents of computer memory is more concisely represented by octal and hexadecimal representations because 1. they are easy to convert to and from binary system 2. they are condensed...
July 21, 2013

GCSE Physics
Energy paid for =30/0.15=200 KWH Number of hours for boiler = 200 KWH / power of boiler The number of hours will not be know until the power of the boiler is known.
July 20, 2013

math
Q4c: 1/x^2*x*sqrt(x)*sqrt(sqrt(x))=a^c; 1/x^(1/4) = a^c x=a^(-4c) For: log5(5-4x)=log√5(2-x) log5(5-4x)=log5(2-x)² 5-4x=(2-x)² x=±1
July 20, 2013

physics
Volume of liquid =3.57*10^-4 m^3 =357 ml mass of liquid =357 g mass of aluminium (can) =421-357 =64 g density of aluminium = 2.7 g/ml Volume of aluminium = 64/2.7 cc = 23.7 cc
July 20, 2013

geometry
I am sorry about the incorrect designations. However, the same process can be used to solve for CP=3, although the result would be different. It seems to me that Steve's method is simpler, so use his method. Using Newton's method to solve for a non-linear equation f(x...
July 20, 2013

geometry
First draw the square ABCD and indicate a point P inside the square near the side AB about 1/3 from A to B. Label the lengths AP=1, PB=2, PD=3, and each side of the square s. Join BD and mark the length (√2)s. Label ∠APB as α, ∠DPA as β. Consider each ...
July 20, 2013

Statistics
The following reference may confirm your assumptions. http://cjasn.asnjournals.org/content/3/5/1246.full
July 19, 2013

MAT LAB
For 9_3, the question is not clear because we do not see the accompanying figure. However, on examining the data, it seems probable that the two "walls" (meaning no strain/movement along that direction) are in the y-direction, which means that εy=0. From the ...
July 19, 2013

MAT LAB
Note: Equations (A), (B) and (C) may be used to solve problem 9_2_1, namely Lx=L(1+εx),... Watch the signs of the stresses.
July 19, 2013

MAT LAB
Note that 1/20 is a relatively large strain and the above equations are approximate to first order and may not be accurate for large strains. Use the relations: εx=[σx-ν(σy+σz)]/E ....(A) εy=[σy-ν(&sigmaz;+σx)]/E ....(B) &...
July 19, 2013

MAT LAB
9_1_1 Recall that for an isotropic material, when σx is applied on a material of modulus of elasticity E, then the strains are: εx=σx/E from which e can be calculated. Since εy=-νσx/E, and similarly εz=-νσx/E, we are able ...
July 19, 2013

Calculus
This is a project you need to do using Mathematica. I suggest you go ahead and actually learn to use Mathematica to solve the above problems. If you have doubts and would like to check you results, you are welcome to post them for a check here.
July 19, 2013

math
Yes, 2655 in³.
July 19, 2013

math
Calculate volume of locker V=L*W*H Calculate volume of books (given) B=1545 in³ Calculate volume left =V-B
July 19, 2013

Math
The volume to be integrated is bounded by the planes 0≤x≤2 0≤y≤2 z=0 and the surface z=16-x²-2y². Thus the volume is given by the triple integral: V=∫∫∫z dz dx dy Where z is evaluated from 0 to 16-x²-2y², x and y are both evaluated ...
July 19, 2013

math
The rule for converting from metres to centimetres is that one metre equals 100 centimetres.
July 18, 2013

Solution Set
{x+y=3 ............(1) {-3x+2y=-19 ...........(2) Solve by elimination. Multiply (1) by 3 and add to (2) in order to eliminate x: 3x+3y=9 ..........3(1) -3x+2y=-19 .......(2) Add together 0x+5y=-19+9=-10 Solve for y: y=-10/5 = -2
July 18, 2013

Calculus
If you need help with finding the standard forms of the particular solution, check your course notes, your textbook, or the following link: http://tutorial.math.lamar.edu/Classes/DE/UndeterminedCoefficients.aspx
July 18, 2013

Calculus-ODE
Start with solving for the complementary solution to the homogeneous equation 2y"+3y'+y=0, the characteristic equation is 2r²+3r+1=0 which is an algebraic equation which can be factorized into (2r+1)(r+1)=0 or r={-(1/2), -1} The complementary solution is ...
July 18, 2013

math
Proportions: 100% : 1.75 hours x% : 1 hour x=1*100%/1.75
July 16, 2013

math
Use time = 1/(1/M+1/R)
July 16, 2013

math
2=1/(1/6+1/B) => B=1/(1/2-1/6)=3
July 16, 2013

math
1/(1/20+1/30+1/10) =60/11 minutes
July 16, 2013

math
1/(1/6+1/5.5+1/2.2) =1.245 DAYS
July 16, 2013

algebra
√(75) =√(25*3) =√(5²*3) =5√3
July 16, 2013

math
2³=?
July 16, 2013

gen physics
The centre of gravity is located at a point such that the product of mass multiplied by the distance to the C.G. is equal, namely: Let x = distance from mA, then 50-x = distance from mB. mA*x = mB(50-x) solve for x, and hence 50-x.
July 16, 2013

gen physics
apparent ρ=7860-1000=6860 kg/m² Tension in wire =apparent weight =apparent mass*g =(0.154³)*6860*9.81 N =246 N (approx.)
July 16, 2013

physics
ω2=ω1)+angular acceleration*time or time = (ω2-ω1)/angular acceleration =(0.28-0)/0.021 =40/3 sec.
July 16, 2013

Math
Please comment on the previous answer before reposting: http://www.jiskha.com/display.cgi?id=1373921871
July 16, 2013

math :)
You're welcome. :) The method above is correct, but the final result should be 2 7/24 lbs, since 2*24=48, and 55-48=7. Sorry for the oversight.
July 16, 2013

math - addition of fractions
The question requires us to add three fractions, with different denominators. The first step is to find a common denominator which is the LCM (least common multiple) among 3,4 and 8. Since 4 divides 8, so 4 need not be accounted for. The LCM of 3 and 8 is just the product 24, ...
July 16, 2013

Geomtry
I have a different interpretation of the problem. If I were to assume "three sides" as one length (parallel to the canal) and the two other sides perpendicular to the canal, then we are only fencing three sides on land, and the fourth side is bounded by the canal. ...
July 16, 2013

math
240.75 is correct.
July 16, 2013

Math
From the knowledge of divisibility, we know that 2 is a factor (all even numbers). That reduces 2002=2*1001 Again, the difference of sums of alternate digits equals zero (1+0)-(0+1)=0, so it is divisible by 11. That makes 2002=2*11*91 We should (try to) know all prime ...
July 16, 2013

Math
She cannot subdivide the equilateral triangle into 2 isosceles triangles. This is the smallest N which is impossible. She can subdivide it into 3 congruent isosceles triangles by joining the centroid with each of the vertices. Each triangle is then 30-30-120 as angles. Each of...
July 15, 2013

Calculus
The idea is to find the family of lines perpendicular to L:7x+5y-2=0. Out of that, we find the particular line L1 passing through P(-6,-2). The intersection of L and L1 gives the required point (closest to P). Family of lines perpendicular to L passing through P0(x0,y0): L : ...
July 15, 2013

Statistics
With replacement, the probability of selecting a good apple stays at 60/80=3/4. For a two-step experiment, the probability is the product of individual steps, hence, probability of select a good apple in each pick is (3/4)^2=9/16
July 15, 2013

maths
Two trains with speeds s and s+5 km/hr. Initial distance=340 km final distance = 30 km Total distance travelled = 340-30=310 km Total speed = s+s+5=2s+5 Time = 2 hrs Form equation equating distance travelled Time*speed=distance, or 2(2s+5)=310 2s+5=155 2s=150 s=75 Speeds of ...
July 15, 2013

French
"J'ai faim" is the proper expression to say "I am hungry." Just like in English we would not say "I am hunger", it would be incorrect say the equivalent in French. Another notable difference in French from English is about age. We would say &...
July 15, 2013

object oriented programming
Can you show us your pseudocode as a start?
July 14, 2013

trig
Parentheses are assumed missing. Implied parentheses are ALWAYS required in numerator and denominator of fractions. (cos^2x+sin^2x)/(cot^2x-csc^2x) This problem can be solved by converting all functions in terms of sine and cosine according to the standard definitions. (cos^2x...
July 14, 2013

Java programming- simulation of rolling dice
You have made the arrays die1...die4 to do two things: 1. as a counter (accumulator) for the frequency, and 2. as the value of the face. This is an impossible task, and that explains why the total adds up to more than a million. I suggest you make the following changes: 1. Add...
July 14, 2013

Elementary mechanics
Use the kinematics equation: Vf=Vi+at where Vf=final velocity=i-2j (m/s) Vi=initial velocity, yet unknown a=acceleration=F/m (in vector form) t=time=10 s a=(2i+7j)/5=0.4i + 1.4j Vf=(i-2j)+(0.4i+1.4j)(10) =(i-2j)+(4i+14j) =5i+12j
July 14, 2013

Computers C++
What are your thoughts?
July 14, 2013

GEOMETRY (SA oftriangular pyramid)
In the calculations of surface area of a pyramid, the height is not required if the apothem (slant height) is given. The height is required, however, to calculate the volume of a pyramid. In fact, the height h is not consistent, because h should always be less than the slant ...
July 14, 2013

GEOMETRY (SA oftriangular pyramid)
Lateral surface area =perimeter of base * apothem /2 =3b*s/2 (for a regular pyramid with a triangular base) Area of triangular base with side b =(√3)*b/2*(b/2) =(√3)b²/4
July 14, 2013

math:units conversion
Convert 6 cm to mm = 60 mm. Now add 60mm to 4 mm to get your answer.
July 14, 2013

Math
If each team plays with each of the other four teams N times, then the number of games played would be: 4, 8, 12, ... Can you find which of the five numbers does not belong?
July 13, 2013

College Algebra
Start with (x-(-1/6))(x-(-8/9))=0 Multiply by 54 on both sides to get (6x+1)(9x+8)=0
July 13, 2013

trig
Convert all three functions in terms of sine and cosine, hence simplify.
July 13, 2013

statistics
Possible typo in bold: "Playing game of chance and pay 300 by rolling a fair die one time if you rome a 2 and receive $1300 if you roll a 4 or six you receive $900 if you ore a 3 5 or one receive nothing. find expected value for this game. based on value is it a good game...
July 13, 2013

statistics
Binomial distribution: - large population=>probability is (almost) constant - p=0.5 (men) q=(1-0.5) (women) - random independent multiple trials N=9 - 2 possible outcomes at each trial P(7)=C(9,7)*p^7 * q^2 =(9!/(2!7!))*0.5^7*(1-0.5)^2 =0.07 (approximately)
July 13, 2013

Calculus
See: http://www.jiskha.com/display.cgi?id=1373656357
July 12, 2013

Linear Equation
Let x=number of gallons of regular sold then 220-x=number of gallons of premium sold Total receipt: 2.20x+2.70(220-x)=519 Solve for x.
July 12, 2013

Math :)
You're welcome!
July 12, 2013

Math
x=(5±(√15)*i)/2 If you do not expect complex roots, please check for typos in the original question.
July 12, 2013

Math
x/(x-2) + (2x)/[4-(x^2)] = 5/(x+2) This calls for finding the common denominator, and then solving for x using the numerators. Do not forget to exclude the asymptotes values of x where the denominator becomes zero. LCM (lowest ommon multiple) of denominators (x-2), (4-x²...
July 12, 2013

algebra1 HELP PLEASE Thanks you!!
y=√(64*25)=√(40²)=40 f.p.s.
July 12, 2013

algebra1 HELP PLEASE Thanks you!!
Not sure if there is a typo in your question, the speed is y(x)=5√(x)=5√(25)=25 This corresponding an equivalent acceleration approximately that of Mars.
July 12, 2013

maths
18+0.5+2.5=?
July 12, 2013

maths
The idea is to convert f(x)=asin(x)+bcos(x) into the form g(x)=k*cos(a+φ) where k and φ are constants dependent on a and b. This way, it is easy to show that the max/min values of the f(x) is ±k. Start with expanding g(x) using compound angles. g(x) =k(cos(&phi...
July 12, 2013

Maths
See: http://www.jiskha.com/display.cgi?id=1373620166
July 12, 2013

Math
First find the rule of the parabola: We know that the parabola curves (is open) towards the bottom, so the rule is y(x)=b-ax² if we set the y-axis to cut the vertex. Since y(0)=16=b, so b=16 or y(x)=16-kx² Also, y(4)=0 tells us that k=1, or the rule of the doorway is...
July 11, 2013

alg2 check?
Remember that ^ has higher precedence than * or +, so in these expressions, parentheses are required: 1. (2)(3)x^(1+3) =6x^4 2. (4)^3 x^(1*3) y^(2*3) =64 x^3 y^6
July 11, 2013

Math.
Two step experiment: multiply the probability of each step. A. P(Jeans,t-shirt)=0.3*0.6=0.18 B. P(jeans, ~t-shirt)=0.3*(1-0.6)=0.12
July 11, 2013

Math- important!!!
Use binomial distribution, p=0.28, q=(1-0.28)=0.72 A) n=5 P(3/5)+P(4/5)+P(5/5) =3C5*p^3*q^2 + 4C5*p^4*q^1 + 5C5*p^5*q^0 =10(0.28^3)(0.72^2) + 5(0.28^4)(0.72) + 1(0.28^5)(0.72^0) Use your calculator to find the answer for (A) B) Expected value for binomial distribution with n=...
July 11, 2013

physics
150 * 2*3600 j + 250 * 10*60 j =1230000 j =1.23 Mj
July 10, 2013

differential calculus
Intuitively, the circle has a bigger area for the same circumference, so we try to make a bigger circle. Also, since the area increases as the square of the circumference, we want to make 1 single shape as opposed to two. So intuitive answer is to make the smallest square ...
July 10, 2013

French
Each country name has a gender and a number. The country France is feminine singular, as demonstrated by the phrase "Vive la France!" The country United States (Les États-Unis) is masculine plural. For feminine country names, we use the preposition "en&...
July 9, 2013

math
The question does not give the required context. Some countries charge sales tax on labour, and some may not. I believe Overhead rate would be added to the labour, meaning that for every $12 paid to the worker, the customer pays $12(labour)+$15(overhead)=27. If sales tax does ...
July 9, 2013

Computer Programming
Your code seems to be in reasonable shape, except that it does not yet implement the algorithm to find the maximum revenue. So the current revenue is 600*50=30,000$ a month. Your program will increase the rent by $40 steps and recalculate the revenue. When the revenue starts ...
July 9, 2013

MATH:( Base systems?!
Divide the number by the base and note the remainder on the right. The digits from bottom to top is the number required. Example: Find 37 to base 5. 37 R 2 (37/5=7 R2) 7 R 2 (7/5=1 R2) 1 So the number is 1225
July 9, 2013

Number and Operations
3,6,9 and 18, since 20/18 also has a remainder of 2.
July 9, 2013

math
The question should have read: There are 35 students in a class who stu dy either art, music or both. 15 study art. Twice as many students who study art study music. COMPLETE THE VENN DIAGRAM TO SHOW. 35 students in all 15 study art 2*15=30 study music so 35-30=5 study only ...
July 9, 2013

Math 17 Synthetic Division
Showing steps of synthetic division requires lining up many numbers vertically, which is impossible to do at this web site. I suggest you refer to examples of sites which can format number displays. Try for example: http://www.purplemath.com/modules/synthdiv.htm
July 9, 2013

GEOMETRY LATERAL AND SURFACE URGENT (PLEASEHELP)
Total surface area of a rectangular box =2(lw+wh+hl) where l,w,h=length, width and height respectively. Total surface area of a cubical box (all sides equal to "a" =6a² Total surface area of a Rectangular prism : see above for rectangular box
July 9, 2013

Math
solid: square pyramid height, h = 15 side of base, s = 5 Area of base, Ab=5^2 area of cross section at height y =Ab*(y/15)^2 Volume (using the general solid integral formula based on Simpson's rule) V=(Area at top + Area at base + 4*area at mid-height)*height/6 =(0+25+4*6....
July 9, 2013

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