# Tagged Questions

Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework questions.

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### Deriving the Laguerre–Gaussian equation [on hold]

How does one derive the Laguerre–Gaussian equation? $$x\frac{d^2y}{dx^2}+\left(1-x\right)\frac{dy}{dx}+ny=0$$
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### The dimensional formula of distance travelled in $n$th second

I read that the dimensional formula of distance traveled in $n^{th}$ second is same as that of velocity. Okay, the formula for the distance traveled in $n^{th}$ second is $s_t= u+\frac{a}{2}(2t-1)$ ...
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### Electric Field for a hollow sphere with point charge

I think I am over thinking this question: A point charge of $-2\space\mu C$ is located in the center of a hollow sphere. The internal and external radius of the sphere is given by $6.5$ and ...
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### How to find the final momenta of these objects?

Suppose two objects collide head on, where initially object 1 (mass $m_1$) is moving and object 2 (mass $m_2$) is stationary. Now assume that they have the same mass, so $m_1 = m_2$. Which ...
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### Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
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### A sphere rolling down a rough wedge which lying on a smooth surface

A sphere of mass $m$ and radius $r$ rolls down from rest on an inclined (making an angle $\phi$ with the horizontal ) and rough surface of a wedge of mass $M$ which stays on a smooth horizontal floor. ...
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### Projectile Motion with air Resistance - Adjust only the Angle to hit a target

OK, let me preface this by saying i am not a physics student, nor have i ever been. I am a software engineer working on a development degree. So this is homework but the assignment was just to create ...
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### CPT invariance of Dirac equation

We know that Dirac equation is $$( i \partial _\mu \gamma ^\mu - m ) \psi ~=~0.$$ How can we show that Dirac equation is invariant under CPT transformation?
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### Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
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### Help with ideal gas law manipulation

Equation 1 represents an improvement over the intial assumption of constant mass velocity (i.e., $\rho v=\rho_o v_o$). We can now improve Eqn. (2) to get to Eqn. (3). My question is: what are the ...
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### Defining axes for conservation of energy [on hold]

Problem: A bungee-cord jumper is on a bridge that is $y_1$ above water level $y_2$. The bungee cord obeys Hooke's law with spring constant $k$ and has a relaxed length $L$ The jumper stops before ...
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### Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
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### How much inductance and capacitance generate in copper strip? [on hold]

I have 60m long copper strip and cross-section area of 25mm x 3mm. and also it has some 90 degree turn after 10m distance. So, How much inductance and capacitance will be generated in strip.? and we ...
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### Which ball touches the ground first?

This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes ...
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### Error in Standard Textbook “An Introduction to Quantum Field Theory” of Peskin and Schroeder?

On page 191 there is a equation for $D$ given by $$D=x(k^2-m^2)+y(k'^2-m^2)+z(k-p)^2+(x+y+z)i\epsilon. \tag{6.43}$$ With $k'=k+q$ and the constraint $x+y+z=1$. Also $p^2=p'^2=m^2$ and maybe $q=p'-p$. ...
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### Fourier Transform of Poisson Equation [migrated]

While trying to solve the Poisson Equation by using Green's Function I have to Fourier transform the equation i.e $$-\nabla^{2}\phi(r)=\rho(r).$$ In the book after Fourier transform, the solution ...
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### Satellites and gravitation

A satellite with mass $m$ orbits a planet of mass $M$ in a circular path with radius $r$ and velocity $v$. Due to some internal technical failure, the satellite breaks into two, similar parts with ...
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### Potential Energy and Kinetic Energy [on hold]

how does potential energy related to height? how does kinetic energy related to velocity? how does potential energy related to those kinetic energy? how does potential energy and kinetic energy ...