# 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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### Tension on a string between two objects on a friction less surface [closed]

I just need my work checked here. Please let me know if I am correct. I had this problem in one of my test in which I did not get full credits. I am re-doing this(hopefully correctly this time) just ...
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### Equation of motion for a falling rod (with one end touching a frictionless surface)

I have a quick question about the equation of motion for a falling rod (with one end touching a frictionless surface). The end touching the surface is not fixed. I am given the moment of inertia about ...
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### Deriving commutation relations in second quantisation

I am trying to start from: \begin{align*} [\phi(x),\pi(x')] = i\hbar\delta(x-x') \\ [\phi(x),\phi(x')] = [\pi(x),\pi(x')]=0 \end{align*} to derive: \begin{align*} [a(k),a(k')^\dagger]=\delta_{kk'}\\ ...
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### Kirchoff Loop and current

The pic of the circuit/problem: I got the problem right, but i want to make sure my reasoning is correct for the current left of the 2.1 V battery. Its the same current as $I_1$ because the ...
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### Rotation of angular momentum eigenfunctions?

I am struggling to understand this apparently obvious example in my group theory notes: Where do the $e^{i\phi}$ and $e^{-i\phi}$ factors come from? I know that the $m_l$ = -1,0 and +1 angular ...
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### Solving actual weight lifted

I was wondering if anyone knew the formula to calculate how much force is required to lift a tire or any object by the edge. For example if a tire weighs 500 lbs (or has a mass of 226.8 kg). I would ...
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### The best way to cool the teapot

My professor today in the class made us a question: "Lets say we have a teapot with water in it.The water is hot.Now we want to cool the water. Will it cool faster if we put an ice cube above the ...
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### Colors in the secondary rainbow reverse of that in the primary rainbow

Why the colors of Secondary rainbow is reverse of that in the color in the Primary rainbow? What can be the possible reason among the following options Because it is formed by one internal ...
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### Determining the horizontal position of an object [closed]

In my calc-physics class we were given the following question: A movie stuntwoman drops from a helicopter that is $30.0 m$ above the ground and moving with a constant velocity whose components are ...
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### In what situations do water levels not reach equilibrium?

I have been taught that water levels will always equal out. However, now I find that sumps and some other setups allow for water not to become equal. What other arrangements allow for the water levels ...
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