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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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17 views

Help with question regarding Maxwell distribution law for velocity of gases [on hold]

Here is the question. I have succesfully completed the first question where I had to find out the equilibrium distribution of molecular translational energies. But i'm not able to get the second ...
0
votes
0answers
16 views

The potential energía of a pendulum attached to a vertical spring

I have the next problem about lagrangian mechanics: A particle of mass $m_1$ is suspended of a vertical spring of constant $k$ and natural length $l_0$. A second mass $m_2$ is attached to the first ...
1
vote
1answer
27 views

Simple Hamiltonian in curved space-time

Consider the theory of a free massless scalar field with a non-trivial background metric: $$ \mathcal{L} = -\sqrt{-g} \left( \frac{1}{2}\partial_\mu \phi \partial^\mu\phi\right) .$$ (I prefer the '...
1
vote
0answers
29 views

Quantum Scalar Field Theory with cubic and quartic interaction

If I have a scalar Lagrangian with and interaction term given by cubic and quartic terms (so a scalar theory + $φ^3+φ^4$ interaction), what are the possible divergent 1PI diagrams at one and two loops?...
-2
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0answers
22 views

Confusing Collision problem with Inclined plane [on hold]

I do not understand where am I going wrong in Question number 13 This is what I did But the answer is $\frac{mu\sin^2(a)}{M+m\sin^2(a)}$
0
votes
0answers
21 views

Finding the force between magnetized object and conductor

Let's suppose we have an object with some constant magnetization $\vec{M}$ (for example, a cylinder). If we approach it to a material with infinite permeability (i.e. a ferromagnetic) we know from ...
1
vote
0answers
28 views

Vibrational Question [on hold]

A friend recently asked me this question, which I am not even sure how to comprehend... Three masses are arranged at the vertices of an equilateral triangle and are connected by springs along the ...
0
votes
1answer
32 views

How to calculate electrostatic potential at a point w.r.t an ensemble of point charges?

Given an ensemble of charges, how to derive the electrostatic potential at any point due to the ensemble? For example, consider six point charges, each approaching the origin along the three co-...
0
votes
2answers
50 views

Differential equations for the LC circuit

On wikipedia one can find that the DE for an LC circuit is given by $$\ddot I+\frac{1}{LC}I=0$$In one of my papers however I found the equation $$\ddot Q+\frac{1}{LC}Q=0$$ and I've been confused by ...
-2
votes
0answers
30 views

Work done against electric field [on hold]

If a charged body has $10^{-4}$ C charge and radius of $1 m$ then find the amount of work done against the elctric field in contracting the body for $0.5$ m radius. I am fed up with the question.I am ...
-3
votes
1answer
32 views

Which direction the currect will flow?

I know if there is no R3 and R4, the R2 will be short circuited (Current most likely flow through the circuit that has smaller resistance). My confusion is, if the R3 and R4 are there, should we short ...
-4
votes
0answers
18 views

A balloon is descending with 10m/s. When it is at 100m from the ground, a stone is thrown. Calculate the velocity of the stone at 20sec [on hold]

Assumed initial velocity of the stone to be 10m/s and found that it would cover 100m in about 3.585 seconds. But, the question is asking its velocity at 20sec.
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votes
0answers
15 views

It is about Electrostatic Problem in electric field,flux [on hold]

Two point charges 16nC and 8nC are situated at the corners B and C of an equilateral triangle of side 0.03m. Find the magnitude and direction of the resultant electric field at the vertex A of the ...
-1
votes
0answers
19 views

Electric field on dipole with different directions [on hold]

Griffith's E&M problem 4.5 page 165 In the figure p1 and p2 are perfect dipoles a disantce r apart. What is the torque on p1 due to p2.? Wjat is the torque on p2 due to p1? well i calculated ...
-3
votes
0answers
16 views

Physics Elecromagnetic Induction [on hold]

A series combination of L and R is connected to a battery of emf E and negligible internal resistance; then the final value of current depends on : Options: 1. L and R 2. E and L 3. E and R 4. L, R ...
2
votes
1answer
39 views

How to obtain the quantization of a simple pendulum using Bohr-Wilson-Sommerfeld rule? [on hold]

How to obtain the quantization of a simple pendulum using Bohr-Wilson-Sommerfeld rule?
-2
votes
0answers
33 views

How to find the efficiency of a pulley system [on hold]

Find the efficiency of a pulley system which has a mechanical advantage of 2.5 and where the lond lifts by 2.5 meters on pulling the rope by 10 meters. I have never done any problems related to the ...
-1
votes
0answers
32 views

A material point of mass m slides on a curve [on hold]

Can someone help me solve this question, please? In the Oxy plane, where the axis Oy is vertical and oriented upwards, a material point of mass m slides on the curve xy = 1, 1/2 ≤ x ≤ 2, under the ...
0
votes
0answers
21 views

Finding the Buoyancy force acting on the piece of aluminum

I have problem finding the Buoyancy force acting on the piece of aluminum. Problem to solve A 0.48 Kg piece made with aluminum is immersed in water. Find the Buoyancy force acting on the piece of ...
1
vote
1answer
62 views

Question on Partial Differentiation in Thermodynamics

For energetic fundamental relation $U=U(S,X_1,\ldots)$ where $X_k$ represent extensive parameters $V$ or $N_j$, let \begin{equation}P_k=\frac{\partial U}{\partial X_k}.\end{equation} For entropic ...
0
votes
1answer
47 views

Energy formula for finite potential well [on hold]

The energy formula for infinite potential well is $$E=\frac{n^2h^2}{8ma^2},$$where $m$ is the mass of the particle, $a$ is the width of the well but in the case of finite potential well, I actually ...
-4
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0answers
18 views

rotation dynamics angular momentum [on hold]

please solve this rotation mechanics question 19,20 and 21
0
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0answers
34 views

The flip of the spin (Problem 11.6(b) in Schwartz's QFT)

I am asking a question regarding the following problem: For the non-relativistic limit, choose explicit spinors for a spinor at rest. Show that $\bar\psi_s\gamma^\mu\psi_{s'}$ vanishes unless $s=s'...
-1
votes
0answers
11 views

Magnification of a system with only index of refraction given? [on hold]

Hello StackExchange community, I have an issue with the following problem: A laser beam-expander is to be designed in the form of a non-inverting Galilean telescope (i.e. with one negative and ...
0
votes
0answers
17 views

Drift-diffusion equation with no-flux boundary condition [on hold]

I know that the solution for the below equation $$\partial_t f(x,t)=D \partial_x^2 f(x,t)+ \partial_x f(x,t)$$ with initial and boundary conditions: $D\partial_x f(x,t)+f(x,t)=0$ at $x=0$ and $f(x,...
-2
votes
2answers
30 views

Finding the value of $r$ for which the radial function, $P(r)$, has a maximum? [on hold]

In my (university) particle physics course, I am asked to find the values of $r$ for which the function $P(r)$ of a $2s$ Hydrogen electron has its maximum values. Here, $r$ denotes the distance in ...
0
votes
3answers
45 views

Does change in the centre of gravity affect weight and if so how? [on hold]

A mason on a ladder standing in a pit of mud realises that as he scales up the ladder it starts to sink whereas at his original position ( bottom of ladder) it did not sink. Explain how without ...
9
votes
3answers
1k views

Simple Question About Conservation of Angular Momentum

Lately I encountered a question in my physic book very simple looking but I can't understand why what I am thinking is wrong because I didn't satisfied from the right answer showed in a video about it,...
-2
votes
0answers
28 views

Express work in terms of linear thermal expansion? [on hold]

I have the following problem. Below are two approaches that came up as a solution. the second one is not mine. I feel confused by the question.I need helped in answering the problem. here it should be ...
2
votes
1answer
78 views

What is the closed form of the following integral?

I want to know the closed form of the following master integral in (any) $D$ dimension \begin{equation} \int\frac{d^D k}{(2\pi)^D}\frac{1}{k^2(k+r)^2(k+p)^2}. \end{equation} The references that I can ...
0
votes
1answer
15 views

Net flux through insulating cylinder

In a non-uniform electric field, say with field lines curving away from each other along x, will the net flux on a cylinder be negative or zero?
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0answers
21 views

What is the height of the air bubble relative to the surface of the liquid? [on hold]

I am wondering about the question above. I understand how to calculate the pressure of the gas, but am not calculating the correct answer for the second part (question 9) that asks about the height of ...
-2
votes
0answers
19 views

Moments and Equilibrum [on hold]

Q: A uniform cylinder has height 10.0cm and diameter 3.0 cm. The cylinder is placed with its circular base resting on a horizontal table. Calculate the maximum angle through which it can tip before it ...
0
votes
2answers
48 views

Finding partial molar volume from an algebraic expression

I'm given the equation $ V = 120X_1 + 70X_2+X_1X_2*(15X_1+8X_2)$ and told to calculate $\bar V_1 $ & $ \bar V_2$ and then to show that $ V = \Sigma_i X_i*\bar V_i$. Since there are two mol ...
2
votes
3answers
62 views

Centripetal Force Formula Confusion

After I finished studying and trying to test my knowledge to see what I have learned, I realized I am confused about the centripetal force formula: $$F_c= \frac{mv²}{R}$$ which I know is also equal to ...
0
votes
1answer
52 views

Where is the location of centre of gravity of the Earth? [on hold]

Take the Sun as a point object at the origin. Take the Earth as a sphere centred at $x=d$ with a radius of $R$ Let $d=150,000,000,000$ m Let $R=6,400,000$ m Slice the sphere into vertical disks of ...
0
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0answers
24 views

Operational Equalities [on hold]

How to check the following operational equalities: $$ x^2\dfrac{d}{dx} \dfrac{1}{x}=x \dfrac{d}{dx}- 1 \quad \& \quad \left( x +\dfrac{d}{dx} \right)^2= 1 + x^2 +2x\dfrac{d}{d x} + \dfrac{d^2}{d ...
-2
votes
0answers
38 views

Heat engine problem, not sure how to start [on hold]

I do NOT want homework help. I simply need some direction on how to start to solve part A. I tried everything to try to start but couldn't get anywhere near the answer. What am I missing here? I tried ...
-1
votes
1answer
36 views

Moment of inertia and torque [on hold]

Why there is different moment of inertia with respect to point P about which a rigid body is moving around a circle with some velocity and spinning about its own axis compared to the one which is just ...
0
votes
0answers
31 views

Van der Waals fluid: density fluctuations [on hold]

I am given the following problem: Consider a region of spatial extent L (and with volume $L^3$) within a Van der Waals fluid given by the equation of state \begin{align} \beta p = \rho/(1-b\rho) ...
7
votes
2answers
264 views

Force needed to pull an end of a bended carpet lying on a floor with constant speed [on hold]

Consider this system. A long, thin, pliable carpet is laid on a floor. One end of the carpet is bent back and then pulled backwards with constant speed $v$, just above the part of the carpet which is ...
1
vote
0answers
23 views

RG of 2D Ising with nonzero magnetic field on triangular lattice

I am given the Ising Hamiltonian \begin{align} H = K \sum_{<ij>}S_i S_j + h \sum_i S_i, \quad K>0 \end{align} to set up a real-space block-spin RG, where the renormalized spins are ...
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0answers
40 views
0
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0answers
13 views

Wave in a turning fork [on hold]

When two turning forks are excited in a certain gaseous medium they produce wavelengths of 100cm and 101cm. Calculate the speed In m/s of sound in that gas if the turning forks produce 7 beats every 2 ...
-1
votes
0answers
13 views

Find rate of change of radius [on hold]

A balloon of radius $20 cm$ is given uniform charge $2×10^{-6}C$. The mass of the balloon is $90g$. The balloon is now released. Determine the rate of change of its radius when the radius reaches ...
-1
votes
1answer
28 views

Trouble in deriving component of acceleration [on hold]

Q) A smooth ring A of mass m can slide on a fixed horizontal rod. A string tied to the ring passes over a fixed pulley B and carries a block C of mass M ( = 2 m) as shown in figure above. At an ...
0
votes
0answers
28 views

Oscillating rod about the vertical axis [on hold]

Consider the following situation, A rod is attached to two identical massless strings with a length of $R$. The rod is then given a small kick so that it goes back and forth around the vertical axis. ...
-3
votes
0answers
23 views

Finding Minimum Time [on hold]

Here's the problem: What I did: So basically I used some geometry to to get $l_1$ and $l_2$ in terms of $r$ and the assumed angle $y$. Now, I assumed that if the ant can climb straight up at a ...
0
votes
0answers
28 views

Grounded Conductor [on hold]

The inside of a grounded spherical shell of radius $R$ is filled with uniform charge density $\rho$ and charge $Q$. (The density is fixed; it doesn’t "exit to ground".) What will be the electric field ...