Wednesday
October 26, 2016

# Posts by MathMate

Total # Posts: 11,475

Physics
Distance between wave crests, λ = wave length = 2 metres Time complete one wave = period = 60 s / 20 waves = 3 s Frequency f is number of waves per second = (1/3) Hz Speed = f * λ = (1/3)Hz * 2m =2/3 m/s
June 2, 2014

Algebra
Next easiest is by comparison. Solve the quadratic by factoring -3x+5 = x² +2x -45 x²+5x-50=0 (x+10)(x-5)=0 x=5 or x=-10 Substitute x to find corresponding values of y.
June 2, 2014

Algebra
Find the vertex of the parabola by completing the square: h(t)=-16t²+20t+6 =-16(t²-2(5/8)t+25/64)+6+25/4 which means that the vertex is at t=5/8 and it will hit the ground at h(t)=0, or t=3/2 s (rejecting negative root). Maximum is at the vertex, or h(5/8)=49/4 ft.
June 2, 2014

Which one is correct?
Eden is right. Multiplying two numbers with the same base is the same as adding the exponents.
June 2, 2014

Algebra/can you help me
log710 =log(10)/log(7) =1.183294662454939 approximately (use your calculator) I'll leave the other problem for you to practise.
June 2, 2014

physics
Some characters are not properly displayed on my computer, I assume it to be: A particle moves along the x-axis from an initial position xi to a final position xf. Of the following values of xi and xf, which results in a negative displacement? (a) xi = 6 m, xf = 4 m (b) xi = -...
June 2, 2014

Math
The starting number (initial value, or y-intercept) is not subject to the power, so the rule for the function is y=2(3)^x year 0: 2(3)^0 = 2 year 1: 2(3)^1 = 6 year 2: 2(3)^2 = 18 ... year 6: 2(3)^6 = 1458
June 2, 2014

Math
{L,M} is the Ω (sample space) for one single draw. When there are two draws one after another with replacement, the sample space will contain LL LM ML MM
June 2, 2014

Physics
Ignoring air resistance, equate potential and kinetic energies: mgh = (1/2)mv² Cancel m, v=√(2gh) =√(2*9.8*15) = 17.1 m/s
June 2, 2014

science
Please look up a diagram of the parts and then give a try at the answer.
June 2, 2014

geometry
The area can be found by using cross multiplication of elements in a rectangular matrix formed by the coordinates of the 4 (or any number) points. Let P be a 5x2 matrix, where the columns represnt the x and y coordinates. Rows 1 to 4 represent the (x,y) ordered pairs of the 4 ...
June 2, 2014

physics
Gravity acts on bodies of mass m with a force of mg equal to its weight. g is the acceleration due to gravity. The given weight is 10N, so gravity is already included, and the net force acting on the table is 10N.
June 2, 2014

rounding to the nearest meter
51 is the nearest metre, and 51.4 is the nearest tenth of a metre.
June 2, 2014

jill
Future value, F = 5*125000=625000 Interest, i = 6% annually = 0.06 compounding frequency, f = 2 Time, t = 2.5 years Let P = present value then use the compound interest formula F=P(1+i/f)ft Solve for P P=F/(1+i/f)ft =625000/(1+0.06/2)2*2.5 =539130.49 =
June 2, 2014

Kirr
June 1, 2014

jill
Isn't 1500 already the present value? Could you double check to see if there is a typo?
June 1, 2014

physics
Distance = speed * time = (1.25*speed)*((1/1.25)*time) = 25 min./1.25 = 20 minutes
June 1, 2014

helppppp math helppp!
Future value, F Interest, i = 0.045 compounding frequency, f = 12 Time, t = 3.5 years Let P = present value, = 250000 then use the compound interest formula F=P(1+i/f)ft
June 1, 2014

physics
Horizontal component of the normal force.
June 1, 2014

Physics
Use Ek=(1/2)mv² Equate Ek=mgh h=height
June 1, 2014

Physics
Good, so Frictional force = ma = 1kg (-2.5)m/s² = -2.5 N Normal reaction =mg =1kg * 9.8 m/s² =9.8 N Coefficient of kinetic friction = Frictional force / Normal reaction = -2.5 / 9.8 = 0.255 (omit sign).
June 1, 2014

It doesn't sound right when you have a 15 ft. ladder leaning against a wall with the foot of the ladder 36.9 ft away. So you need to recheck your work when it does not look right. The length of the ladder is the hypotenuse of the right triangle. The base of the ladder is ...
June 1, 2014

Math
Work on the left-hand side first: csc60 cot30 tan60 =(1/sin60)(tan60)(tan60) =(1/sin60)(tan²60) =(1/sin60)(sec²60-1) =(2/√3)(2²-1) =2√3 Work on the right-hand side: 2sec²45cos30 =2(2/√2)² (√3)/2 =8/2 (√3)/2 =2√3 Thus...
June 1, 2014

Geometry :)
You're welcome!
June 1, 2014

Geometry
Assuming my interpretation of the word "back" is correct, I said: "... because we usually consider the positive x-axis as going forward" so it would be A.
June 1, 2014

Geometry
A sphere has infinite planes of symmetry, a cube does not. All the given choices (A) to (C) are solids. A polygon is a plane figure. We cannot make a solid out of plane figures. We can make faces of polyhedrons out of plane figures, but that's not what the question is ...
June 1, 2014

Geometry
If you notice that all the coordinates of the image are half the corresponding values in the pre-image, this means that the transformation is a contraction about the origin, with a factor of 0.5.
June 1, 2014

Algebra 1
Slope of segment, a = (y2-y1)/(x2-x1) = (8-4)/(6-2)=1 Mid-point =( (x1+x2)/2, (y1+y2)/2 ) =( (2+6)/2, (4+8)/2 ) = M(4,6) Slope of line perpendicular to segment,a1 = -1/a = -1/(1) =-1 Equation of perpendicular line: (y-y1)=a1(x-x1) y-6 = -1(x-4) or y=-x + 10 Check that it goes ...
June 1, 2014

Math
For every 100 people, there were 40 men 30 women 30 children. Use proportion to figure out the number for 2400 people.
June 1, 2014

Algebra
Sum and difference: (sum+difference)/2 = larger number (sum-difference)/2 = smaller number
June 1, 2014

math
1 foot = 0.3048 m (exactly) so 1 m² = (1/0.3048)² ft². Area of rectangle = 48 m × 24 m = 1152 m² = 1152/0.3048² ft² = 12400.0 ft² (approximately)
June 1, 2014

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

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

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

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

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

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)
May 24, 2014

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