Saturday
July 4, 2015

Posts by MathMate


Total # Posts: 11,301

Physics
Mass of water that escapes per unit time = m Since the mass of water drops in height by an equivalent of h=1.14 m, we can equate change in energy = 0, or mgh-(1/2)mv^2=0 Solve for v
April 9, 2015

Physic
Power for resistors in series = V²/(R1+R2) Power for resistors in parallel = V²/(1/(1/R1+1/R2)) = V²*(1/R1+1/R2) Solve for R2.
April 9, 2015

Physic
Power = V²/r watts so resistance for the 75W bulb R1 = 120²/75 Ω = 192 Ω Similarly calculate R2 for the 25W bulb. Net resistance of two resistors in parallel R = 1/(1/R1+1/R2)
April 9, 2015

physics
Without air resistance, time to drop to ground (irrespective of horizontal velocity) t = √(2gh) horizontal distance = horiz. velocity * t
April 9, 2015

Mechnical principles
Archimedes principle: Buoyant force on a submerged or floating object is equal to the weight of fluid displaced. Volume of metal = volume of fluid displaced = weight of fluid displaced / density of fluid = (buoyant force) / density of fluid = (500-446) g / 1000 g/L = 54 mL ...
April 9, 2015

Math.
1-4 are correct. For #5, interest = 1200*0.045*2=108 principal = 1200 Total to repay = 1200+108=1308.
April 9, 2015

Math help
Yes, B is correct, here's how: 3.36/6=(3+0.3+0.06)/6=3.00/6+0.30/6+0.06/6
April 8, 2015

mat
4.5% compounded monthly is i=0.045/12=0.00375 per month. n=38 months Present value, Pv=125 Future value, Fv = Pv(1+i)^n
April 8, 2015

statistics
4***5***6***7***8***9***10 If your studying time is a total of 6 hours between 4 and 10 pm. Time left after 8 pm is 2 hours. Assuming random checking, probability that study time after 8 would be the time period between 8 and 10 divided by the total possible time from 4 to 10.
April 8, 2015

math-permutation
The four digits are distinct, so there are 4! possible permutations of the digits.
April 8, 2015

algebra
I have not checked or proved, but believe (6,8,10) is the only triplet that is consecutive even. If you would like to search for more triplets, here's a reference to the work of Brahmagupta: "Pythagorean triples[edit] In chapter twelve of his Brahmasphutasiddhanta, ...
April 8, 2015

Physics !
A. you get the idea, but results can be simplified further Since the bulbs are identical each with resistance r, then in series, R=3r, in parallel, 1/R=(1/r+1/r+1/r)=3/r, in other words, R=r/3. B. Current = i, governed by V=iR. For light bulbs in household circuit, V is ...
April 7, 2015

math
Let x=number of mystery books on the shelf then 3x = total number of books on the shelf we are told that x/5<10<x/4 multiply by 20, 4x<200<5x which means that 40<x<50 So the number of mystery books can be any number between 41 and 49. In other words, the ...
April 7, 2015

physics
Energy = mgh h=difference in elevations between floors. The number of steps is irrelevant because it's the total difference in elevations that counts. If m is in kg, g in m/s², and h in metres, the result mgh is in joules.
April 7, 2015

MATH PLZ SOMEONE HELP
Bread costs $2 a loaf. How much would 1 loaf cost? How much would 2 loaves cost? How much would 10 loaves cost? etc. Similarly, Babysit earns $10 an hour. How much for 2 hours? How much for 5 hours? How much for 10 hours? How much for h hours?
April 7, 2015

Physics - impressive
Your posting speed is impressive, at less than 20 second interval for 7 posts. However, your efforts in solving problems is at the other extreme. The more effort you show, the more chance that help will be given in priority. In fact, you are encouraged to post a problem, study...
April 7, 2015

Physics
(a) Total tension = tension due to mass + tension due to acceleration = mg + ma (b) tension at uniform velocity = tension due to mass only = mg
April 7, 2015

Astronomy
It turns out that detecting planets around other stars is by the periodic dimming of the star, caused by the "eclipse" of the star by the planet. A smaller planet will dim the star to a lesser extent, hence either the periodic dimming phenomenon is more difficult to ...
April 7, 2015

NEED HELP PHYSICS!!!
Equate the centripetal force to 6.8g, i.e. mv²r = 6.8mg solve for r. Note that mass of aeroplane cancels out.
April 7, 2015

NEED HELP PHYSICS!!!
At the bottom of the swing, the vine is subject to two forces, gravity force = mg centripetal force = mv^sup2;/r m=mass of Tarzan (kg) g=acceleration due to gravity (9.81 m/s²) v=tangential velocity (m/s) r=radius of circular motion =length of vine (m) At point of rupture...
April 7, 2015

NEED HELP PHYSICS!!!
Centripetal force is the force that maintains an object in a circular motion. This is an external force that acts on the object in the direction of the centre of the circular motion, namely tension of the string in this case. Centripetal force may be calculated using the ...
April 7, 2015

math
By the pigeon hole principle (where each hole houses one car), it is impossible to have 23+34=57 repairs in 50 lifts (cars). So the surplus must go to cars that need both repairs. This is the least number of cars that need both repairs. Assuming that all cars need at least one...
April 7, 2015

physics
v²-u²=2aS v=0 u=-7.5 m/s S=-4.2 m Solve for a=acceleration in m/s² a=7.5²/(-2×4.2) =6.7 m/s²
April 6, 2015

Math
Median is the middle number of a sorted list of data such that there are as many numbers above it as there are below. For example, median of the set of numbers {3,5,7,10,14,18} is 8.5, which is the average of the two middle numbers. The median of {1,4,9,13,16} would be 9, ...
April 6, 2015

French
"adorer" is a transitive verb (meaning it requires a direct object). Based on Missy literal translation can you correct the sentence? Alternatively, you can say simply J'adore ... the warm days....
April 6, 2015

French (if correct translation/grammer)
Indeed, Ms Sue is right. To clarify, could you tell us if the objective of the exercise is to write a literary essay, or is it a translation exercise? In either case, it would be much easier if you would give the original English version, seeing that the text shows evidence of...
April 6, 2015

Physics
The second parachutist must open the parachute at the moment that she catches up with the first, i.e. has fallen the same distance as the first. 1. Establish the time/distance relation of first parachutist. For the first 3 seconds, distance = 0 + 9.8*(3²) = 44.1 m total ...
April 6, 2015

physics
1 revolution=2π radians 1 minute = 60 seconds (a) Angular acceleration = 180 rpm/8 s =22.5 rpm / s = 22.5*(2π) radians/60s /s =3π/4 rad/s² (b) No. of revolutions =average angular speed * time =(0+180)/2 rpm * (8/60) min = 12 revolutions
April 6, 2015

physics
Power = work done / time Work done =mgh =50*9.8*250 =122500 J Time =10*60 s =600 s Power = work done /time =122500/600 J/s = 204.2 W
April 6, 2015

physics
If car is accelerating uniformly, after 10 seconds, the velocity is 30/2=15 m/s. Distance travelled is time * average velocity =10 s × (0+15)/2 = 75 m Or calculate average acceleration a=30 m/s / 20 s =1.5 m/s² Distance =vi t + (1/2) a t² =0(10)+(1/2)(1.5)(10&...
April 6, 2015

Telecommunication 2.
Radio waves are electromagnetic waves and obey the relation v=fλ f=frequency (Hz) λ=wavelength (m.) v=velocity, m/s and in vacuum,equals the speed of light for electromagnetic waves c=3×108 m/s in air, v is slightly less than c. So solve for f in the above ...
April 6, 2015

physics
"KE 1= 1/2*0.002kg*300^2m/s=30 j KE2=0 work " should result in 90 J (and not 30 J), and assuming energy dissipation is uniform, then KE=W=F*d, F=KE/d=90/.05=1800 N which is exactly the answer you got for the second part. Note: units which are proper names (pascals, ...
April 5, 2015

physics
Correct, well-done! :)
April 5, 2015

Chemistry - Stoichiometry
From the equation, find the stoichiometric ratio of HCl and MnCl2 which equals 2. This means that 1 mol of MnCl2 will generate 2 mol of HCl. Using the fact that 1 mol of HCl occupies 22.4 L at STP, you will find how many mol of MnCl2 will be required to make 0.054 L of HCl.
April 5, 2015

maths - cosine rule
Use the cosine rule: c²=a²+b²-2ab cos(C) with a=7, b=15, and included angle C would vary from 0 to 180 degrees. Note that these limits themselves are not valid values, i.e. max>c>min. They represent the sum and difference of the two sides.
April 5, 2015

Math
An equation of a line must include an equal sign, and your answer does not have one. You probably meant y=-4x+10 Recall some properties of a dilation includes 1. conservation of parallelism, ------------------------------ i.e. lines before and after dilation should remain ...
April 4, 2015

math
Almost. It's 800 cubic feet. Units are important in the answers.
April 4, 2015

math
(2, 2 square root 2, and 2 square root 3) means (2, 2√2, 2√3) Square each number: (4, 2²×2, 2²×3) =(4,8,12) Do these numbers make a Pythagorean triplet?
April 4, 2015

geometry
See your later post.
April 4, 2015

linear algebra check
You have u1 and u2 correct. Don't know if you're expected to rationalize the denominator, in which case, u1 would read [(√3)/3,(√3)/3,(√3)/3]...etc. u3 should be [0,....] A good way to check your answer is to verify if u1.u2=0, u1.u3=0, u2.u3=0.
April 4, 2015

Chemistry
Keq can be obtained by substitution of the product concentrations and reactant concentrations in the definition of Keq. If in doubt, read: http://www.horton.ednet.ns.ca/staff/jeffrey/Chem%2012/answerkeysMJeffrey/kineticsandrates/Meaning%20of%20Keq%20page%201.pdf or examples in...
April 4, 2015

accounting
You can solve using the compound interest formula: Fv = Pv * (1+i)^n Fv=future value, to be calculated Pv=Present value ($8000) i=interest per period (6%/2=0.03) n=number of periods (2)
April 3, 2015

chemistry ap
Assuming zinc is in excess. 18 mL of 6.00 M H2SO4 equals 0.108 mol From Zn+H2SO4 -> ZnSO4 + H2 we deduce that 1 mol of H2SO4 produces 1 mol of ZnSO4. So mass of ZnSO4 produced is 0.108 mol, multiplied by the molecular mass of ZnSO4.
April 3, 2015

accounting
Use compound interest formula: Fv=Pv(1+i)^n here Fv=7500 Pv=present value to be calculated i=8%=0.08 (assume compounding annually) n=18 transposing, Pv=Fv/(1+i)^n
April 3, 2015

math discrete
Oops, I didn't do what the question asked. Go with Reiny's solution!
April 3, 2015

math discrete
f(x)=4x³ g(x)=2x h(x)=x² h◦(g◦f) =h◦(g(x²)) =h◦(2(x²)) =h◦(2x²) =4(2x²)³-5 =4(2²x²)³;-5 =4(2^6 x^6)-5 =256x^6-5
April 3, 2015

PHYSICS
You can read the response to the previous post and try to work out the answer.
April 3, 2015

PHYSICS
By the law of floatation, any floating object will displace a mass of fluid equal to its own mass. So a floating object of volume 1 m³ density 400 kg/m³ will displace 400 kg of water, i.e. fraction of immersed object is 0.4, equal to its specific gravity, and ...
April 3, 2015

math - typo?
A cubic foot of water weighs 62.4 pounds. An imperial gallon of water weighs 10 pounds. You used kg all over, so it is not clear whether there is one or more typos in the question. You will need to check the question and make appropriate corrections before your answer can be ...
April 3, 2015

math
First possibility: 10 B = 10 B After that, we can take advantage that 3B weighs as much as 2A, so you can progressive change every 3B for 2A, for example, 7B+2A = 10B 4B+4A = 10B there is one more that I will leave you to finish.
April 2, 2015

Math
All correct except the first: The square of the length ...
April 2, 2015

math
5•4•3 does not equal 40, you probably meant 5*4*2 you can add 5*8*1 If order does not count, I don't see other ways.
April 2, 2015

calc
A vector that is orthogonal to two given vectors is the cross product, namely |i j k| |x1 y1 z1| |x2 y2 z2| which in this case is |i j k| |1 6 1| |1 -9 1| Expanding the determinant, we get the following vector: <6*1+1*9, 1*1-1*1, 1*-9-6*1> <15, 0, -15> which can be...
April 2, 2015

biology
Some cons to think about: 1. Mandatory donation will no longer be a donation, it will be an obligation. 2. What do you think about the individual rights of citizens of Canada. 3. The need may be urgent, but will the organs of ALL Canadians be required?
April 1, 2015

7TH MATH HELP
A translation is defined as: T: (x,y) -> (x+p,y+q) where p and q are given constants. For example: (10,3) -> (10+p, 3+q) = (1,6) 10+p=1 => p=1-10=-9 3+q=6 => q=6-3=3 So we have established that the translation is T: (x,y) -> (x-9, y+3) (note: if p is positive, ...
April 1, 2015

Algebra 2
Expand sin2θ = 2sinθcosθ so sin2θ=-cosθ 2sinθcosθ + cosθ = 0 factoring out cosθ, cosθ(2sinθ+1)=0 cosθ(sinθ+1/2)=0 Using the zero product property, we deduce that cosθ =0 OR sin&theta=-1/2 Solve...
April 1, 2015

Exponential Equations
Direct substitution of equation: Pv=present value Fv=future value Fv=Pv*(1+i)n where i=interest rate per compounding period (assumed year here) n=number of compounding periods (assumed year here). note that 2.75% is equivalent to 0.0275 for i (interest rate). If both Pv and Fv...
April 1, 2015

Physics
The difference of 2.5 minutes per day is assumed to be due to the difference in g at the two locations. If in Cayenne it loses 2.5 minutes per day, it means the period there is longer. To find how g affects the period, we are given the relationship T=k/sqrt(g) where k is a ...
April 1, 2015

precalculus
If you're not getting the correct answer, I suggest you post how you got your incorrect answer so that we will help you find what went wrong. This is the whole purpose of solving problems.
March 31, 2015

chemistry to MathMate
In case you got confused with the units, I underline that the units are the same, namely, nanometre, or nm. You have a tube of length of 5000 nm, and diameter of 1 nm. How many time is the length bigger than the diameter?
March 31, 2015

chemistry to MathMate
5000 nm is correct. How many times as big is 5000 nm (length of tube) compared to 1 nm (diameter of tube)?
March 31, 2015

to CJ
Perhaps it is easier if we go back to the question to make sure we understand information given in the question, and what the question is asking. "Nanotubes are rolled up cylinders of graphite with diameters of about 1nanometer, and lengths in micrometers." The above...
March 31, 2015

links to previous posts
For reference, these are the links to related posts on the same question. http://www.jiskha.com/display.cgi?id=1427844366 http://www.jiskha.com/display.cgi?id=1427822942
March 31, 2015

chemistry to CJ
Also, it would be of big help to you if you would re-read the question and try to understand what is being asked. It is similar to a problem like: If I can buy a candy with one penny (1 cent), how many candies can I buy with $5.00? knowing that 1$ equals 100 cents.
March 31, 2015

chemistry to MathMate
1 metre = 100 cm 5 metres = ? cm
March 31, 2015

Algebra 2
You're welcome!
March 31, 2015

Algebra 2
use the identities tanφ=sinφ/cosφ cotφ=cosφ/sinφ sin²φ+cos²φ=1 tanφ+cotφ =sinφ/cosφ+cosφ/sinφ =(sin²φ+cos²φ)/(sinφcosφ) =1/(sinφcosφ)
March 31, 2015

Chemistry - toCJ
Recall that the original question is: (I) If a nanotube is 5 micrometers long, how many diameters does this represent?
March 31, 2015

Chemistry - to CJ
If the tube is 1 nm in diameter, then veryify that 5 μm = 5*1000 nm = 5000 nm = how many diameters? Can you tell us what prevents you from finding the answer with the information above?
March 31, 2015

calculus
1. find derivative with respect to h: C'(h) = 1/15-15000000/h² 2. equate C'(h) to zero and solve for h. 2. 1/15-15000000/h² = 0 h²=225000000 h=15000 3. verify that it is a minimum (not maximum) by taking second derivative, and see that C"(15000)>...
March 31, 2015

torque
Torque = force × lever arm Assuming 190 foot-pounds is in gravitational units (i.e. foot-pound wt), then force = 120 pound-wt lever arm = x feet using the torque formula, 190 foot-pound wt = 120 pound-wt * x feet Solve for x (in feet).
March 31, 2015

fluids
use the conversions from 1. pressure: psig (rel) to psi (absolute) by adding 14.69595 psi. 2. temperature: °F to °K by (°F-31)*5/9+273.15 Then use the ideal gas formula: P1 V1 / T1 = P2 V2 / T2 to calculate V2
March 31, 2015

Energy, work, power
12 feet above, below or at the same elevation as the truck? Moving things at the same level is not considered work done because there is no change of potential energy, kinetic energy nor dissipative energy.
March 31, 2015

math
First you need to find the area of an equilateral triangle with side x. Base = x Height = (√3)x/2 Area = (√3)x²/4 Thus, the area as a function of side x A(x)=(√3)x²/4 A'(x) = (√3)x/2 Substitute x=12 cm in A'(x) to get rate of change of...
March 31, 2015

Chemistry
If the tube is 1 nm in diameter, then veryify that 5 μm = 5*1000 nm = 5000 nm = how many diameters?
March 31, 2015

Chemistry
* 1 μm = 1000 nm (nanometer)
March 31, 2015

Chemistry
1m = 1000 mm (millimeter) 1 mm = 1000 μm (micrometer) 1 μ = 1000 nm (nanometer) If the tube is 1 nm in diameter, then veryify that 5 μm = 5*1000 nm = 5000 nm = how many diameters?
March 31, 2015

Physics
Using energy principles, (KE=kinetic energy, PE=gravitational potential energy) KE+PE=constant, so KEi+PEi = KEf+PEf KEi=0 (both are stationary) KEf=(1/2)Iω^2+(1/2)mv^2 PEi=0 PEf=0+mgh (weight descended) Equate energies: 0 = (1/2)Iω^2+(1/2)mv^2 + 0+mgh (note that h...
March 31, 2015

Maths
2/5 of what was left after giving 1/6 to her mother means 2/5 of (1-1/6) of her salary. Working it out: 2/5 × (6/6-1/6) =2/5 × (5/6) =2/6 =1/3
March 31, 2015

Math
Sorry, messed up codes, the iterative equation should read: xn+1=3xn/(xn+1)
March 31, 2015

Math
Fixed points are values of x when the two sides of the iterated map are equal as n->∞. This means that fixed points are essentially the solution of the iterative equation. Here we have: xn+1=3xb/(xn+1) (please check my interpretation of your equation) To find fixed ...
March 31, 2015

physics
75W for 24 hours =0.075 kW for 24 hours =1.8 kW for 1 hour =1.8 kW-h How much would that cost?
March 31, 2015

physics
Gravitational energy (in joules) = mgh where m=mass (k) g=acceleration due to gravity (m/s²) h=height (m) Solve for h.
March 30, 2015

math
No. of digits > 6 : {7,8,9} i.e. 3 of them odd digits: {1,3,5,7,9}, i.e. 5 Total = 3×5 = 15 However, subtract number of plates with identical digits. Figure out which plates there are and calculate the final numbers.
March 30, 2015

Math
IF the size of the cubes is 1 cm³, then the number of cubes is equal to the volume in cm³. If the size of the cubes is bigger than 1cm³, then it is not possible to build the prism with the larger cubes because the GCF of 8,9,5 is 1.
March 30, 2015

Probabilit
4 red out of (4+5+2)=11 marbles Probability that first draw has no red =(11-4)/11 =7 No replacement, so probability for second draw = (10-4)/10 =6/10 Probability that both have no red = product of the two probabilities.
March 30, 2015

math
Hint: Use the triangular inequality, a+b>c where a,b,c represent three sides of any triangle.
March 30, 2015

statistics
Assuming the random selection is from a large pool of people, in which case the probability remains constant throughout the experiment. This experiment could then be modeled by the binomial distribution, with probability P(X=n)=C(N,x)px(1-p)N-x where p=probability of success...
March 30, 2015

Math
Thank you GanonTEK! Indeed, (12/52)(11/51)(10/50) is the correct answer. My bad!
March 30, 2015

Math
Probability =C(52,12) Use your calculator function nCr to calculate C(52,12) where n=52, and r=12. Or calculate =52!/((52-12)!(12!)) =52!/(40!*12!) You need to get familiar with these calculations if you are to learn anything from probabilities.
March 30, 2015

Math
There are four suits in each deck, each with 3 picture cards for a total of 12 picture cards in a deck of 52 (different) cards. The probability of choosing r objects from a pool of n different objects is C(n,r) = n! / ((n-r)!r!) where n!=factorial n = n(n-1)(n-2)...3.2.1 For ...
March 30, 2015

Math
You have probably learned C(n,r)=n!/((n-r)!r!) is the number of combinations of choosing r objects out of n. So in general, if we have letters a,a,a, b,b, c,c,c,c there are C(3,1) ways to choose a letter a C(2,1) ways to choose a letter b and C(4,1) ways to choose a letter c ...
March 30, 2015

French
In general, you have done reasonable work, because you seem to catch the sense of the text. Here are some hints to help you in future exercises and to correct the present text. One good way to do these problems is to translating mentally and reading it aloud to check if it ...
March 30, 2015

Chemistry
Assuming the temperature remains constant, you can use Boyle's law, which says that PV=constant (at constant temperature) or P1*V1 = P2*V2
March 29, 2015

Chemistry
Convert 15°C to °K: 15°C = 15+273.15°K = 288°K Then use the ideal gas equation PV=nRT n=number of moles (constant in this case) R=constant Assume also that P=pressure constant, we have V1/T1 = V2/T2 Solve for T2 to get T2=V2*(T1/V1) Substitute initial ...
March 29, 2015

physics
To prevent sliding, friction must provide (i.e. equal) the centripetal force μmg=mv²/r Solve for μ, with v=25 m/s r=220 m g=9.8 m/s² m cancels
March 28, 2015

Quadratic equations
f(x) is a quadratic equation for which exact solutions may be obtained in many ways, including factoring, completing the square, and quadratic formula. Are you studying numerical methods where an approximate solution is required instead of an exact one? Yes, your answer is ...
March 28, 2015

French Grammar
The sentences are correct or as corrected. But if you are working on, or have learned the demonstrative pronouns celui/celle/ceux/celles, then you can apply them to avoid repeating the subject in the same sentence. For example, the first sentence could have been replaced by: &...
March 28, 2015

statistic
Let's work on this together. 1. How many questions does he need to guess right to pass the test? (include all possible values) 2. What kind of distribution does this problem fall into?
March 28, 2015

math
Right, there was a typo! Thought I corrected it. Thanks Steve! Should read: g*62+(75-g)*56=75*58
March 27, 2015

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