# Posts by MathMate

Total # Posts: 11,744

**Physics**

The picture is not complete. Are the two blocks identical (in mass) ? Does block B hang free? If it is, B will descend as A moves up. Draw the free body diagram of each block. Let the tension in string be T. mass of each block = m acceleration due to gravity = g angle of ...

*June 1, 2014*

**biology Please Help**

I am not a biology expert, but here are some mathematical aspects of the problem. If both parents are heterozygous (contains one PKU allele, or Pp), the outcomes are: PP has PKU (probability 1/4) Pp carrier pP carrier pp non-carrier (probability 1/4) Probability of being a ...

*June 1, 2014*

**physics**

Round trip distance is double the earth-moon distance. Speed of light is 3*10^8 m/s. Distance = Speed * time, so Time = Distance /Speed Plug in numbers and calculate time accordingly.

*May 31, 2014*

**Pre-Calculus**

If you mean to find the value of cos(2θ) given cos(θ)=7/13, then use the double angle formula: cos(2θ)=cos²(θ)-sin²(θ) where: sin²(θ) =(1-cos²(θ)) =120/169

*May 31, 2014*

**Statistics**

90+6(80)+10(70)+3(60)+2(50)+3(40)=1670 I'll leave the rest to you.

*May 31, 2014*

**math 1 question!!!!!!**

Put the first number (x) of the ordered pair into the equation and check if y evaluates to the second number (y). For example, for B(8, -98), x=8, y=-98. Check: y=–12x – 3 = -12(8)-3=-96-3=-99, so no, B is not the answer. Try all the other options until you get the ...

*May 31, 2014*

**math**

None of them, unless you mean A.(x,y)--->(x+3,y-2)

*May 31, 2014*

**Physics.**

Start with a free-body diagram (FBD). It solves most statics problems automatically when you isolate the system into individual pieces. Start with the 500g block, mass m1. Normal force=m1g coefficient of friction, μk=0.25 Frictional force = μkm1g Let tension in string, T...

*May 31, 2014*

**Physics**

Centripetal force, same as normal force on the "wall" = mrω² Static friction =μs*N =μsmrω² For the people to be "glued" on the wall, static friction must exceed the weight of the riders due to gravity. Therefore, μsmrω&...

*May 31, 2014*

**intro to computers**

It could be: She does not have admin privileges.

*May 31, 2014*

**Solution and colloids**

I would put H2O and CH3OH are miscible since they are both polar, and hexane and CCl4 as well since they are both non-polar.

*May 31, 2014*

**Chemistry**

Thank you Dr. Bob.

*May 31, 2014*

**Chemistry**

molarity is the number of moles per unit volume (L). 6.25 m means 6.25 moles per L of solution, or per 1221.9 g of solution. Calculate the mass density accordingly.

*May 31, 2014*

**Chemistry**

Mass of 1 L of solution = 1.55 g/mL * 1000 mL/L = 1550 g/L Percentage of H2SO4 by mass = 65% Mass of H2SO4 in 1 L = 1550 g/L * 0.650 = 1007.5 g = 1.01×10³ g approximately.

*May 31, 2014*

**physics**

Sum and difference Man:(15+5)/2=10 Water: (15-5)/2=5

*May 31, 2014*

**physics - circular motion**

Speed=v (in given units) magnitude of velocity of each particle = v direction: opposite Velocity of particle 1: <v cosθ,v sinθ> velocity of particle 2: <-v cosθ -v sinθ> Distance between particles: √(((vcosθ-(-vcosθ))²...

*May 31, 2014*

**physics**

At height 4h/5, KE=h/5 PE=4h/5 Ratio of KE:PE=?

*May 31, 2014*

**Algebra 1-- Explain How to Solve**

I suspect #1 is missing parentheses. If it is a big fraction made up of two small fractions, it would read: 1.((x^2 + 8x)/(x - 2)) / ((3x + 14)/(x - 2)) Remember that parentheses are always there around the numerator and denominator. These questions are solved using factors. ...

*May 31, 2014*

**Physics**

Unless I misunderstood the numbers, the value 45 cm does not match the sequence 80,60,40,20. Please check or clarify.

*May 31, 2014*

**Physic**

Tension, T=2640 N Length of wire, L = 2.6 m frequency, f = 330 Hz length density, μ = to be found Using equation: f = (1/(2L))√(T/μ) Solve for μ (kg/m) Multiply be the length of wire, L to get the mass of the wire.

*May 30, 2014*

**sdfds**

Find n using PV=nRT and multiply by molecular mass. R=8.3144621 J K−1 mol−1 or 0.08205746 L atm K−1 mol−1 depending on the units of pressure used Watch number of significant figures used in calculations (at least 4) and the...

*May 30, 2014*

**Physics**

mass, m = 2.5 kg spring constant, k = 320 N/m compression of spring, Δx = 0.075 m Coefficient of kinetic friction, μk = 0.25 acceleration due to gravity, g = 9.8 m/s² Let initial velocity of block, u =u m/s final velocity of block, v = 0 m/s Work done by block, W...

*May 30, 2014*

**Physics**

(a) KE=(1/2)mv² (b) At maximum height, KE in y-direction = 0, i.e. loss in KE =(1/2)m(v sin(θ))² (c) Maximum height, h equate mgh to loss in KE, or mgh = (1/2)m(v sin(θ))² Solve for h.

*May 30, 2014*

**geometry**

Volume of a sphere =4πr³/3 Volume of hemisphere is half of the above.

*May 30, 2014*

**math problem**

If triangle ABC is right-triangle right angled at B or C, then by the definition of sin(A), it is the opposite side length divided by the hypotenuse.

*May 27, 2014*

**Physics**

See previous post http://www.jiskha.com/display.cgi?id=1401230418

*May 27, 2014*

**Physics**

Solve using momentum. Initial momentum=0, since both astronaut and satellite are stationary with respect to shuttle. Assuming velocity away from shuttle is positive, and m1=mass of astronaut, m2=mass of satellite, then m1v1+m2v2=0 97v1+1100*0.13 Solve for v1 to get v1 = -1100*...

*May 27, 2014*

**Physics**

Solve using momentum m1u1+m2u2=m1v1+m2v2 u=initial speed v=final speed m1,m2 masses Using the ground as reference, m1=69.5 kg m2=0.470 kg u1=u2=2.15 m/s v2=16 m/s m1u1+m2u2=m1v1+m2v2 Solve for v1 to get v1=2.056 m/s approx. B) v2=16+2.15=18.15 Solve similarly to get 2.042 m/s ...

*May 27, 2014*

**algebra/Can you see if I am right**

If you mean conditional probability, meaning P(Face|King), or probability of a face card given it is a king, then start with the definition of conditional probability: P(A|B)=P(A∩B)/P(B) P(Face|King) =P(Face∩King)/P(king) =(4/52)/(4/52) = 1 A king is a face card, that ...

*May 27, 2014*

**physics-force and pressure**

Pressure (pascals) = Force (N) / Area (m²) 700 cm² = 700/10000 m²

*May 27, 2014*

**Math**

A: plot 1 has a smaller range (spread) Interpretations regarding C and D. Plot 2 has a higher grade in all quartiles than plot 1, so class of plot 2 has better scores in general.

*May 26, 2014*

**Algebra**

Probability of not repeating, P(no repeat) =10*26*25*24*9*8*7 / (10^4 * 26^4) Probability repeated =1-P(no repeat)

*May 26, 2014*

**math**

You're welcome! :)

*May 26, 2014*

**math**

R∩P means find the set of members which are in both R and P. You can type the symbol ∩ as follows: & c a p ; but omit all spaces. The other symbol can by typed similarly as: & c u p ; For example, 1 is in both R and P. Can you find the other one?

*May 26, 2014*

**trigonometry**

The hypotenuse of a right triangle, using Pythagoras theorem, is Length of cable =√(200²+85²) feet The angle would be arc tangent(85/200)

*May 26, 2014*

**intermed Algebra**

R=timing, t=years after 1925, for example in 1950 t=25, and so on. The problem you need to solve is R=48.8 s and need to solve for t. 48.8=-0.037t+50.1 Solution : t=35.1 This means by 1925+35.1=1961 (round up), world records will be 48.8 seconds or less.

*May 26, 2014*

**physics**

θ is not defined. It is assumed to be the angle with the horizontal. By finding resultant of two cables at θ with horizontal. W=2Tsin(θ) Solve for T=tension in one of the cables.

*May 26, 2014*

**physics**

Using Newton's second law: F=ma and since F=constant, we have m0a0=m2a2 Knowing that m2/m0=(1-0.11)=0.89 you can solve for a2. Note: it does not seem realistic that an aircraft accelerates horizontally for two hours and continue accelerating!

*May 26, 2014*

**PRECALC QUESTION**

Multiply the matrices on the left-hand side and equate cell by cell with the right to get: the equations 6x=-24 y/2-4x=19 Solve for x and y. The two bottom cells turn out to be -6=-6 and 5=5.

*May 25, 2014*

**college physics**

Centripetal acceleration =v²/r or it varies with the square of the velocity. When acceleration is doubled, the velocity is increased by a factor of √2. This way (√2)²=2.

*May 25, 2014*

**physics**

KE=(1/2)mv² =(1/2)*0.1822*4.6² =1.9276 =1.93 (3 significant figures) To calculate the uncertainty, we do a partial differentiation with respect to m and v, and multiply by the maximum errors of δm=0.00005kg and δv=0.05 m/s. δKE=(1/2)v²δm+...

*May 25, 2014*

**Algebra 2**

Write the equation as y=a cos(b(θ))+k For a max=4,and min=-4, k=0, and a=4, so y=4cos(b(θ))) Period = 2π/b if period = 2π/3, then b=3, and the equation reads: y=4cos(3θ) Pick your choice betwen A and D, unless there is a typo.

*May 25, 2014*

**math**

You may want to check the equation to see if there is a typo. I expect it to read: h=-16t²+v_0 t since the object is thrown straight upwards, while gravity (downwards) is indicated negative. If it is fired straight upwards at an initial speed of 800 ft/s, the initial ...

*May 25, 2014*

**ALGEBRA**

Not counting the mitred joints, you will need 4(13"1/8)=4*13" + 4(1/8)=52"1/2

*May 25, 2014*

**Business Math**

Cash discount practices vary. Some expect full payment within the specified date to qualify for the discount, some will discount the paid amount. I assume the latter given the nature of the question. 3/20 means 3% discount on amount paid within 20 days, and the remainder due ...

*May 25, 2014*

**Algebra 2 - Use parentheses**

The expression as is when evaluated according to the BEDMAS rules would be equal to: sin2θ - cosθ since the division is done before the subtraction. The expression should have been written sin2θ/(1-cosθ) in which case = (1-cos2θ)/(1-cosθ) =(...

*May 25, 2014*

**ALGEBRA**

The y-intercept is the value of y when x=0. (0,2) => y-intercept=2 The x-intercept is the value of x when y=0. (4,0) => x-intercept=4.

*May 25, 2014*

**algebra/can you see if I am on the right track**

You have completed the first part of the correct answer, but you forgot the 3 numerals. So 456730*10^3

*May 25, 2014*

**maths**

By mental calculations: Reverse number by adding 18 means the digits differ by 2, 13,24,35, etc. 13/31 does not work, 4*4+3=19 24/42 does not work either, 6*4+3=27 35/53 4*(5+3)+3=35 works. The pair of numbers would be 35 and 53. By mathematics. Let x and y be the two digits ...

*May 25, 2014*

**physics**

If k is the spring constant in N/m, and if the initial length is the natural (stress length), then energy=work done =(1/2)kx² joules where x=stretching in metres =15.9cm=0.159 m

*May 25, 2014*

**Math functions help**

a) correct b) put (x+1) instead of x in f(x), f(x+1)=1-2(x+1)=1-2x-2=-2-2x c) g o f(x) (reads g of f(x)) means g(f(x)) =g(1-2x) =(1-2x)²+1 =1-4x+4x²+1 =2-4x+4x² =2(1-2x+2x²) d) f-1(x) the inverse of f(x). follow the following steps to find the inverse. 1. ...

*May 25, 2014*

**quadratics math**

Let h=height base, b =h+4 Area of triangle =bh/2 =(h+4)h/2 or h(h+4)/2 = 48 Solve for h. h²+4h-96=0 (h-12)(h+8)=0 h=12 or h=-8 (reject negative root)

*May 25, 2014*

**euclidean geometry-missing diagram**

Please describe diagram or post a link. If ABC form a triangle, and X,Y are mid-points of AB and BC, then mXY = mAC÷2 Reason: ΔBXY~ΔBAC SAS mXY=mAC÷2 corr. sides proportional

*May 25, 2014*

**math quadratic equations**

A. correct B. look for two numbers m,n such that mn=2*15=30, and m+n=13. m and n are therefore 10 and 3. 2x²+10x + 3x+15 =2x(x+5) + 3(x+5) =(2x+3)(x+5) C. y-intercept: correct. X-intercept=zeroes. Factorize y=x²-3x-4=(x+1)(x-4) to get the zeroes. The vertex is ...

*May 25, 2014*

**Physics**

60 rpm = 60 revolutions / minute = 60 revolutions / 60 seconds = 1 revolution / second = 1 hertz (Hz) So what is 45 rpm in Hz? Orbital time is the shortest time for any point on the record to come back to the previous position, which is the same as the time it takes to make ...

*May 25, 2014*

**Physics**

It would be easier to set references. In this case, I would set t=0 when B starts pursuit, at which time A would be ahead by 25 m/s *2 s = 50 m. For distance reference, I would set B's initial position as zero. This means that A's position as a function of time, A(t...

*May 25, 2014*

**7th math**

You need to know the scale. Divide the dimensions by the scale to get the drawing dimension. For example, for a scale of 1:500, 120 m /500 = 0.24 m = 24 cm 400 m /500 = 0.80 m = 80 cm and so on. Familiarity with units conversion is a definite asset in these problems.

*May 25, 2014*

**algebra**

All students have equal probabilities of being picked (random). Number of possible successes (picking an A-student) = 24 Size of Ω (sample space)=237 Probability of success = 24/237, a little more than 10%.

*May 24, 2014*

**PRE CALC HELP PLEASE**

First set up equation for each house to put together a system of 3 linear equations. You can then solve by the method you have learned. Finally post your answer for checking as necessary. I will start the setting up of the equations. Let M=pluMber's hours E=electrician'...

*May 24, 2014*

**maths**

Isolate variable by transposition: 5t²=520 Divide by the coefficient of t² t²=520/5=104 Take square-root on both sides: t=±104=±10.2 (approximately)

*May 24, 2014*

**Algebra**

Hmm... I would think expected profit (oil)=415000-25000=390000 expected profit (gas)=145000-25000=120000

*May 24, 2014*

**Geometry (Checking)**

See your original post.

*May 24, 2014*

**Business mat**

b=3 after you subtract 7x from both sides.

*May 24, 2014*

**algebra**

The question says Find P(A) if P(A)=0.7, so P(A)=0.7 Do you mean P(A')=1-P(A)=1-0.7=0.3?

*May 24, 2014*

**Geometry**

You're welcome!

*May 24, 2014*

**Geometry**

All correct except the first. A point from the inside of a simple figure will cross an odd number of times to connect to any point outside.

*May 24, 2014*

**Maths**

Yes, it makes life a little easier. I love integers! :)

*May 24, 2014*

**Maths**

Let the series be a, ax, ax² "The third term is 3.2 times the sum of the other two" means ax²/(a+ax)=3.2 cross multiply: ax²=3.2(a+ax) cancel common factor a (≠0) & multiply by 10 10x²-32x-32=0 =>x=4 or x= -4/5 Reject solution where |x|<1...

*May 24, 2014*

**Algebra 1 - use parentheses**

According the the BEDMAS rules, the expression you posted simplifies to 25-1-3x-10 =14-3x which is probably not what is intended. All fractions have implicit parentheses on the numerator and denominator. You have probably omitted to insert them when you transcribe the ...

*May 24, 2014*

**Precalculus...repost.. The tutor didn't quite answ**

The tutor was saying plug -7.5 in for x in +16x^2+200x +600=0, which means that -7.5 is indeed a root of -16x^2-200x -600=0. The fallacy lies in the statement: " plugged -7.5 in for x in -16x^2-200x-600 the result does not equal to +600" The result should equal to ...

*May 24, 2014*

**physics**

"Assume the +x-direction is up along the slope and the +y-direction is perpendicular to the slope and out of the ground." Since the perpendicular component of the velocity "digs" into the ground, so by definition of the y-axis, it is negative.

*May 24, 2014*

**physics**

Good catch, didn't see the details!

*May 24, 2014*

**physics**

Let v=ground velocity of plane = 500 m/s Since slope is rise/run, so the angle of the "ground" relative to the horizontal θ=tan<-1>(3/100) Component of velocity vector perpendicular to the ground = v*sin(θ) = ?

*May 24, 2014*

**physics**

See earlier post: http://www.jiskha.com/display.cgi?id=1400921781

*May 24, 2014*

**Algebra**

You're welcome!

*May 24, 2014*

**Algebra**

I guess my typo made more confusion than anything else! :( a1/2 ÷ a² is the mathematical equivalent of a1/2 / a² so no worries. I wrote the ÷ specifically to avoid confusion since two "/" signs were in the expression.

*May 24, 2014*

**Algebra**

a1/2 ÷ a² is the mathematical equivalent of a1/2 / a² so no worries. I wrote the ÷ specifically to avoid confusion since two "/" signs were in the expression.

*May 24, 2014*

**Algebra**

If you mean a1/2 ÷ a² then by the law of exponents, 1/a² becomes a-2 and the expression equals a1/2+(-2) =?

*May 24, 2014*

**bu**

Voltage (volts) = current (amp) * resistance (Ω) or I=V/R (amps) V=220 volts Case 1: each resistance alone, R=24Ω Case 2: in series, R=2*24=48Ω Case 3: in parallel, R=1/(1/24+1/24)=12Ω You can then calculate current I in each case using formula above.

*May 24, 2014*

**physical**

Horizontal range = v²sin2θ/g => solve for v(initial). Kinetic energy after launch = (1/2)mv² Elastic potential energy before launch =(1/2)kx² Equate potential energies before and after launch to find k, the elastic constant of the mechanism.

*May 24, 2014*

**Math - SHM**

Given T seconds =k √L (cm) where k is an arbitrary constant to be determined. Also given 0.63=k√9 Therefore we can determine the constant k. k=0.63/√9=0.21 The relation now reads: T(L)=0.21√L where T is period in seconds and L is length of pendulum in ...

*May 24, 2014*

**Algebra**

Assuming the distance is x miles. Then with tail wind, ground speed=240+40=280 mph against wind, ground speed = 240-40=200 Total time x/280 + x/240 = 6 Solve for x to get the maximum one-way distance.

*May 24, 2014*

**physics**

y-component of any force equals ysin(θ) where θ is the (counterclockwise) angle with the +x-axis. So the y-component of the resultant =ΣFsin(θ) =8sin(30)+8sin(120) =?

*May 24, 2014*

**Consider the graph with V = [A, B, C, X, Y, Z] and**

V is a set of vertices. E is a set of edges (lines joining the vertices) (a) Two distinct vertices are adjacent when there is an edge joining the two. So to list vertices adjacent to Y , we need to go through all the edges and select those that include Y as a vertex. The other...

*May 23, 2014*

**MATH HELP PLEASE!!**

Quoting: "Homework Posting Tips Please show your work. Tutors will not do your homework for you. Please show your work for any question that you are posting. ..."

*May 23, 2014*

**math**

See answer to previous post. This one would be an excellent example for practice.

*May 23, 2014*

**math**

12 gal. ÷ (7/8-1/8) =16 gal. Does not look like a huge tank!

*May 23, 2014*

**french**

"Est-ce que" is a standard phrase to introduce a question without inversion of subject and verb. Similar to "Is it that..."

*May 23, 2014*

**french**

Tu: personal pronoun, second person singular. Fais - second person singular for "do".

*May 23, 2014*

**math**

Domain means a set containing all possible values of the first value of the selected ordered pairs. Can you identify which ordered pairs she chose?

*May 23, 2014*

**maths**

1 rod = 5 1/2 yards = 3*(5 1/2) feet = 33/2 feet So one foot =1/(33/2) rod = 2/33 rod

*May 23, 2014*

**algebra**

P(a)=12.21=14.7*e-0.21a Solve for a: e-0.21a=12.21/14.7 Take log on both sides, log(e(x))=x -0.21a=log(12.21/14.7) a=log(12.21/14.7)/(-0.21) =?

*May 23, 2014*

**Math**

20C4 where nCr=n!/((n-r)!r!)

*May 23, 2014*

**Math**

Do you have a figure to go with it?

*May 23, 2014*

**Maths A level**

Cross sectional area =π(40²) =1600π change in height per unit time =dh/dt =(rate change in volume/cross sectional area) =-32πh^(0.5)/1600π =-0.02h^(0.5) The sign is negative because h decreases with time.

*May 23, 2014*

**Math**

W=wind speed A=air speed Equation are set up using Speed*Time = distance, or Distance/Speed = Time 2800/(A-W)=4 2/3 ...(1) 2800/(A+W)=4 ...(2) Solve system of equations for A and W.

*May 23, 2014*

**Probability**

P(being female | the person earns over $75,000) =P(F∩O)/P(O) =(585/1200)/(1070/1200) =585/1070 P(F)=650/1200 =>P(F∩O)/P(O) ≠ P(F), i.e. P(F∩O) ≠ P(F)*P(O) therefore they are not independent.

*May 22, 2014*

**physics**

G=6.67384 × 10-11 m3 kg-1 s-2 M=4.56*10^24 kg r=7.09*10^6 m Using Newton's law of gravitation, g=Force/1 kg mass =GM/r² m/s²

*May 22, 2014*

**Math**

You're welcome!

*May 22, 2014*

**Math**

An equation is not a function, but a function can be part of an equation. For example, f(x)=0 is an equation, while f(x) is a function. A function is like a black box that churns out values when given an input value or input values.

*May 22, 2014*