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  1. J

    Coefficent of friction for a box moving at cosntant speed

    Homework Statement A horizontal force fo 190N is needed to pull a 70kg box across a horizontal floor at a constant speed. What is the coefficent of friction between the box and the floor? Homework Equations Fnet = ma The Attempt at a Solution My setup is F - F_f = m*a But I...
  2. J

    Find the final temperature of water

    Homework Statement What is the final temperature of water if 175 g steam at 150 C loses 423 KJ of energy? Homework Equations Q = M *C_p * Δ T Q = m * heat of (phase_change) The Attempt at a Solution This is how I would go about solving this problem. Going from steam to water requires...
  3. J

    Prove absorption law

    Homework Statement Prove the absorption law A U (A and B) = A Homework Equations The Attempt at a Solution I need to prove the sets are equal. I don't know how to prove the right hand as a subset of the left hand. For left hand as subset of right hand, it's pretty simple (we can define...
  4. J

    Sample mean and linear relation?

    Homework Statement The book states the following: The sample mean is defined by: \bar{x}=\sum_{i=1}^{n}x_{i}/n The computation of the sample mean can often be simplified by noting that if for constants a and b, y_{i}=ax_{i}+b, then the sample mean of the data set y1 , . . . , yn is...
  5. J

    Computational mathematics for a messed up student

    I am a Computer Engineering major. I begin to like analyzing things (I always do). I love testing things, and I really have the patience to do analyzing things, google for answers, reading and researching for answers. But I am not a very strong math student (pretty careless and my fundamental...
  6. J

    Like poles attract

    Not meant to be a homework question, but since I don't have any valid data on hands so I am hesitate posting this in classical physics forum. The headline suggests the opposite of what we physics tell us. But my question is, is it theoretically possible to make like poles attract (assuming no...
  7. J

    Method of undertermined coefficients (IVP)

    Homework Statement Find the solution of the given initial value problem. \[y''-2y'-3y=3te^{2t}\] Homework Equations The Attempt at a Solution (1) the homogenous solution is given by \[y_{h}=c_{1}e^{3t}+c_{2}e^{-t}\] (2) the particular solution is in the form \[y_{p}=(At+B)e^{2t}\] (3)...
  8. J

    De Moivre’s Theorem

    Homework Statement Let z = 1 − i. Find z^10. Homework Equations The Attempt at a Solution |z|= \sqrt{(1)^{2}+{-1}^2} a=|z|cos(\theta ), b=|z|sin(\theta ) and we find that \theta = -pi/4 or 7*pi/4 (Accoridng to this, it is in the fourth quadrant )...
  9. J

    Find graphically the value of x satisifies this equation

    Homework Statement Find graphically the value of x in the interval [0,2] which satisfies the equation \frac{\mathrm{d} }{\mathrm{d} x} \left ( \frac{e^{-x^2}sin(x^{2})}{cos(x)+3} \right )=\frac{x^{2}}{10+x} Homework Equations Definition of limits f ' (x0) = lim x -> x0 f(x)-f(x0)/(x-x0)...
  10. J

    Interfence of thin film

    Homework Statement White light is sent downward onto a horizontal thin film that is sandwiched between two materials. The indexes of refraction are 1.80 for the top material, 1.66 for the thin film, and 1.50 for the bottom material. The film thickness is 5.4 10-7 m. Homework...
  11. J

    Find the particular solution of this difference equation (solve most of it)

    Homework Statement Find the particular solution. y(k+2) + y(k+1) -6y(k) = 3^(k) Homework Equations The Attempt at a Solution Still need to be answered Question (1): Before finding the particular solution, is it true that we should ALWAYS get the homogeneous solution...
  12. J

    Deduce the solution from weight function

    Homework Statement Convolution-Summation of a First Order System with Constant Coefficients http://dl.dropbox.com/u/14655573/1.PNG [Broken] Homework Equations The Attempt at a Solution The solution from the lecture [PLAIN]http://dl.dropbox.com/u/14655573/2.PNG [Broken]...
  13. J

    Problem with substitution in a difference equation

    Homework Statement Verify that the response of the system governed by the 1st order different equation y(k)=bu(k)+ay(k-1) is given by this solution y(k)=\frac{b}{1+a}\left [ (-1)^{k}+a^{k+1} \right ] for u(k) = (-1)^k The Attempt at a Solution The solution said we can verify this...
  14. J

    Determine whether this is an exact equation [differential]

    Homework Statement Determine whether this is an exact equation. If it is, find the solution. \[\frac{\mathrm{d}y }{\mathrm{d} x} = -\frac{ax+by}{bx+cy}\] Homework Equations The Attempt at a Solution If I moved the right side to the left (because an exact equation has the form...
  15. J

    Determine the interval validity of this separable equation

    Homework Statement Find the solution of the given initial value problem in explicit form and determine the interval in which the solution is defined. \[x dx+ye^{-x}dy = 0\] with initial condition y(0) = 1 Homework Equations The Attempt at a Solution I solved the first part...
  16. J

    Find focal length for meniscus convex

    Homework Statement Find focal length for meniscus convex (3) Given r = 15, and n = 1.5 Homework Equations Lens maker's equation The Attempt at a Solution I can find the rest except #3 and #6 (they are opposite sign of each other) I had (1/r1 - 1/r2) gives zero... which is wrong..... I...
  17. J

    Solve this simple differential equation

    Homework Statement \[\frac{\mathrm{dy} }{\mathrm{d} x} = \frac{x - e^{-x}}{y + e^{y}} \] Homework Equations The Attempt at a Solution This is how I did it.... [1] multiple \[y + e^{y} (dy) = x - e^{-x} (dx)\] [2] integrate both sides and I get \[\frac{1}{2}y^{2} + e^{y} =...
  18. J

    Sound wave interfernce on a large circle

    Homework Statement Given two isotropic point sources of sound \[s_{1}\] and \[s_{2}\]. The sources emit waves in phase at wavelength 0.50m; they are separated by D = 1.75m. If we move a sound detector along a large circle centered at the midpoint between the sources, at how many points do...
  19. J

    Help determining the sound wave function

    Homework Statement [PLAIN]http://dl.dropbox.com/u/14655573/110218_203248.jpg [Broken] Part (1) The figure shows the output from a pressure monitor mounted at a point along the path taken by a sound wave of a single frequency traveling at 343 m/s through air with a single frequency...
  20. J

    Find the top vertex coordinate of a regular tetrahedron

    Homework Statement A regular tetrahedron has the vertices of its base A(1,1,0) B(3,1,0) C(2,1+(3^(1/2),0). Find coordinate of vertex S? Homework Equations The Attempt at a Solution If this is a tetrahedron Then we know the length by caclulating the distance formula, which gives...
  21. J

    Find wavelength for a standing wave

    Homework Statement Two sinusoidal waves with identical wavelengths and amplitudes travel in opposite directions along a string with a speed of 10 cm/s. If the time interval between instants when the string is flat is 0.50 s, what is the wavelength of the waves? Homework Equations v = w/k =...
  22. J

    Transverse velocity of a standing wave problem

    Homework Statement In the figure it shows a pattern of resonant oscillation of a string of mass m = 2.5g, length L = 0.800m and under tension T = 325.0N. What is the wavelength of the transverse waves producing the standing-wave pattern, and what is the harmonic number n? What is the frequency...
  23. J

    Parametrize surfaces

    Homework Statement The part of the hyperboloid x^2 + y^2 - z^2 = 1 that lies to the right of the xz-plane The Attempt at a Solution Clearly, since it's demanded in turns of xz-plane, we have y = sqrt( z^2 - x^2 - 1) To parametrize it, we can simply use x = x, z = z, and y =...
  24. J

    Trig identity in superposition

    Homework Statement For two waves in superposition, we have, let say \[y_{1} = Asin(kx-wt), y_{2} = Asin(kx-wt+\Phi )\] We use the trig identity sin A + sin B to simplify the combination Whereas for standing waves, we use the trig identity sin(a +/- b) to combine the result. As I...
  25. J

    Standing waves

    Homework Statement This is what my professor wrote on the board. Suppose the condition is as follows y(0) = y(L) = 0 link to img http://www.izhuk.com/painter/image2.php?id=1286387629-69-86-215-102&md5=c054d375567134a9faa133b47fe690b2 This is the fundamental harmonic - with nodes appear at x...
  26. J

    Prove F = grad(f)

    Homework Statement For two variables, F = grad(f) if only if partial P / partial y is equal to partial Q / partial x where, P and Q represent the x, y function, P(x,y) and Q(x,y) For example: F(x,y) = P(x,y) + Q(x,y) Now the question is, for three variables, I have P + Q + R. Is...
  27. J

    Parametric equation of tangent line

    Homework Statement Find parametric equations for the tangent line to the curve with the given parametric equations at a given point. \[x = t^5, y = t^4, z = t^3\] at point (1,1,1) Homework Equations The Attempt at a Solution So we need to have direction vector, and a point. To find...
  28. J

    Engineering Determine currents of a circuit

    Homework Statement For the circuit in the figure, determine i1to i5 http://i55.tinypic.com/dokoc5.png Homework Equations current division: in = (Requivalence / Rn) * itotal Requivalence in parallel = R1*R2 / R1+R2 The Attempt at a Solution || (parallel), and +s (series) 1ohms ||...
  29. J

    Ideas of field

    Homework Statement Here is an interesting reading to my question. http://coraifeartaigh.wordpress.com/2010/02/27/what-is-a-field/ The author wrote: The reason he said each charge will experience a different force is assuming different r (and not a constant r)? Another question is to...
  30. J

    Dv/dt in a sound wave problem

    Homework Statement The speed of sound in air (in meters per second) depends on temperature according to the approximate expression v = 331.5 + 0.607T where T is the Celsius temperature. In dry air, the temperature decreases about 1C for every 150m rise in altitude. a. Assume this...
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