# All Questions

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### If the universe has no center, how it can collapse?

After reading Does the universe have a center? and trying to find a place in my mind for "There exists no center", I asked my self: If there is no center, in what direction our universe will ...
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### Is a trebuchet a physics problem with spherical symmetry?

I am investigating the physics behind a sling trebuchet in order to derive the equations of motion for the payload m (as seen in the figure.) To begin I have to define what generalized curvilinear ...
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### Solutions for Kittel's Introduction to solid state physics 6th edition?

I'm looking for the solutions of Kittel's 'Introduction to solid state physics' 6th edition. I can only seem to find the solutions for the 8th edition online. Does anyone have the pdf to it? Or ...
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### Why capacitor charging is taken from negative infinity?

Why in Engineering disciplines ,when finding voltage across capacitor the time as limit of integral is taken from negative infinity to t and not zero? The same can be seen for signals,Laplace though ...
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### Two point charges of the same absolute value Q = 50x10 ^ -6 , but of opposite sign

Two point charges of the same absolute value Q = 50x10 ^ -6 , but of opposite sign , generate fields at P , the vacuum as shown in Fig . Characterize the resulting electric field in P. OBS: I ...
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### Two resistances are joined in parallel and their equivalent resistance is 3/5 ohm

Two resistances are joined in parallel and their equivalent resistance is 3/5 ohm One of the resistances is disconnected and the effective resistance becomes 3 ohm What is the resistance of the wire ...
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### dot product of two vectors in spherical polar coordinates, do I have to convert to cartesian coordinates?

For two vectors $p1=(r1,\theta_1, \phi_1)$ and $p2=(r2, \theta_2, \phi_2)$ I want the dot product p1.p2. However, the solutions I have seen, involve finding the components in Cartesian coordinates and ...
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### Conditions for supersonic flat plate problem

I am interested to solve "supersonic flat plate problem". I want to ask that how do conditions for this problem set?