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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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0answers
27 views

Orbit velocity is this question ill defined [on hold]

I am attempting to solve this question but I feel that the question may be ill defined. The question is in two images, the first image and second image. I have tried many attempts at this. The ...
-1
votes
1answer
27 views

Equivalent resistance in triangle

How do I find equivalent resistance between A and B? I'm not sure which resistors to connect, and how, parallel or in series.
0
votes
1answer
22 views

Hyperfine structure of hydrogen

I have an expression $H=a \vec{I} \vec{S}$ which is a leading term in Hamiltonian for the hyperfine structure of p-states in hydrogen, but I don't really understand it. By Wigner-Eckart, hyperfine ...
0
votes
0answers
11 views

Solenoid and circular loop, mutual inductance

I have to solve this physics problem: Consider a solenoid with N turns per unit of length and a circular loop, both of radius a. These, are placed one after the other, in a coaxial form, separated a ...
0
votes
2answers
35 views

Collision & Work

Let's assume there is an unusual guy and whenever he is shot, the bullets actually jump off of him towards the opposite direction, in the x-axis. I need to find the work applied by the guy per minute ...
0
votes
0answers
22 views

$y$-component and $z$-component not equal to zero

If we were to place a point on the perpendicular bisector of an evenly charged rod of positive charge, lying along the y-axis, By symmetry are there any other ways that the electric field's y and z ...
1
vote
0answers
35 views

Finding the Ricci tensor components for the Schwarzschild metric

I'm trying to use Cartan's method to find the Schwarzschild metric components from Hughston and Tod's book 'An Introduction to General Relativity' (pages 89-90). I'm having problems calculating the ...
-1
votes
0answers
13 views

A particle moves on the outside of a smooth ellipse in a vertical plane.The major axis of the ellipse is vertical & its eccentricity is e [on hold]

A particle moves on the outside of a smooth ellipse in a vertical plane. The major axis of the ellipse is vertical & its eccentricity is $e$. If the particle starts from rest from the highest ...
0
votes
1answer
17 views

Magnetic moment of a radially symmetric current

In my latest assignment I'm tasked with finding a magnetic moment $\mu$ of a hydrogen atom, whose current distribution $\mathbf{j}(\mathbf{r})$ looks like $$\mathbf{j}(\mathbf{r})=\frac{e\hbar}{3^8 \...
0
votes
0answers
16 views

Showing that a locus is a sub-manifold [on hold]

I'm self-studying differential geometry using Frankel's ``The Geometry of Physics". The first problem (1.1(1)) is about determining whether or not the locus $$x^2+y^2-z^2 = c $$ is a submanifold in $\...
0
votes
1answer
43 views

Is it appropriate to neglect the gravitational force on the electron? [on hold]

Compare the weight of the electron to the magnitude of the force on the electron. Is it appropriate to neglect the gravitational force on the electron in example these example $mg= 8.93 \times 10^{-...
-1
votes
0answers
14 views

Electric Charge and Electric Field [on hold]

A particle with positive charge Q is held at the origin. A second particle with positive charge q is fired at the first particle and follows a trajectory as shown in Figure 22-28. Is the angular ...
-2
votes
0answers
14 views

Comparing luminosities [on hold]

A central star is found to be an M type star. Using the typical temperature of an M type star and assuming it has the same diameter as the Sun, compare its luminosity with that of our sun. Our sun ...
-1
votes
0answers
16 views

Determine the mass of a central star? [on hold]

An earth-like planet orbits its central star at a distance of 2AU in a time of 4 years. Determine the mass of the central star in solar masses. "a" cubed is 8 and "p" squared is 16 which is not ...
-3
votes
0answers
19 views

Vector addition in electric charge on plane [on hold]

in example 21.4 suppose the point charge on the y-axis at y=-.30 m has a negative charge -2micro Coulomb the other charges remaining the same. Find the magnitude and direction on the net force on Q. ...
0
votes
1answer
32 views

How to use General Energy Equation in parallel pipes?

My question comes from exercises with parallel pipes such as this. I know that to analyse internal flow, we use general energy equation which origins from the 1st law so each time we apply it we are ...
-3
votes
0answers
50 views

When is $a = αr$ not valid? [on hold]

Under what conditions does the relationship $a = αr$ not apply? Would this equation be valid for a rolling soup can? a: linear acceleration α: angular acceleration r: radius of the object
0
votes
1answer
41 views

Ambiguous curl for a vector field

I'm trying to work out how to explain why the curl/divergence for the following image is ambiguous without giving the explicit vector function for the following: E has an ambiguous divergence and I ...
0
votes
1answer
22 views

Falling object and the side wind

I don't have a big knowledge on Physics so I'm sorry in advance if it doesn't make sense.. If a brick is falling from 100m tall-building when there's the side wind of 30m/s, is there any way I can ...
-3
votes
0answers
12 views

Solve this question from rotational mechanics [on hold]

I would like to have a detailed solution.Please help.
0
votes
0answers
21 views

Generating functional for amputated connected Green functions

As I understand, generating functional for amputated connected Green functions is exatly $\mathcal{S}$-matrix of theory. One can represent this functional as (for instance, $\phi^3$ theory): $$e^{\...
2
votes
2answers
48 views

Coordinate transformation for a comoving frame for abitrary trajectory

Let's suppose there is a particle moving through space time. It moves along the x-direction with a time dependent velocity. Seen from an inertial frame it has the velocity $v(t)$ where $t$ is the ...
-1
votes
1answer
26 views

Center of mass vs. gravitational potential [on hold]

Suppose that there exists 3 bodies in space. Two are separated by a great distance $d$, both have a mass $m$, and the two have a center of mass $P_{cm}$. If I imagine a "probe" mass near $P_{cm}$ of ...
-3
votes
0answers
23 views

Energyeigen modes of a vibrating string [on hold]

Energyeigen modes for the vibration of a string fixed at both ends plucked at the middle
0
votes
0answers
9 views

Electric dipole [on hold]

Two small plastic spheres are given positive electrical charges. When they are 15.0 cm apart, the repulsive force between them has magnitude 0.220 N. What is the charge on each sphere a.) if the two ...
-2
votes
0answers
11 views

Find the magnitude and the direction of net force $Q$ [on hold]

suppose the point charge on y-axis at y=-0.3 m has negative charge-2.0 C the other charges remaining the.same. find the magnitude and the direction of the net force Q. how does your answer differ from ...
-1
votes
0answers
32 views

Tension of a rope [on hold]

Say we have a mass attached to two strings, A and B. The angles are not equal. And A is larger in length compared with B The m = 60kg, θ= 60° and Ø= 35° If rope A is 7m long, what would the tension ...
-3
votes
0answers
20 views

Does the maximum permissible current depend on the length of the wire? [duplicate]

The greater the diameter of the wire used in household wiring, the greater the maximum current that can safely be carried by the wire. Why is this? Does the maximum permissible current depend on the ...
-3
votes
0answers
22 views

Electric field of magnitude and direction [on hold]

A small object carrying a charge of -55.0 micro coulombs experiences a downward force of 6.20*10^-9 Newton when placed a a certain point in an electric field. a) what are the magnetic and direction ...
-2
votes
0answers
18 views

Electric field calculation [on hold]

Near the earth's surface, the electric field in the open air has magnitude 150N/C and is directed down toward the ground. If this is regarded as being due to a large sheet of charge lying on the earth'...
2
votes
1answer
55 views

Beat frequency with tuning forks

If you have two tuning forks and you know that one tuning fork is 305 Hz, and when the tuning forks are pinged together you get a beat frequency of 6 Hz, then you know that the other tuning fork is ...
-2
votes
0answers
22 views

Applied Electric Field [on hold]

Two parallel-plate vacuum capacitors have plate spacings $d1$ and $d2$ and equal plate areas $A$. Show that when the capacitors are connected in series, the equivalent capacitance is the same as for a ...
1
vote
0answers
47 views

Total number density of galaxies and problematic expression in practise

I am asked to give the formal expression of the total number density of galaxies and explain why is this expression problematic in practice. From what I saw from my research and into my lectures, I ...
-4
votes
0answers
35 views

F=ma 2017 Question 5 [on hold]

I have been working on this problem but keep getting answer choice A.
-4
votes
0answers
19 views

field of electricity [on hold]

A small object carrying a charge of —55.0 μC experiences a downward force of 6.20 X 10-9 N when placed at a certain point in an electric field. a) What are the magnitude and direction of the electric ...
0
votes
1answer
31 views

Calculate work of a given force [on hold]

We want to calculate the work of a force $F=(x-y,x,\sqrt{z})$ on the curve $(x-3)^2 + y^2 = 1, z = 3$ from the point $(3,-1,3)$ to the point $(2,0,3)$. First I thought about doing this in polar (...
-2
votes
0answers
24 views

Electric field Calculations [on hold]

The electric field due to an infinite line of charge is perpendicular to the line and has magnitude $E=\frac{2}{\lambda r}$. Consider an imaginary cylinder with radius $r= 0.250\ \text{m}$ and length$...
0
votes
0answers
23 views

Phase difference [on hold]

Considering two spring-and-block harmonic oscillators set up side by side with identical spring constants and block masses, if we observed that the blocks' positions were the same (moving in opposite ...
-1
votes
0answers
14 views

Potential difference that is established between parallel plates in air [on hold]

A potential difference of 4.75 kV is established between parallel plates in air. a.) If the air becomes electrically conducting when the electric field exceeds 3.00×10 power of 6 v/m, what is the ...
0
votes
0answers
30 views

Need help with harmonics and fundamental frequency [on hold]

This is a question my professor gave: A flute and clarinet player begin to play from the same music score. They quickly realize they are playing different notes, because a clarinet is a transposing ...
-4
votes
0answers
10 views

Each square centimeter of the surface of an infinite plane sheet of paper has 2.50 x 106 excess electrons [on hold]

Each square centimeter of the surface of an infinite plane sheet of paper has 2.50 x 106 excess electrons. Find the magnitude and direction of the electric field at a point 5.00 cm from the surface of ...
-2
votes
0answers
18 views

Capacitors and dielectrics [duplicate]

A parallel-plate capacitor is connected to a power supply that maintains a fixed potential difference between the plates. If a sheet of dielectric is the slid between then plates.what happens to i) ...
-2
votes
0answers
24 views

how to solve this big problem for me [on hold]

I am very confused about this question, I wish someone can help me to solve the second question in this.
-1
votes
0answers
17 views

Electric charge [on hold]

In a physics lecture demonstration in a charge of -0.180 uC is placed on the spherical dome should you sit for the electric field at your location to be within the recommended maximum of 614 N/C. ...
-4
votes
0answers
32 views

Why do we not time travel? [on hold]

Why is it bad to time travel. Time travel is science fiction but what if it really happened we would have many dangerous things to deal with. The future and past dinosaurs ww1 the Great Depression. ...
-2
votes
1answer
21 views

Potential difference across the ends of a conducting rod kept in a varying magnetic field, Why a time varying magnetic field develops induced emf [on hold]

Why a time varying magnetic field induces emf in a rod? This can be explained with the help of a question: A conducting rod of length 'l' is kept in a time varying magnetic field as shown in the ...
1
vote
0answers
23 views

Satellite radiance measurements in spectral regions

Q: A satellite measures longwave radiation emerging from a planet with uniform surface temperature T1 and uniform atmospheric temperature T2. What values of radiance does the satellite measure in the ...
0
votes
0answers
13 views

How to find equivalent inductance in the following image [on hold]

I know how to apply Kirchoff Rules. I am unable to simplify the circuit to find any symmetry.
1
vote
0answers
14 views

Unitarity violation: sign inconsistency in Quigg

In Gauge Theories of the Strong, Weak, and Electromagnetic Interactions, C. Quigg explains how the process $\nu \overline{\nu} \rightarrow W^+ W^-$ violates unitarity at high energy unless we add the $...
0
votes
1answer
40 views

Problem with converting Integral to Gamma functions (from HQET heavy quark self-energy diagram)

In the calculation of HQET radiative correction, I came across the Equation: $$\int_0^{\infty}d\lambda ~ \lambda^{-\epsilon}(\lambda+\omega)^{-\epsilon} = \frac{1}{2\sqrt{\pi}}\Gamma(\epsilon-\frac{1}{...