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  1. Q

    Showing a vector field is imcompressible

    Homework Statement Homework Equations The Attempt at a Solution As you can see, the solution is shown just below the question. Essentially, I don't understand how the x, y and z component of the vector field has been separated because the numerator of the vector field's fraction is: (x^2...
  2. Q

    How to work out expected frequency from normal distribution

    How is the expected frequency column worked out for each interval of trains? 2) My attempt Take the first interval, 60 - 62, I thought about doing this: (62 - mean) / standard deviation (62 - 67.45) / 2.92 = - 1.866 using Z score < - 1.886, from the normal distribution table, I get: 1 -...
  3. Q

    Determining the forces in a framework

    The framework is attached below. I've tried going to each joint and resolving the forces vertically and horizontally. I've got to joint B and I'm stuck, because I have three unknown members there. And its the same if I go to joint J. what do I do?
  4. Q

    Ground water flow question

    Its attached below. I don't understand how you work out the total head. Can someone explain how you do it? I'm really struggling. I know how to do the elevation, which is just the height above/below the datum level. And I've checked the solutions as well, it seems like you're supposed to work...
  5. Q

    Determining forces in members of a structure

    Homework Statement I want to find the force in the vertical purple member. Assuming I know the forces in all the other members, theres a problem with working out the force in the purple member. (Bear in mind, I'm using the method where I assume equilibrium at each joint in the...
  6. Q

    Directional derivative question

    I've done the first part, but I'm stuck on the second paragraph of the question. Maybe I'm being stupid, I don't even understand exactly what is meant by, 'the level curve'. I also don't quite understand the whole concept of directional derivative. When it says, 'the gradient in the...
  7. Q

    Use of guassian elimination to find the determinate of a matrix

    Homework Statement I have to find that the characteristic polynomial for a 3x3 matrix A, which is effectively the same as finding the det(A - I*lamda) matrix A is: the problem is that when I've written out 'A - I*lamda' in matrix form, the three values at the bottom left of the matrix...
  8. Q

    What evidence supports the big bang theory?

    off the top of my head: - isotropic microwave radiation corresponding to 3.73K blackbody curve - hubble's law - red shift of galaxies - 3:1 ratio between hydrogen and helium, and the relative abundance of them is there any more? and also, can someone explain the hydrogen-helium ratio thing...
  9. Q

    Confusion about the accelerating expansion of the universe and Hubble

    My school textbook says that discovery of the 1a supernova was what led to the understanding that the universe expansion is accelerating but doesn't hubble's equation already suggest that the universe would expand at an accelerating rate? V = Hd (V = velocity, H = hubble's constant, d =...
  10. Q

    Why do geosynchronous satellites have to orbit above the Equator?

    I get that they have to be at the same position relative to the earth but why is it that they have to be specifically above the equator? thats the sense I get from the textbooks, they all seem to emphasize the satellite being above the Equator can't you have a geosynchronous satellite...
  11. Q

    Show how gravitational potential varies between the earth and the moon

    Homework Statement gravitational potential at surface of the earth = -63MJkg-1 gravitational potential at surface of the moon = -2MJkg-1 The attempt at a solution I thought gravitational potential was a scalar, so in which case, you would surely just add up the potential due from both...
  12. Q

    Single slit width change, how would fringes differ?

    just to be clear, this is single slit diffraction of light if the slit width is made narrower, this would lead to more diffraction, so the fringe width would be wider, yeah? but I'm a bit confused, because is this basically the same as saying the fringe separation would be wider?
  13. Q

    Young's fringes experiment, interference fringes

    Homework Statement (this is high school level) The pic below shows interference fringes observe in Young's fringes experiment: Explain why wider slits at the same spacing could produce fringes at the outer edges brighter than some of the fringes nearer the centre. Bear in mind there was a...
  14. Q

    Diffraction and intensity of fringes

    I'm not sure if I've understood my textbook correctly. Can you tell me if my current understanding is correct: - in a single slit diffraction theres a wide central fringe which is twice as wide as all the other outer fringes - if we had a double slit diffraction instead of a single slit...
  15. Q

    Waves and phase difference

    Homework Statement Its part B ii) and iii) that I'm stuck on. Homework Equations Apparently for stationary waves, the phase difference between two particles = m(pi), where m is the number of nodes between the particles. This is according to my textbook here: The Attempt at a Solution...
  16. Q

    About wave polarisation

    I have two queries: - if unpolarised light passes through a polaroid filter so that light coming out of the filter becomes polarised, would intensity (brightness) of the light become reduced as a result? - if you have a polarized wave, and it passes through a filter that has a gap which is...
  17. Q

    Can someone check my answers to these four wave questions

    My textbook didn't include answers to these questions at the back. Question 1: my answer: Question 2: my answer: part A and B of the question are shown by wavefronts A and B in the picture below, Question 3: my answer: and just out of...
  18. Q

    Concept of 'work done' on a smooth slope (high school-level physics)

    Say you have an object on a smooth friction-less slope, and a force 10N (acting parallel to the slope) is applied to it to move it at a distance 5m up the slope. Work done by the force is: force*distance. In this case, 10*5 = 50 joules of energy Does all that energy get transferred to...
  19. Q

    Is there a difference between contact time and impact time? (collsion)

    This is from my textbook: I'm slightly confused about the bit underlined in red. Do you think its in reference to the sentence just before where it talks about situations of vehicles remaining tangled? (so for other cases, contact time = impact time, right?) also, I don't really...
  20. Q

    Need help on a forces and equilibrium question

    Its part B that I'm not sure about. I know how to do it. But I'm confused about why the support force is not acting vertically upwards (so no horizontal component). I assumed that the support force would always be directly perpendicular to the ground/slope/wall. Can someone explain this?
  21. Q

    All baryons eventually decay into protons, is this the same with anti-bayrons?

    (high school level physics btw) apparently all baryons eventually decay into protons, so I was just curious to know if this was also true of anti-baryons?
  22. Q

    Why does it matter whether or not an ammeter has zero resistance?

    Apparently an ideal ammeter has zero resistance. But for a series circuit, why does it matter? The purpose of an ammeter is to give the reading for the amount of current going round a 'loop' of circuit. Having some resistance does not prevent the ammeter from giving a true reading, right? So...
  23. Q

    What is the feynman diagram for electromagnetic force between an electron and proton?

    Would it just be the same as with two electrons? (or any other pair of particles with the same charge) I'm kinda in two minds, I suspect that is wrong because wouldn't the fact that they attract each other (instead of repelling) means that the diagram would be drawn differently?
  24. Q

    Can someone explain how pair production happens?

    I know that if a photon has enough energy, it can split off into a particle and anti-particle. But how does that happen exactly? Does the photon just randomly decides to split off? With annihilation (opposite of pair production), the process is much easier to visualize for me, because you...
  25. Q

    Electric circuit explanation question involving voltage changes

    Homework Statement The filament of the lamp in X breaks and the lamp no longer conducts. It is observed that the voltmeter reading decreased and the lamp Y glows more brightly. a) Explain without calculation why the voltmeter reading decreases. b) Explain without calculation why the lamp Y...
  26. Q

    Do ALL hadrons eventually decay into protons?

    I have two sources, one (school textbook) is telling me that ''all hadrons eventually decay into a proton'', whereas a few other people have told me that ''only bayrons decay into protons''. I want to know because I originally wanted to find out whether mesons decay into protons, and mesons...