What is Unknowns: Definition and 155 Discussions

The Tomb of the Unknown Soldier is a monument dedicated to deceased U.S. service members whose remains have not been identified. It is located in Arlington National Cemetery in Virginia, United States. The World War I "Unknown" is a recipient of the Medal of Honor, the Victoria Cross, and several other foreign nations' highest service awards. The U.S. Unknowns who were interred are also recipients of the Medal of Honor, presented by U.S. presidents who presided over their funerals. The monument has no officially designated name.

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  1. pellman

    Maxwell eqs: 8 eqs for 6 unknowns - too many eqs?

    I know I really need to understand partial diff eqs better for this, but I don't know what subtopic to look for in a pde text. Maxwell eqs are 2 scalar eqs plus 2 vector eqs (3 components) giving eight total equations, coupled in the 6 components of E(x) and B(x). Why not just 6 equations...
  2. M

    Thermodynamics - Using steam tables to find unknowns

    Homework Statement Determine the temperature, quality, and internal energy of 5 kg of (pure) water in a rigid container of volume 1 m3 at a pressure of 2 bar. Homework Equations PV = nRT (maybe?) quality = nv/(nl + nv) where l = number of moles in liquid phase and v = number of moles in...
  3. J

    HELP Collision question with two unknowns

    A 170g ball is dropped from a height of 2.3m, bounces on a hard floor, and rebounds to a height of 1.8m. The figure shows the impulse received from the floor. What maximum force does the floor exert on the ball...
  4. J

    Exploring the Unknowns of Space Travel

    Universe ?? So in books and pics online, you see the solar system in a single plane, if you want to travel great distances you use other planets gravity to swing you out there. What if we wanted to travel in ANY OTHER direction, could it be done? I heard that its not practical to send manned...
  5. Ƒ

    Three Equations, Three Unknowns.

    Homework Statement But somehow not that simple.. \frac{5xy}{x+y} =6\left. \frac{7yz}{y+z} =10\left. \frac{8zx}{z+x} =15\left. Homework Equations The Attempt at a Solution Tried and failed.
  6. C

    Can More Vectors Than Dimensions Be Linearly Independent?

    Homework Statement prove, if S has m vectors in n dimensions and S is linearly independent, then n>=m Homework Equations The Attempt at a Solution so far I've come up with: there is no combination of vectors in S such that their sum is the zero vector, there exists a vector...
  7. T

    Arithmetic mean of two unknowns in a system of equations

    Homework Statement When finding the arithmetic mean in a system of equations is there any reason why the method that I am using is wrong? Find the arithmetic mean of x and y in the following set of equations Homework Equations 3x + 5y = 65 and 7x + 14y = 175 The Attempt at...
  8. H

    Exploring the Big Bang: Unveiling the Unknowns

    In the most recent theory I have heard, just in the first moments after the Big Bang strange things happened. I heard that there was not four fundamental forces, just one, or superforce. I also heard that the laws of physics did not apply. How long was this time. As from research I have...
  9. S

    Max and min problem with 3 unknowns

    Hi, I have this question for a college assignment. It involves 3 'unknowns' (not 3 variables, since 2 are constants). The main difficulty I am having is inexperience with max and min problems where you cannot fully evalaute the solution. I think I have made a reasonable attempt at a...
  10. E

    Solution Set for 4 Equations in 3 Unknowns

    Homework Statement Determine all possibilities for the solution set (from among infinitely many solutions, a unique solution, or no solution) of the system of linear equations. A system of 4 equations in 3 unknowns Homework Equations None. The Attempt at a Solution This is more of...
  11. M

    Solve 2 Equations 2 Unknowns: Hibbeler Dynamics 12th Ed.

    Homework Statement Ok forgive me as an engineering student but this problem should be easier than it seems. The Problem: It is observed that the skier leaves the ramp A at an angle (Theata=25 degrees) with the horizontal. If he strikes the ground at point B, determine his initial speed,V, and...
  12. S

    Bridge circuit - 5 eqns with 5 unknowns

    Homework Statement The bridge circuit for this problem: http://img52.imageshack.us/img52/7366/bridgecircuit.jpg I have to derive a formula for the equivalent resistance (Req) of the bridge circuit shown in the link.Homework Equations I've been able to come up with the 5 equations with 5...
  13. G

    Solving 4 product equations 4 unknowns

    I ran into this in my research and I'm certain it should be extremely simple, but for some reason I can seem to remember how to do it. If I have a setup such as: a1*b1=c1 a2*b1=c2 a1*b2=c3 a2*b2=c4 And the c's are known values, how do I solve for the a's and b's in terms of c's?
  14. K

    System of 4 equations in 4 unknowns

    Homework Statement 0 = A+B+D 0 = A-B+C 0 = A exp(k) + B exp(-k) + C sin(k) + D cos(k) 0 = A exp(k) - B exp(-k) + C cos(k) - D sin(k) Solve for A, B, C, D in the above system. (k is a positive real number) Homework Equations N/A The Attempt at a Solution 1st equation=> D = -A-B...
  15. T

    Finding final speed with two unknowns (Vf1 & Vf2)

    Homework Statement A ball of mass 0.540 kg moving east (+x direction) with a speed of 3.70 m/s collides head-on with a 0.440 kg ball at rest. If the collision is perfectly elastic, what will be the speed and direction of each ball after the collision? ball originally at rest m/s east...
  16. I

    Help with solving two unknowns simultaneously? (physics)

    A mountain climber, in the process of crossing between two cliffs by a rope, pauses to rest. She weighs 566 N. As the drawing shows, she is closer to the left cliff than to the right cliff, with the result that the tensions in the left and right sides of the rope are not the same. Find the...
  17. L

    Vector components with unknowns, ultimately adding to zero.

    Homework Statement If Avec = (6.00 ihat -8.00 jhat) units, Bvec = (-8.00 ihat + 3.00 jhat) units, and Cvec = (26.0 ihat + 22.0 jhat) units, determine a and b such that a Avec + b Bvec + Cvec= 0. a= b= Homework Equations Avec + Bvec = Rvec Rvec = (Ax + Bx)i-hat + (Ay + By)j-hatThe Attempt at a...
  18. R

    Kinematics: 3 unknowns, find Time.

    SOLVED. Homework Statement angle = 10 degrees delta X = 20 delta Y = -1.5 car goes off a 10 degree ramp and lands at the delta X/delta Y. what is T?Homework Equations delta X = VxoT Vy = Vyo + AyT delta Y = VyoT + (1/2)AyT^2 Vy^2 = Vyo^2 + 2Ay(delta Ymax)The Attempt at a Solution none
  19. R

    Calculating Time and Velocity in a Projectile Motion Problem

    3rd week in AP physics... can't figure this out :'( Homework Statement delta X = 20m delta Y = -1.5m angle = 10 degrees basically, a car goes off a 10 degree ramp and lands 20 meters away and the delta Y is 1.5m... my assumption is that I need to find T first. Homework Equations...
  20. I

    How Far Will a Race Car Travel After Running Out of Gas?

    Homework Statement A race car with the weight of 10 000 kg is traveling at 10.0 m/s when it's gas runs out. How far will this race car travel till it reaches an absolute halt? Homework Equations F=ma v2^2-v1^2=2ad The Attempt at a Solution Fn= 490 000N v2^2-v1^2/2d= a and I...
  21. T

    Solving a system of 2 diffrential equations with 3 unknowns.

    Homework Statement r''-(theta')^2=-g reads: second derivative of r minus the first derivative of theta squared equals negative g 2(r')theta'+(r)theta''=0 reads: 2 times the first derivative of r times the first derivative of theta plus r times the second derivative of theta. both r and...
  22. S

    Several unknowns but only one equation

    I have a query please, if anybody can shed some light, thanks: So from an early age we get this idea of needing one equation for each unknown variable whose unique value we need to discover. Three unknowns? well, need three nonsingular equations: it's a kind of a rule of thumb I guess...
  23. B

    MATLAB Solving Unknowns in MATLAB: Approximation Scheme

    Hi. I need to run through an approximation scheme, and one of the variables in the scheme is unknown, but I know what the final answer should be. I want to calculate the value of the unknown by figuring out what it must be for the approximation to equal the expected result after a significant...
  24. S

    Proving Mutual Unknowns in a Room: Hamiltonian Walks

    Homework Statement There are (m-1)n+1 people in the room. Show that there are at least n people who mutually do not know each other, or there is a person who knows at least n people Homework Equations The Attempt at a Solution I think this has to do with hamiltonian walks...
  25. X

    Elastic collision: Help solving for unknowns

    Is it possible to solve for an elastic collision when vb and v'a are the two unknowns? I have been trying for a few hours to solve for either unknown using the conservation of momentum and the conservation of total kinetic energy equations but have come up with nothing. Can anyone help? mava...
  26. K

    Forces Acting on a Ball: Identifying the Unknowns

    Identify the forces on the ball. Static Friction Weight Normal Force Kinetic Friction Tension Drag I'm sure that there is weight and normal force and that there is not tension. I'm also fairly sure that there is no static friction but I am not sure about drag and kinetic friction. I...
  27. B

    What Speed is Required for a Half-Court Jump Shot in Basketball?

    A basketball player tries to make a half-court jump shot, releasing the ball at the height of the basket. Assuming that the ball is launched at 54.0°, 14.0 m from the basket, what speed must the player give the ball? There are a lot of unknowns and i don't know where to start any help?
  28. V

    How to find Fa .to find other unknowns ?

    [SOLVED] how to find Fa...to find other unknowns...? Homework Statement A mountain bike with mass 13.5 kg , with a rider having mass 63.5 kg, traveling at 32 km/h when the rider applies the brakes, locking the wheels. How far does the bike travel before coming to a stop if the coefficient...
  29. O

    MATLAB Solving 5 Unknowns with Gauss-Seidel in MATLAB

    Homework Statement 100 - 100C1 = 0 100(C1) + 5(C3) - 150(C2) - 30(C2) = 0 150(C2) + 5(C4) - 75(C3) - 37,5(C3) = 0 70(C3) + 10(C5) - 40(C4) - 20(C4) = 0 75(C4) - 80(C5) - 24(C5) = 05 unknowns and 5 equations my question is " how can i solve his problem using Gauss-Seidel method in MATLAB...
  30. N

    Remainder Theorem with 2 unknowns.

    Homework Statement When rx^3 + gx^2 +4x + 1 is divided by x-1, the remainder is 12. When it is divided by x+3, the remainder is -20. Find the values of r and g. Homework Equations The Attempt at a Solution r=f(1) =r(1)^3 + g(1)^2 + 4(1) +5 =r + g +9 r=12 r+g+9=12 r+g= 3...
  31. A

    How Do You Solve a Polynomial with Two Unknowns and Given Roots?

    [SOLVED] polynomial with two unknowns Homework Statement The graph of f(x)= 3x^4 + 14x^3 + px^2 + qx + 24 has x-intercepts -4 and 2. Determine the function. The Attempt at a Solution I could solve it if there were only one unknown but i don't know how to do it if there are two...
  32. R

    Finding two unknowns from varience and mean

    the data given below are from a discrete distribution with positive integer values.there are two values which are unknown, namely "a" and "b". 8,5,3,6,5,9,a,b if the mean and varience respectively are 6.5 and 7.75, what are the possible values of "a" and "b"? so far i have that...
  33. A

    Finding the unknowns of irrational equation

    Homework Statement For the following irrational equation x^2 + 7x + 10 + \sqrt{x^2 + 7x + 12} = 0 Find all possible unknown of X. Homework Equations None. Just your ability to solve equations. The Attempt at a Solution First of all, I am not allowed to use a calculator to...
  34. X

    Solving Unknowns for 10 N Force and 3.0 kg Box

    I'm having trouble finding the unknowns for this problem. There is a picture of a box and m=3.0 kg F1 is pushing to the right and 10 N is pushing to the left. I have to find Fnet and a. btw, It is free body diagram.
  35. N

    Free fall body problem, stuck with 2 unknowns

    (moved to Intro Phys... - Doc Al) ---------------------------------------------------------------------- Hi guys, this is my first post in this forum. I feel lucky to come across a place like this and even more thankful if i can get help on this problem that I've been spending a loooot of...
  36. R

    Inequality involving two unknowns and factorials

    I need to prove the following: n!/r! >= r^(n-r) With r and n as natural numbers and n>=r I know the LHS will end up being (n-r) terms long as the first r! will cancel out of n! (n>=r), but as they're both unknown, I just left it as 1*2*3*...*(n-2)*(n-1)*n 1*2*3*...*(r-2)*(r-1)*r and I looked...
  37. Q

    Engineering Circuit design, 2 equations, 3 unknowns

    I'm working with this circuit to design an ambient light meter. http://img201.imageshack.us/img201/6479/cktyu0.jpg We were given steps to go about solving for different values of the components in the circuit. First we're to solve for the gain and thus V1 which I found to be...
  38. B

    How do I solve for two unknowns using two equations?

    Homework Statement I can't remember how to solve these equations like this one. I need to solve for each variable. I'm not sure I've ever known how to do this. -720 + Tab*cos(36.8699) + Taf*cos(20.556) 660 + Tab*sin(53.1301) + Taf*sin(69.444) I need to solve for both Tab and...
  39. N

    When Does the Angular Velocity of a DC Motor Reach Zero?

    Homework Statement At t=0 the current to a dc electric motor is reversed, resulting in an angular displacement of the motor shaft given by theta (t) = ( A)t-( B)t^{2}-( C)t^{3} At what time is the angular velocity of the motor shaft zero? Homework Equations quadratic The Attempt...
  40. B

    Solving 3 Equations & 3 Unknowns with Voyage 200 (Ti-89)

    Hey guys, I was wondering...Can I make my voyage 200(basically a Ti-89)...solve for 3 equations and 3 unknowns? If so, how? Also, I was wondering, can I make it solve 3x3 matricies, which include numbers on the lower 2 rows...but the top row(across)...has i,j,k on it. Anyway to use the...
  41. L

    Identifying Unknown Solutions in Chem Lab: NH3 + CuSO4 and NaI + CuSO4 Reactions

    Chem Lab "ID of Unknowns" I had to find 5 unknown solutions in a recent chem lab and now I am doing the equations, but I am not sure about two of them: Deep blue percipitate NH3 (aq) + CuSO4 (aq) -------> Cu(NH3)4 SO4 (s) brown heavy percipitate 4NaI (aq) + 2CuSO4 (aq) -------> 2CuI (s)...
  42. D

    No HUP, a universe without unknowns?

    If the universe did not act in accordance with the HUP would it display different properties to the universe we know and love? A large number of people have difficulty accepting the underlying concept of the universe being undefined but what would be the alternative? Would the universe be...
  43. K

    Identifying Unknowns in a circuit

    When using an analog voltmeter how do you identify the difference between resistors, capacitors, and inductors?
  44. J

    Calculating Steam Turbine Work & Power from 2 Unknowns

    A steam turbine has an inlet of 2kg/s water at 1000kPa and 350C and velocity of 15m/s. The exit is at 100kPa, 100% quality and very low velocity. Find specific work and power produced. I have done a lot of these problems but it usually says adiabatic or the inlet and exit temp is the same...
  45. K

    Single equation with 2 unknowns

    hiya, if i have the equation: y=0.2sin(5x-1100t) and i need what t = when y - 0.1 how do i do this without knowing x / how do i find x? thanks u - kait
  46. B

    3 equations, 3 unknowns, how do i solve ?

    3 equations, 3 unknowns, how do i solve!? hi everyone, i have 3 equations and 3 unknowns: x = (a/b) + c y = (a/(b+1)) + c z = (a/(b+7)) + c where x, y, z are given in the problem (real #'s), and we need to find the values of a, b, and c. can anyone tell me how to go about this...
  47. I

    How to test if some unknowns are covalent or ionic?

    So...how do you carry out an experiment to test if some unknowns are covalent (polar or non-polar) or ionic? Unknowns: C6H12O6 --NaCl --CH4N20 --C6H8O7 :confused:
  48. wolram

    Finding a Solution with Unknowns

    How do you go about finding a solution if there are several unknowns ? i seem to be useing instinct rather than logic, or a bit of both, to get things fixed quickly, i know it is the wrong thing to do ,one should start solving a problem from the beginning or end, but this way seems to take much...
  49. D

    What is the relationship between simple harmonic motion and amplitude?

    Hi, I'm having trouble with this problem because I don't know how to deal with all these unknowns: 4. A block attached to a spring with unknown spring constant oscillates with a period of 2.0 s. What is the period if : a. The mass is doubled? b. The mass is halved...
  50. S

    Uncovering Unknowns in the Evolution Timeline

    Where are the current unknowns in the evolution timeline? It is my knowledge that the progressions from gaslike "soup" to amino acids is believed to have been caused by intense lightning and UV radiation. But the mystery is how we went from amino acid to protein? Are there any other unknowns...
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