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  1. C

    Multiple temperature reservoirs

    I have a problem: A typical compartment domestic refrigerator with freezer can be represented by 3 temperature reservoirs connected to the cyclic device which absorbs W' of work. - cool box at Tc = +279K from which Q'c heat is extracted - freezer at Tf = -269k from which a further Q'f...
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    Principal stresses help ?

    Ah yes i think I have a solution to this problem now using the general formula for plane stresses. There is a second part to the question where it now asks to find the angle which the maximum stresses make with the direction sigma(x)? Does this involve the 2D Mohr Circle?
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    Principal stresses help ?

    Principal stresses help plz? I am looking through past paper examinations and have come a across a question: At a certain critical point in a stressed component, calculations show that the stresses are sigma(x) = 220MPa sigma(y) = -95MPa and shear = 60MPa Find the maximum and minimum...
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    Current against slip relationship of induction machine?

    Current against slip relationship of induction machine?? Please could someone explain to me the relationship between the current and the slip value of an induction machine. I have plotted a graph and Im wondering how to interpret this? Thankyou.
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    Understanding of the fourier coefficients?

    Im just looking through examples of finding the fourier coefficients. in one particular example bn is found to be = (-1/npi) (cosnpi - cos 0) then it says this is 0 when n is even and 2/npi when n is odd are we just substituting values of n e.g. 1,2,3..... to find this result? i...
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    Is the function odd, even or neither?

    The function f(x) 1, -pi < x < 0 0, 0 < x < pi now after sketching the function i believe i am correct in saying it is neither symmetrical about the x axis or the origin and therefore is neither odd nor even? It is a square wave? Am...
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    To find the sum of a fourier series ?

    to find the sum of a fourier series....? My problem is: I must find the sum of ((-1)^(n+1))/2n-1 between infinity and n=1. I have looked in all my available textbooks for a clear example but im still unsure as to how i should approach the problem? Help with this would be much...
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    Please check my solution

    I have to differentiate (e^-x) ((1-x)^1/2) twice: The first time i differentiate i get (-e^-x) ((1-x)^1/2) + (e^-x) ((1-x)^-1/2) (-1/2) then differentiating this i get [(e^-x) ((1-x)^1/2)] - [(e^-x) ((1-x)^-1/2) (-1/2)] + [(-1/2e^-x) (1/2(1-x)^3/2) + ((1-x)^-1/2) (1/2e^-x)] are...
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    Please check this differentiation result

    I have to differentiate (e^-x) ((1-x)^1/2) my answer is: (-e^-x) ((1-x)^1/2) + (e^-x)/((-1/2 + 1/2x)^-1/2)) is this correct? thankyou
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    Table leg design

    table leg design...... Suppose i want to make 4 table legs from aluminium square should I go about designing the dimensions of the square tube? The table itself needs to support a load of 90kg through the four legs. Help on this would be very much appreciated. Cabellos
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    Aluminium framework .

    aluminium framework..... I am designing an aluminium frame bed. I have desided to use aluminium extrusion either square or rectangular shape to form the main 4 bars at the base supported by 4 legs. I will use panels of plywood at the centre holding the mattress. My question is.......suppose...
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    Would this work ?

    Ok thanks. Could you offer me some advise on how i might go about analysing the bending stress of the material for a certain size?
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    Would this work ?

    Would this work....? Im designing a folding bunk bed and was wondering whether to keep the weight down I could use a metal wire mesh material as the top bunk fixed to aluminium square tube? Also would it be possible to attach this to the tube main frame fairly easily and how much does the...
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    Stress analysis of bed design

    Stress analysis of bed design.... I have a bed design and i need to do a stress analysis of the top bunk under a 90kg load. I will be designing it from 20mm thick plywood but i need to work out whether this is thick enough to support the load and also determine the width of the leg supports...
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    Designing folding legs for a bunk bed .

    Designing folding legs for a bunk bed..... Im having trouble finding a suitable hinge mechanism which would allow 2 legs under a bed to be locked and pulling them down into a vertical position they would lock. Does anyone have any ideas or links to a suitable hinge design. Thanks
  16. C

    Directional derivative?

    how about -3?
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    Directional derivative?

    ok sorry. i think iv got the answer now. -1 ????
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    Directional derivative?

    the gradient i found was -2z/(2x+y)^2 i + -z/(2x+y)^2 j + 2x+y/(2x+y)^2 k i thought the directional derivative was then s.grad what should the answer be?
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    Directional derivative?

    Im doing the following question: calculate the directional derivative of the function f(x,y,z) = z/(2x + y) at the point (0,1,1) in the direction d = 2i - 2j - k could someone please check my answer is correct as i calculated -3i -6k Also how do i find the unit vector in the direction...
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    Differentiating with respect to

    differentiating with respect to.... I have a question on differentiating the function z/(2x + y) with respect to x. Is the answer -2z/(2x + y)^2 ? Thanks:smile:
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    Partial differentiation

    i need some sleep!! Yeah i meant y^3 lol !
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    Partial differentiation

    ooops im getting myself all confused now. I know how to do partial differentiation after all. I was reading the wrong solution as the question was z = x^2 y^2 and ofcourse dz/dy would = 3x^2 y^2 !!
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    Partial differentiation

    Iv forgotten the basics of this. How do we go about differentiating 3x^2 y^2 w.r.t y? I know the answer is 3x^2 y^2 but could someone explain this for me please?
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    Inverse laplace method for equation .

    inverse laplace method for equation ..... Just doing some revision but im a little stuck on how to find the inverse laplace of 1/s(s-2)
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    Laplace transform sint * cost

    i meant multiplication
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    Laplace transform sint * cost

    yes i did know that but i didnt think it was as simple as that. From reading the certain rules we can apply to problems e.g the shift rule to solve L(sin2t * e^3t) do we HAVE to use the shift rule or can we seperate each part and solve then multiply them together?
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    Laplace transform sint * cost

    how do i go about solving the laplace transform of sint * cost ??? i know the answer becomes 1/(s^2 + 4) but what is the method? thanks.
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    Differentiating with respect to time

    How do you go about differentiating rcos$ with respect to time....? In the book im studying from it says d$/dt d/d$ (rcos$) is the process to find the answer... but what does this mean...?
  29. C

    Integrate with respect to x it -cos(xy) / y
  30. C

    Integrate with respect to x

    I just need a check on when integrating sin(xy) with respect to x? Does this become -cos(xy) or -cos(x) thanks