# Questions tagged [homework-and-exercises]

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-like questions.

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### How will Decreasing Velocity Affect Time Dilation? [duplicate]

Imagine that we have two observers, named $O_1$ and $O_2$. $O_1$ is traveling at a velocity of $\frac{c}{2}$ for $60$ seconds while $O_2$ is completely still. According to the equation for time ...
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### How do I calculate the maximum separation between a chord and arc when I only know the length of each? [migrated]

If I know the length of a chord and I know the length of an arc that both have the same starting and ending points (A and B), how do I calculate the maximum separation between them? (D and D1) What is ...
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### Proof that $U$ is an unitary operator [closed]

I have a function $f$ mapping a bit onto another bit, i.e. $f : \{0, 1\} \rightarrow \{0, 1\}$. The function f is either constant, so f(0) = f(1) or balanced, so f(0) $\neq$ $f$(1). The quantum gate ...
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### Why can we add in new things into system such that we have symmetry, exploit the symmetry and cancel out the fact that we added more things in end? [closed]

A cube made of insulating material has uniform charge distribution throughout it's volume. Assuming electric potential due to this charged cube at infinitely distant places to be zero, potential at ...
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### How much energy is required to boil and maintain boiling water temperature for a set time period?

I am trying to calculate the amount of energy required to bring 1 litre of water up to boil (from 20 degrees C to 100 degrees C) and to maintain the water temperature at 100 degrees C for a period of ...
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### How can I find the canonical transformation? [closed]

The Hamiltonian is $H=\frac{p^{2}}{2m}-Fq$, where $F$ is constant The transformed Hamiltonian is $K=P$ How do I find the canonical transformation? I know that $\dot{Q}=\frac{\partial K}{\partial P}=1$ ...
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### How to infer about the volume of the body from measuring the mass of the object in 2 different liquids?

While solving a problem on hydro statics subject I saw a statement that argued that if I know the weight of the object in the air and then I know the weight of the object in the water.so when I ...
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### Emf, terminal voltage, lost volt & internal resistance

When we insert neutral copper and zinc electrode in a battery containing $H_2SO_4$ the acid splits up.The hydrogen ions move towards the copper plate and the sulphate ions move towards the zinc plate....
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### Double pendulum equations of motion using Newton's laws [closed]

I need help to understand this problem taken from Mechanical Vibrations by S. Rao I know that the equations of motion could be obtained in various ways, for example using the Lagrangian, but, at the ...
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### Any boundary conditions missing from this problem? [closed]

Recently I was solving some boundary value problems in Electrostatics. I stumbled upon a problem with an infinitely long cylinder (axis along the $z$-direction and radius $a$) with a plate inside it (...
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### Energy Conversion - Potential Energy to Kinetic Energy

In what form and by what way is energy converted when i, say lift a block to a height h above the earth's surface. If the said energy, say 5 Joules, is spent in ...
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### What is the current in the circuit if the LED measures $2$ volts? [closed]

Draw a series circuit with a 6v battery, an LED and a 330 ohm resistor. What is the current in the circuit if the LED measures $2$ volts? I was able to successfully draw the circuit but I am not quite ...
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### Minimum amount of Tritium for fusion reaction producing Tritium

I'm not studying physics. I only worked with basic dynamics and have no idea how to calculate this. It's likely that the answer to the question I'm asking is nonsensical, but, from my point of view, ...
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### Change in ammeter's indication due to change in resistance [closed]

I stumbled on a problem in a textbook, where I was asked to describe the change in ammeter's indication due to change in resistance in circuit: rheostat's slider is moved or key is locked as indicated ...
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### Capacity of a capacitor with multiple dielectrics [closed]

The question that I have is how should I calculate the total capacity of the capacitor described in the picture below: I tried taking Air, $C_1$,$C_2$ as parallel capacitors (They should have the ...
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### How to derive the 2D asymmetric form of free Green function at large distance?

The free Green function: $$G(k)=\frac{1}{k^2+r}$$ I want to derive its form in real space(assuming the most trivial Euclidean metric) : $$G(x)=\int d^D k \frac{e^{-ik\cdot x}}{k^2+r}$$ for two-...
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### Electron Plasma Frequency

Displayed is the context My question is, why doesn't the electric field from the electrons permeate throughout the cold plasma? Surely there will be flux on the RHS of the boundary as there is an ...
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### What happens if I increase the magnitude of the centripetal force? [duplicate]

Suppose that a particle is in uniform circular motion and the magnitude of the centripetal component of the net force increases. Does this increase the tangential speed or decrease the radius of the ...
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### Is 13 really the answer for the “Devil's problem” in physics (a rolling tube with a rod)? [closed]

Recently I chewed the fat with a physics student and got intrigued by him mentioning "the Devil's problem," which he described as a simply worded mechanics problem that is extremely ...
In the following question, the capacitor $C_2$ is is initially charged to a potential difference to $2\epsilon$, when the switch was open. The solution to the problem takes the rate of change of ...
Let's think that there is a black hole with mass $M$ and matter with mass $m$. Two objects have distance $R$. What is the gravitational potential energy between the black hole and the mass? How can I ...