Monday

September 26, 2016
Total # Posts: 11,475

**physics**

Question says "using Earth data as a starting point" but does not give the radius of the earth. It could be 6371km (from Google) or any other value with different accuracies. So you will decide which value to use, you just have to state the source.

*November 24, 2014*

**physics**

Assuming the mass distribution and average density of the super-Earth does not depart from our planet, then the radius will be increased by a factor of 10^(1/3)=2.154 approximately. Use whatever radius of Earth that is given to you or you can find.

*November 24, 2014*

**trig**

I guess we all started at the same time, and I am the slowest of us all! :)

*November 24, 2014*

**trig**

1. 4cos(x)-2=0 cos(x)=1/2 x=acos(x)=1/2 between 0 and 2π or π/3 or 5π/3 because cosine is positive in the first and fourth quadrants. 2. 3sec²(x)-4=0 3sec²(x)=4 cos²(x)=3/4 cos(x)=±(√3)/2 for cos(x)=+(√3)/2 x=π/6, 11π/6 cos(x...

*November 24, 2014*

**chemistry**

Ksp=[Pb]³[AsO4]²

*November 24, 2014*

**MATH**

It's not clear who received 9 pennies. Assuming Danni received 9 pennies, Carl got 9*3=27 pennies from Bev. Therefore Bev got 3*27=81 pennies from Al. Al had collected 81*3=243 pennies.

*November 24, 2014*

**business math**

I am not familiar with the rules of the contribution. My interpretation of the question tells me that the taxes are based on the total gross employee income, which comes to (14*640+3*720)*13 weeks (approx. unless leap year) = $ 144560 Based on the given tax rates, the taxes ...

*November 24, 2014*

**Math**

Correct! Use sine rule to solve for the value of sin(B)=0.7825 which translates to 51.5 or 128.5°.

*November 24, 2014*

**statistics - question incomplete**

question incomplete

*November 24, 2014*

**Physics**

(a) use conservation of momentum, note that after collision, there is a common velocity v1=v2=v m1u1+m2u2=m1v1+m2v2=(m1+m2)v m1,m2=masses of bullet and block u1,u2=initial velocities of bullet & block v1,v2=(common) velocity of bullet and block after collision. substituting ...

*November 23, 2014*

**Physics**

ω(t)=t³+2t rad/s note that ω(0)=0 rad/s. (A) Angular displacement =∫ω(t)dt [0≤t≤T] =[t^4/4+t^2] from 0 to T =T^4/4 + T² (B) The angular acceleration is obtained by differentiation of ω(t) with respect to t.

*November 23, 2014*

**physics please help**

Start with the conservation of energy (when friction/air resistance are absent). Kinetic Energy, KE = (1/2)mv² Potential Energy, PE = mgh m=mass, v=velocity, h=change in height, g=acceleration due to gravity. Conservation of energy states that without external forces and ...

*November 23, 2014*

**physics please help**

Angle of ramp, θ=tan-1(2/12) Minimum force required (without friction), F = 65(9.8)sin(θ). Friction force, f= 50N Efficiency = useful force / total force = F/(F+f)

*November 23, 2014*

**math,trigonometry**

Draw a diagram to show the height of the tower (36m), angle of depression (from horizontal)=25°. So tan(25°)=36÷width Solve for wideth.

*November 23, 2014*

**Statistics**

When μ and σ are known, the sample mean (x̄) has normal distribution so the statistic is Z=(x̄-μ)/(σ/sqrt(n)), where n=sample size=148. (a) Assuming a symmetrical confidence interval, we have α=0.003/2=0.0015. Looking up a normal probability...

*November 23, 2014*

**Probability**

If the three events are independent, then the probability of getting two given characteristics is the product of the probability of the individual events. Thus P(I∪N)=P(I)*P(N) (if I and N are independent) =(0.10*0.50)=0.05. Note: this probability may include those who are...

*November 23, 2014*

**Physics**

Momentum = mass*velocity Note that velocity is signed. Using subscript 1=before impact subscript 2=after impact. Here, mass=0.118 kg=m1=m2 v1=+3.14 m/s (towards bat) v2=-33.7 m/s (away from bat) Calculate the change in momentum, Δmomentum = m2v2-m1v1 and give answer in ...

*November 23, 2014*

**statistics**

As in your previous question, if we assume random arrival, all students have equal probability of arriving first. The probability of a female student arriving first is given by #of favourable outcomes ÷ total # of possible events.

*November 23, 2014*

**statistics**

Total number of students: 9+15+8+12=44 Total number of females: 15+12=27 The selection is random, so all students have equal probability of being selected. So the probability of selecting a female is 27/44. Convert to a fraction and round to the nearest hundredth (i.e. two ...

*November 23, 2014*

**algebra**

Let c=current speed, and b=boat speed in still water. Speed with current = 225/5=45 mph Speed against current = 225/9=25 mph, Set up equations: b+c=45 b-c=25 Solve for b and c. By the way, when you know the sum and difference of two variables, the variable with the larger ...

*November 23, 2014*

**algebra**

The equilibrium price is where the two lines meet, namely when the number of units the manufacturer is willing to sell equals the number of units the retailer is willing to buy, both at price p. So 20p-1500=x=-4p+900 Solve for p to get p=100 (and x=500)

*November 23, 2014*

**Chemistry**

2Al+Fe2O3 -> Al2O3 + 2Fe Since the coefficients of Al and Fe are both 2, so the amount of iron formed would be in the ratio of the atomic masses, namely 55.85/26.98 (approximatelyly).

*November 23, 2014*

**Physics**

The resultant velocity of two velocities at 90° (such as x and y) apart can be obtained by resultant=sqrt(x-component²+y-component²)

*November 23, 2014*

**physics - insufficient information**

There is not sufficient information to give a numerical answer.

*November 23, 2014*

**Statistics**

This is a case of choosing without replacement, and order does not count. Number of ways = nCr = n!/(r!(n-r)!) =16!/(4!12!)

*November 23, 2014*

**math**

When two planes intersect (such as the edge of a rectangular box), the intersection is a line (not a point). When two planes do not intersect(such a the top and bottom faces of a rectangular box), then they don't intersect at exactly one point.

*September 23, 2014*

**reference frames**

Taking the difference is the right approach. However, they are heading in different directions, so the velocities have different signs. Hope that helps.

*September 23, 2014*

**Math - correction**

Correction: The equation given above σ²=(sum of (xi-μ)²)/N applies to a population. C is correct if we interpret the data as a sample of the given population, in which case the standard deviation is given as: σ²=(sum of (xi-μ)²)/(N-1) = ...

*September 23, 2014*

**Math**

C is not correct. There is a choice which is close to the answer. The previous post shows how you can find the correct answer.

*September 23, 2014*

**Math**

First find the mean, μ where μ = (sum of all numbers, Σxi)/(number of values, N) Standard deviation, σ, is given by σ²=(sum of (xi-μ)²)/N and finally σ=sqrt(σ²)

*September 23, 2014*

**Math**

see other answer. http://www.jiskha.com/display.cgi?id=1411497383

*September 23, 2014*

**Linear Algebra**

Your answer is correct. The fact that t2=0 means that t1 and t3 are linearly dependent, resulting in two independent variables in R3. This is still a linear dependent set.

*September 23, 2014*

**Math**

To check whether a triangle is a right-triangle, add the square of the two shorter sides. If the sum equals the square of the longest side, then it is a right-triangle. Example: Triangle ABC has sides 5,12,13. 5²+12²=169 = 13² therefore the ABC is a right ...

*September 22, 2014*

**math**

A+P=25 P+B=19 B+A=16 Buy one from each deal and you will get 2 apples, 2 pears, and 2 bananas for (25+19+16)=60 pesos. How much would you spend if you buy only one of each?

*September 22, 2014*

**Chemistry**

Answer is correct! Q=mcΔT However, use of the equality sign is valid only when both sides of the sign are equivalent. You could write: Energy required =13g * 1.00 cal/g°C * 2 °C =26 cal

*September 22, 2014*

**math - ratios**

Given: Girls : Boys = 7 : 3 Girls+Boys:Girls-Boys = 10:4 = X:200 where X is the total number of children (Girls+Boys) or 10/4=X/200 Cross multiply to find X=200*10/4 = 500

*September 22, 2014*

**math - correction**

Since going around once reduces the width and length by 4', 9.26'/4'=2.315 Nala would need to mow around the lawn between 2 to 3 times to finish half the work.

*September 21, 2014*

**math**

Total area = 25*45 = 1125 sq.ft. Half of the area = 562.5 sq.ft What is needed is the size of the inside rectangle left, or (25-x)(45-x)=562.5 Solve for x to get x=9.26' and reject the other root which exceeds 25. Since 9.26'/2'=4.63 strips, so Nala has to go ...

*September 21, 2014*

**chem**

Half life = 15h Activity A(t)=A(0)*2^(-t/15) Solve for t in A(t)=5000=80000(2^(-t/15)) to get t=60 (hours)

*September 19, 2014*

**Calculus**

The position function for a free fall from rest is: x(t)=(1/2)gt² In metric units (x in metres, t in seconds), x(t)=(1/2)*(-9.8)t² =(1/2)(-9.8)6.7² =-220 m approx.

*September 19, 2014*

**PHYYYYYSICS 10**

Horizontal component of velocity = 18 m/s Vertical component of velocity, Vf, is given by Vf²=Vi²+2*a*Δx Vi=initial vertical velocity=0 m/s a=acceleration due to gravity=-9.8 m/s² Δx=-41 m Vf=sqrt(0+2(-9.8)(-41))=28.4 m/s (downwards) angle with ...

*September 18, 2014*

**physics**

Assuming the crate moves upwards. The applied force P is upwards whether the crate moves upwards or downwards at a constant velocity. coeff. of kinetic friction, μ = 0.75 angle of incline, θ = 46° (with horizontal) If crate moves upwards with a constant velocity, ...

*September 17, 2014*

**Mechanism and Machines**

It's surprising that your teacher did not mention any application when the subject was being taught. The linkage essentially converts rotational motion into a straight line movement. The rotational motion usually comes from a motor, and the straight line movement can be ...

*September 17, 2014*

**math - fractions**

Father does the work in x hours, or father does 1/x of the work in one hour. Son does 1/(2x) of the work in one hour. Together, they do 1/x+1/(2x)=1/6 of the work in one hour. 2/(2x)+1/(2x)=1/6 3/(2x)=1/6 Cross multiply 2x=18, x=9 So father does the wok in 9 hours.

*September 16, 2014*

**Math**

Profit = 0 is break even. So solve for x in P(x)=-37x²+1073x-7548 = 0 to give x=12 or x=17 The profit is given by the maximum of the P(x) function, which is located at x=(12+17)/2=15.5, or the maximum profit is P(15.5). (substitute 15.5 for x and evaluate the profit).

*September 16, 2014*

**Math - ratio**

Use ratio / cross multiplication 18:162 ≡ 36:x x=162*36/18 = 324

*September 16, 2014*

**math-fractions**

Total (in fraction) = 1 Woodwinds = 1-2/5-1/3=(15-6-5)/15=4/15 half of woodwinds (4/15) are clarinets, so clarinets = (4/15)÷2= 2/15 One eighth of brass are tubas, so tubas = (2/5)÷8 = (2/40)=1/20 whole : 240 1/20 : x (number of tubas) x=240*(1/20)÷1 =240/...

*September 16, 2014*

**math-addition**

Both Minnie and Amanda have 11 cds, so they have the same number of cds.

*September 16, 2014*

**Physics - kinematics**

Given Vi=36 m/s θ=30 Vix=36cos(30)=31.18 m/s Viy=36sin(30)=18 m/s Vy(t)=Viy*t+(1/2)gt² =18*1+(1/2)(-9.8)*1² =13.1 m/s velocity=sqrt(Vix²+Vi(1)²) =sqrt(31.18^2+13.1^2) =33.82 m/s

*September 16, 2014*

**Math - compound interest**

i=4% p.a. compounded quarterly = 1% per period Let R=(1+i), n= number of quarters/periods Future value FV=100(1+R+R²+R³....+R^(n-1) ) =100(R^n-1)/(R-1) =100(R^n-1)/i For FV=10000 we have 10000=100(R^n-1)/i R^n=(10000/100)*i-1 =2 n=log(2)/log(1.01)=69.66 It will take ...

*September 15, 2014*

**French**

You can also say (formally) "De quel pays êtes-vous venu/venus/venue/venues?" depending on the gender and number of persons to whom you're addressing.

*September 15, 2014*

**trigonometry**

Sorry, don't know if you have used Word or other word processors to write the equation, but they do not translate corectly. Here most HTML symbols are recognized, or you could use ^2 to mean square, and sqrt( ) to mean square-root, etc. Also please write the appropriate ...

*September 15, 2014*

**chemistry**

Solubility is defined as the number of grams of solute that will saturate 100 grams of solvent at a given temperature. So at 20 degrees, we know that the solubility of CuSO4 is 25. Mass of water (solvent)=80 g Use ratios: 25:100 = x:80 Solve for x to get x=25*80/100=20g

*September 15, 2014*

**Algebra**

slope intercept form is in the form y=ax+b If you start from the equation above, you would isolate (solve for) y in terms of x and the constants, then simplify the right-hand side to remove parentheses. Isolate y means use algebraic operations to leave only y on the left-hand ...

*September 15, 2014*

**math**

Probability of rolling two even numbers = (1/2)(1/2)=1/4 Expected value of the game, E(x) is the sum of the following: outcome X, probability P(X), X*P(X) 2 evens=+$8, 1/4, +$2 at least one odd=-$2, 3/4, -$3/2 The sum of X*P(X) = $0.50 The expected value is thus $0.50 for each...

*September 15, 2014*

**computer science**

Command interpreter is a system where it would execute a command at a time, according to the command the user types in. The turtle graphics window is much the same as a command interpreter, except that the command are simpler (turn, move, etc.) and it displays a graphics ...

*September 15, 2014*

**real analysis**

Correction: Somewhere the -8 was inadvertently written as -7, so after corrections, |Xn|≤|-8|+|-1/(n+1)| ∀n∈N or |Xn|≤9 (or M=9)

*September 14, 2014*

**real analysis**

Try and improve on the following. R=set of all real numbers. N=set of all natural numbers Let Xn=-8+n/(n+1), where X∈R then Xn=-8 + (n+1)/(n+1) - 1/(n+1) =-7 - 1/(n+1) => |Xn|≤|-7|+|1/(n+1)| (triangle inequality) But |1/(n+1)|≤1 ∀n∈N, therefore |Xn|&...

*September 14, 2014*

**COMPUTER SCIENCE**

See response: http://www.jiskha.com/display.cgi?id=1410758490

*September 14, 2014*

**Statistics**

A normal distribution is symmetric and unimodol. Therefore an asymmetric bimodal distribution cannot be normal. But beware: A symmetric and unimodal distribution is not necessarily normal. These are necessary but not sufficient conditions.

*September 14, 2014*

**Physics**

Acceleration = (final velocity - initial velocity)/ time =(0 - 22 m/s ) / 2 s = -11 m/s² The negative sign indicates that it is a deceleration (slowing down).

*September 14, 2014*

**physics**

The police car catches up 2.68 m/s for every elapsed second. So to catch up 25.8 m/s, it will take t=25.8 m/s^2 / 2.68 m/s = 9.63 s Since the speeder travels at a uniform speed of 25.8 m/s, the distance travelled can be calculated by Distance = speed * time.

*September 14, 2014*

**French**

The second question is: "Où sont-ils placés par rapport aux noms?" It means where are they ("les mots soulignés", or what you identified in question 1) placed/located relative to the nouns (noms).

*September 14, 2014*

**French**

It is a good idea to have the complete context of the question which in this case concerns grammar. I suppose you have learned about the different groups, of which groupe nominal (GN) is one. The (GN) consists mainly of the noun (nom) and determinants. Determinants can belong ...

*September 14, 2014*

**engineering mechanics**

Try to doodle a triangle of forces and find that the greatest and least resultants occur when the two forces (x,y) are colinear. When they are additive, we have x+y=17 kN, and when they oppose each other, we have x-y=5 (if x>y). Thus solution of the system of equations ...

*September 14, 2014*

**Physics**

Your work is correct, here's the explanation. In a projectile problem, the horizontal (x) motions are independent of the vertical (y) motions. In the case of a horizontally fired projectile from a given height, the problem is equivalent to a free fall from the given height...

*September 13, 2014*

**engineering science**

It is not clear if 30 degrees is above or below the incline. The following solution assumes the supporting force is above the incline. You can do a similar calculation if it is below. First, draw a free-body diagram. Resolve all forces along (+ downwards) the incline, and ...

*September 13, 2014*

**math**

The usual notation for [x] is the greatest integer that is equal to or less than x. For example, [2.5]=2, [-3.4]=-4, but -[3.4]=-3 because the [ ] function applies to a positive number. The greatest integer not exceeding 3.4 is 3. On the other hand, for [-3.4], the greatest ...

*September 8, 2014*

**statistics**

Sorry, I had a miscount. The number of terms of the expansion of (a+b+c+d)^6 is 84 (not 86).

*September 5, 2014*

**statistics**

This problem is the same as putting 6 items in 4 bins. Different ways of solving this problem would be: 1. enumerate in a systematic way: 0006 0015 0024 0033 ... 6000 and count how many you've come up with. Note that since the children are of different ages, and the gifts ...

*September 5, 2014*

**Computer Science**

Explanation of the pattern follows: ^a specifies the string begins with "a" b\$ specifies that the string ends with "b" d* allows 0 or more embedded d's. (cd+)* requires a "c" to be followed by at least one "d". This can happen 0 or ...

*September 4, 2014*

**Computer Science**

Try my $pat="^ad*(cd+)*b\$" Use this pattern to match strings according to the rules specified. Note that $pat will match a qualifying string, but does not define a string. Hope someone else can answer the second part.

*September 4, 2014*

**math**

Outer perimeter: 4s=4*10'=40' Spacing = 6" = 0.5'/plant Number required = 40'/0.5'/plant = 80 plants Since the perimeter is a closed figure, there is no need to add one "at the end" as in the case of a linear row with two ends.

*September 4, 2014*

**math urgent please**

Don't know if you paraphrased the question, but the question is indeed confusing. First it gave the length of 320 cm and width of 320/2=160 cm. So there is no variable to optimized. Then it talks about maximizing 4 faces, and then jumped to optimizing 3 faces. Finally, it ...

*September 3, 2014*

**calculus - insufficient information**

Unfortunately we cannot see fig 2c unless you describe it or send a link.

*September 3, 2014*

**math**

Since it is not stated in the question, we assume that the unit of f(x) is in feet. There is inconsistency with the two expressions for f(x), namely f(x)=(1/2)x²+(4/5)x, and later f(x)=(1/12)x²+(4/5)x Solving the first. If the second expression is intended, you can ...

*September 3, 2014*

**physics**

Average acceleration =(0-30) m/s ÷ 5 s = -6 m/s² Force = ma = 80 kg * (-6 m/s²) = -480 N (resistive force)

*September 3, 2014*

**math**

correct!

*September 3, 2014*

**Physics**

Stress = force/area 1. stres= 6.5*10^5 dynes / (π(0.3)²/4 cm²) = 9195619 dynes/cm² = 919.6 kPa Young's modulus nor strain cannot be derived from the given information. 2. Stress = force /area 10 kg * 9.8 m/s² ÷ (π0.004²/4 m²) = 7....

*September 3, 2014*

**Chemistry**

Use C1*V1 = C2*V2 For example, to dilute 100 mL of 36M solution to 6M, we put 36M *100 mL = 6M * V2 Solve for V2 = 36M*100mL/6M = 600 mL This means that the 100 mL of 36M solution must be diluted to give a final volume of 600 mL.

*September 2, 2014*

**math**

1. -f is the reflection of f about the x-axis. 2. f(-x)=f(x) => f(x) is even 3. f(-x)=-f(x) => f(x) is odd Good job! :)

*September 2, 2014*

**math**

Sum of squares = p²+(p+5)² =625 Expand p²+p²+10p+25=625 2p²+10p=600 p²+5p-300=0 (p-15)(p+20)=0 p=15 or p=-20, reject negative root The sides of the squares are therefore: p=15 p+5=15+5=20

*September 2, 2014*

**statistics**

A five-number summary represents the following qualifiers: minimum Q1 median Q3 maximum the interval minimum/median represents 50% of the data in the lower half. the interval median/maximum represents 50% of the data in the upper half. the interval Q1/Q3 represents 50% of the ...

*September 2, 2014*

**Precedence rules for the algebra community**

Precedence of operators In simple algebra, there is a set of precedence (priority) of operations that should be respected in order that everyone evaluates mathematical expressions in the same way. Although these rules have been taught in elementary school or junior high school...

*September 2, 2014*

**physics**

Assuming the mass of the object is negligible compared to the mass of the person and the boat, then the speed of the object is 30km/h in addition to the speed of the boat. Using a terrestrial frame of reference, the apparent speed of the object by a stationary observer on the ...

*September 2, 2014*

**proportions**

35' : 0.28 kg x' : 7.2 kg Cross multiply and solve for x x=35' * 7.2 kg / 0.28 kg = 900'

*September 2, 2014*

**college algebra**

typo: N = (x+5)*x²/(x+3) =(x³+5x²)/(x+3)

*September 2, 2014*

**college algebra**

First, observe the rule of operator precedence, i.e. BEDMAS (brackets,exponents, division/multiplication, addition/subtration) in that order. Q1. I suspect the expression should have been written as (x+5)/(x+3) to be interpreted correctly. Based on that, we know that the new ...

*September 2, 2014*

**mathzzz want answer in simple way**

Let x=number of rows, and since number of rows = number of persons per row, we have x*x=3249, or x=sqrt(3249) take out your calculator and find x.

*September 2, 2014*

**math**

Sum of angles of a quadrilateral = 360° sum of the other two (C & D) = 360-150=210 If C : D = 2:3, then C+D=210, C: C+D = 2 : 5 = 84 : 210 C=84, D=210-84=126 The first two angles (A & B) add up to 150, which could be A=100, B=50, or A=75, B=75, etc. Without additional ...

*September 2, 2014*

**Math**

Correct! Well done! :)

*September 2, 2014*

**isu**

mass (m) = density (ρ) * volume (v) = 1.46 g/mL * 59.9 mL = 87.5 g

*September 1, 2014*

**Business Math**

Assuming the investment is placed for exactly one year, then the future value is FV=Principal*(1+i) =2989(1+0.03) = $3078.67

*September 1, 2014*

**math**

markdown: 12% : $1.20 sale price : 100% : X Cross multiply and get sale price, X = 1.2*100%/12%=$100

*September 1, 2014*

**Math**

Probability of getting the first white sock out of 30 socks is 24/30 Probability of getting the second white sock out of the remaining 29 socks is 23/29 Since he needs a pair of white socks, both of the above events (steps) must succeed, for which the probability is the ...

*September 1, 2014*

**physics**

Convert values to consistent units: 66 mi/h = 66 mi/h *5280 ft/mi ÷ 3600 s = 96.8 ft/s similarly 55 mi/h = 80.67 ft/s acceleration = -14 ft/s² Time required=(80.67-96.8)/(-14) = 1.15 s Do not forget to add the reaction time, which could exceed the mechanical ...

*September 1, 2014*

**Statics**

The angles are not precisely specified. It is not clear whether the a-axis makes an angle of -20 (340) with the x-axis, or -160 (200) with the x-axis. Same problem for the force F. Could you specify forces and axes using the following conventions: 1. All angles are measured ...

*September 1, 2014*

**Statics**

So you have three forces, the magnitude and angles of which two are known. You will need to first compile a table of known and unknown values. To avoid confusion, you need to follow these rules for describing forces: 1. All angles are to be measured counter-clockwise from the ...

*September 1, 2014*

**Statics**

A description of the accompanying figure is required. Minimally, the directions of F1 and the magnitude of F2 are required.

*September 1, 2014*

**Statics**

If Pa and Fb are both 305N, then angles aOF and FOb are equal to 38 ° See http://www.twiddla.com/1746657 Since F*cos(38)=305N, F=305N/cos(38). You can work out the orientation of b from the figure.

*September 1, 2014*