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  1. Moara

    Static structure - find a fourth relation

    but I think that horizontal and vertical equilibrium plus rotation equilibrium of AC and BC around C is correct
  2. Moara

    Static structure - find a fourth relation

    I probably did a mistake in my calculations
  3. Moara

    Static structure - find a fourth relation

    It appears that I have to look AC and BC separately right
  4. Moara

    Static structure - find a fourth relation

    It appears that I have to look AC and BC separately right
  5. Moara

    Static structure - find a fourth relation

    with that in mind, I did the equilibrium of rotation looking to C, from bar AC, getting another equation and finding ##H_A = \frac{90}{7}##, is it correct doing that ?
  6. Moara

    Static structure - find a fourth relation

    I don't think I understand how am I supposed to remove one support, could you clarify, please? Meanwhile, I tried to split the structure looking only at the branch AC, can I say that in C there will be only horizontal forces, hence finding that ##V_A = 10 \ kN## ?
  7. Moara

    Static structure - find a fourth relation

    First, since A and B are articulated, the moments due to A and B are zero. Now, we may call reaction forces in A, ##V_A## and ##H_A## and in the same way, call the reactions in B as ##V_B## and ##H_B##. With that and Newton's third law, I managed to find three equations (equilibrium of...
  8. Moara

    Conditional probability and criminal DNA analysis

    We know that ##P(A-) = (95\% \cdot 0.5\% + 5\% \cdot 98.5\% )## and ##P(guilty \ and \ A-) = (95\% \cdot 0.5\%)##, so letter a) is just ##P(guilty \ and \ A-)/P(A-)##. What I tried to do in letter b) was again using the conditional probability theorem. First calculating the probability that...
  9. Moara

    Observation of events and analysis of the associated Hypotheses

    So you agree with my part c) calculation ? What about letter b), as told before, I don't think I truly understand what that relative frequency question mean.
  10. Moara

    Observation of events and analysis of the associated Hypotheses

    so you agree with my calculations in c), but don't agree with the scientist's assumption that the events are independent? And letter b) could you clarify what that relative frequency interpretation mean ?
  11. Moara

    Observation of events and analysis of the associated Hypotheses

    For letter a), i think that he is assuming that each hypothesis is independent, and that they are mutually exclusive. For letter b), I understand that it indeed admits the relative frequency interpretation, since the the experiment is being produced several times. For letter c) we do the...
  12. Moara

    LaTeX Program or platform for figures and diagrams

    If anyone can recommend platforms or programs for doing these type of figures and diagrams, even if it doesn't have anything related to latex, I would be gratefull to
  13. Moara

    LaTeX Program or platform for figures and diagrams

    When using latex for writing problems in physics, I find it difficult to make diagrams or figures (such as circuits, atwood machines, lenses, ...) so I wonder if anyone has some recommendations of programs or platforms that can make this "drawings" easy, possibly without the necessity of coding...
  14. Moara

    Wire rotating inside a magnetic field

    Oh, now I see, I was messing up things. Using the superposition principle to "complete" a triangle with the center, middle point and edge point, you form a triangle Wich has constant area in a constant magnetic field, so the total induced potencial difference along it's perimeter is zero. This...
  15. Moara

    Wire rotating inside a magnetic field

    I managed to solve the problem, using Faraday's law it turns out that the flux through the imaginary triangle is constant. Now, I have a question, in this case, of a triangular loop of wire, since the area of the triangle and the magnetic field is constant, the flux is constant, therefore the...
  16. Moara

    Wire rotating inside a magnetic field

    For a infinitesimal wire of lengh dx, the induced potential difference in an uniform B field perpendicular to it's motion is : dE=B.Vp.dx, where Vp is the component of the velocity perpendicular to the wire. Looking to the big wire I tried to take an arbitrary point express dE in function of...
  17. Moara

    Electron moving inside a region of homogeneous electric field

    Yes, found out that conservation of momentum in x is still valid, thank you
  18. Moara

    Electron moving inside a region of homogeneous electric field

    a) since the eletric field is perpendicular to the inicial velocity, the x component is constant, hence Vf.cos45=Vo. This gives Vf=0,6√2.C b) Ei=γi.Eo , γi=5/4 , Ef=γf.Eo , γf=5/(2√7) Finally, Ei+e.E.d=Ef. Apparently this is incorrect, why??
  19. Moara

    Spherical gas distributed symmetricaly over space

    You say that equation 3 is valid, but it is not valid to integrate it over the whole volume ? This change of the scenario would be caused by what? Is it because of the gradient pressure, like if you were assuming all gas to be at the same thermodynamic equilibrium?
  20. Moara

    Spherical gas distributed symmetricaly over space

    . We have that energy in a infinitesimal Spherical layer with number of mols dn is: dU=Cv.T.dn (1) But by the ideal gas law: PV=nRT (2) Differentiation gives: PdV+VdP=RTdn (3) (3) in (1) and using CV=3R/2 (monoatomic) gives: dU=3/2.(PdV+VdP) (4) Integration of (4) over the whole gas will...
  21. Moara

    Flux of Electric Field through a cone

    Here is the solution I saw. The sentence : " temos que" is equal to " we have that"
  22. Moara

    Flux of Electric Field through a cone

    Since there is no charge inside the cone, the total flux through its surface is zero, hence Ø(lateral surface)+∅(base surface)=0. But ∅(base surface)=E.πR².cosΩ, because electric Field is homogenous. But by the figure, Ω is just arctg(h/R). So Ø(lateral surface)=-E.π.R².R/√(R²+h²). This is not...
  23. Moara

    Block in a rotating cylinder

    Actually no, since at all times the three vectors W,C and R (where R is resultant of N and friction) are in a plane I am trying to fix this plane (although it changes in time ) and figure out what type o figure W+C makes. It appears to me is going to be similar to letter a, but instead of a...
  24. Moara

    Block in a rotating cylinder

    Sorry about bumping the problem, but apparently there is a different approach to part a and b using geometry. In part a it is clear that we have A fixed plane containing the vector g and vector w^2.R. In the reference frame rotating with the block we can see that the resulting field of these two...
  25. Moara

    Probability of hitting a rotating disc

    Found my mathematical error while writing my attempt, thank you
  26. Moara

    Probability of hitting a rotating disc

    Well, The movement is in the horizontal plane, sorry about the image.
  27. Moara

    Probability of hitting a rotating disc

    There are two points of the smaller disck such that a line is tangent to the two discks and passes by that point. If the particle leaves of any point belongin to the arch that connects these two points, then it will hit the other disck. So I managed to calculate the value of this arch and divide...
  28. Moara

    Eletromagnetism: Copper Plate on a Spring Oscillating in a Magnetic Field

    In my book the answer is c. I think that, although physically incomplete or purely theoretical, the problem wants to handle only with some "easier" observations of the energy associated with B and E and the induced charges. By the way, I don't know where it is from, but does not come from...
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