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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2
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2answers
23 views

How come in free fall you feel weightless even though gravity is pulling down on you?

How come in free fall you feel weightless even though gravity is pulling down on you? (ignore air resistance when answering this question).
0
votes
0answers
8 views

What frequencies is radation being emited in infinite potential well

The problem that I am working on is. Consider an electron in an infinitely deep one-dimensional potential well of width 1nm . This electron is prepared in a state that is an equal linear ...
1
vote
1answer
11 views

Transformation of self-dual and anti-self-dual tensors and irreducibility of representations

I am working out exercise 2.5 of Maggiore's book. Part of the exercise is the following: Verify that self-dual and anti-self-dual tensors are irreducible representations of (real) dimension three of ...
0
votes
0answers
81 views

Do I need to consider the spin of electrons when they are in infinite potential well

This is the problem I have And this is one of my books tell me what should I do And my question is: Do I need to consider spin in this case?(that is, I don't think the book is right...) I found ...
3
votes
0answers
29 views

Elastic collision / relative velocity problem [on hold]

I'm having some trouble with a homework exercise and I'd really appreciate some help! I've done the first part correctly (according to the solution sheet), but I can't seem to get the second part ...
-3
votes
0answers
28 views

De-broglie wavelength [on hold]

The de-broglie wavelength of an electron emitted from the ground state of an H-atom after the absorption of a photon equals 1/2 of the de-broglie wavelength when it is in orbit. The energy of the ...
1
vote
2answers
41 views

How does a point charge interact with a Gaussian surface?

A spherical Gaussian surface encloses a point charge $q$. The point charge is moved to to a point away from the center of the sphere. Does the electric field at a point on the surface change? ...
1
vote
1answer
30 views

Calculation Equivalent Resistance In A Circuit With resistances connected in a circle

I am having trouble in finding the equivalent resistance between the terminals 'a' and 'b' in the following circuit: Please can anyone explain to me how to solve such problems. Thank You!
1
vote
0answers
21 views

How can you find the $u$ using time dilation if you only know $\Delta t_o$?

I've come across two problems dealing with time dilation now that ask how fast should an astronaut go in order to travel EG: 400 LYears in 10 Years. What I can not wrap my head around is how this is ...
2
votes
1answer
27 views

A couple of questions regarding work to velocity exchange

I was tasked to express the velocity of the cube of mass $m$ at point B using the constants given in the picture below. Friction could be ignored, and the cube could be presumed to reach B with the ...
-4
votes
0answers
24 views

Problem - Escalator [on hold]

I need help in resolving the following problem: On a recent weekend, Anna was rushing through a shopping centre doing her shopping she had occasion to use the escalator 3 times. The first time the ...
-2
votes
1answer
43 views

Bohr radius question

I'm doing a homework problem where it asks to calculate the diameter of a hydrogen atom with $n=600$. I used the equation $r=\frac{n^2a_0}{Z}$ where $a_0=0.529e^{-10}m$. Solving for $r$ yields: ...
1
vote
0answers
28 views

Relativity Mapmaking in spacetime

The problem as stated: I do not know how I am supposed to map this. The instructions don't make sense to me and the textbook is really un-helpful. This is the map that I have to draw this on. I ...
0
votes
1answer
23 views

Simple Harmonic Motion given velocity and acceleration

I am trying to understand how to relate velocity and acceleration of an object to it's amplitude, period, and frequency given only the following: An object of mass m=20kg moves with SHM along the ...
0
votes
0answers
17 views

finding work done by the buoyant force on a submerged object [on hold]

A flotation device is in the shape of a right cylinder, with a height of 0.500 m and a face area of 4.00 m2 on top and bottom, and its density is 0.320 times that of fresh water. It is initially held ...
1
vote
1answer
20 views

Why is a series resistor needed in a simple thermistor experiment? [on hold]

I have come across the following simple question, however I can't see any need for a fixed resistor in series. The only possible reason that I can think of is that the resistance of the thermistor ...
0
votes
0answers
22 views

Calculate the Bohr radius of a muonic atom

I want to better understand this problem and how to calculate the Bohr radius. The equation I found in my book is $r_n=\frac{n^2 \hbar^2}{mkZe^2}=\frac{n^2a_0}{Z}$. However, I found a problem online ...
0
votes
1answer
25 views

Methods to solve a vapor pressure equilibrium question with water on the moon?

"Imagine a tall column of water on the Moon, maintained at a temperature of 50°C and left to the open vacuum at the top. Up to what depth will the water continue to boil? The Moon's radius is 0.273 ...
0
votes
0answers
18 views

One from Landau's Minimum (Macroscopic Electrodynamics)

A dielectric sphere with the electric and magnetic susceptibilities ε1 and µ1 is rotating with angular frequency ω in a constant electric field E~ in a medium, characterized by the parameters ε2 and ...
0
votes
1answer
17 views

a question on work and kinetic energy [on hold]

A bullet has a mass of 0.02kg and is moving with a speed of 10m/s. It can penetrate 10cm of a given target before coming to rest. If the same target is only 6cm thick, what will be the speed and ...
0
votes
0answers
30 views

meson decay in Yukawa theory

I want to calculate decay width $\Gamma_{i\rightarrow f}$ (under assumption that we don't measure the polarization of particles in final state) in a decay process $$\phi \rightarrow \psi \bar{\psi}$$ ...
0
votes
0answers
21 views

inlet velocity calculation from mass flow rate

I am struggling for following calculation, Could somebody please help me with this Mass flow rate and inlet velocity at 300 K and 40 mbar are 4.246 gm/minute and 32.8 cm/sec respectively, if the ...
1
vote
0answers
10 views

Capacitor charge and current as a function of type question [on hold]

Two capacitors, one resistor and an ideal battery are connected through switches s1,s2 and s3 as shown in figure. Initially capacitor of capacitance 4C is charged, while other is uncharged. The upper ...
0
votes
0answers
17 views

Simple Harmonic Osillator [on hold]

For simple harmonic oscillator, calculate a. The energy b. The mean position c. The mean momentum square d. Standard deviation of position e. Standard deviation of momentum f. Cheek uncertainty ...
2
votes
1answer
44 views

Electric Potential due to Sphere when cavity is at arbitrary position [on hold]

While doing practice question, I came across a question... A solid sphere of radius a has a cavity of radius b which has a uniformly charge distributed with density $-\rho$ and the remaining part ...
1
vote
0answers
11 views

Bullet - Jet problem, How to equate horizontal displacement. projectile motion [on hold]

A jet is moving hotizontal with speed of 720km/h at height 1960m . when it passes above point on ground at same time bullet is fired from that point with velocity 400m/s I want to know the angle from ...
0
votes
1answer
24 views

Find the magnitude of the resultant force which these engines exert on the rocket?

A rocket fires two engines simultaneously. One produces a thrust of 760N directly forward while the other gives a thrust of 484N at an angle 34.0 degrees above the forward direction. What is the ...
0
votes
0answers
25 views

Determinant of block matrix with off diagonals as vectors [migrated]

I've been given an $(n+1)\times(n+1)$ square matrix, which is written in the form of a block matrix with the following dimensions $ \begin{bmatrix} (1\times1) & (n\times1)\\ ...
0
votes
0answers
45 views

Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
1
vote
1answer
41 views

$dU = \sum E_i dp_i + \sum dE_i p_i = TdS - PdV \implies \sum dE_i p_i = - PdV$? [on hold]

This is a formula my professor gave in class, but I'm entirely lost how he arrived at the conclusion (I understand the assumption). Could anyone help me?
1
vote
1answer
22 views

Rutherford scattering: question about impact parameter

http://wonka.physics.ncsu.edu/~blondin/py203/HW5solns.pdf I have a question about the solution to a problem I found online. I don't understand why the author plugs in $\theta=90$ when the question is ...
-1
votes
1answer
22 views

Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= ...
0
votes
1answer
42 views

Vector Addition and Gravitational Forces [on hold]

I was given the following question in my Physics class :- Four particles of masses m, 2m, 3m and 4m are kept in sequence at the corners of a square of side a. What will be the magnitude of the ...
2
votes
0answers
42 views

Use Cartan subalgebra in spinor representation to find weights of vector representation

For $SO(2n)$ we can construct the lie algebra elements by using antisymmetric combinations of $\gamma_\mu$ which obey the Clifford algebra. Up to some prefactor the elements $ S_{\mu \nu} = \alpha ...
0
votes
0answers
19 views

Generators of cubic group: Euler angles

I am trying to build numerically all members of the cubic group in the representation of Wigner D matrices. Angular-momentum quantum number may be small, e.g. 2, so I use the formula stated e.g. at ...
1
vote
2answers
37 views

Free body diagram for two masses on inclined plane with frictions

I'm a bit confused about free body diagrams on inclined planes with frictions. Consider the situation in the picture, where $A$ and $B$ slide togheter on a inclined plane and I want to find a force ...
0
votes
0answers
30 views

A body thrown upwards with some external force [on hold]

A ball of mass of $1Kg$ is held in hand. The moment it is released from hand, without any delay it is hit by an external force of $100N$ in upwards direction. How high will the body go ? If we ...
-1
votes
0answers
27 views

Freely falling body applied some external force [on hold]

A body of mass $10kg$ is thrown upwards with initial velocity = $10m/s$. Then it moves up and falls back down at the same point, after which an external force of $10N$ is applied in the upward ...
1
vote
0answers
26 views

Find the angle of the projectile [on hold]

Given: Hmax = 2 * Range Find the angle of the projectile. After using the formula for both Hmax and Range, I got an angle of 74.69 if I am not mistaken. On the math exam teacher said the answer ...
1
vote
0answers
38 views

Man on a rotating platform [on hold]

A platform rotates in counterclockwise with angular velocity w. A man walks from the center of the platform to the border with constant radial velocity v' wrt the platform. $\mu_s$ is the ...
1
vote
0answers
22 views

Canonical Transformation [duplicate]

How can I prove that the following transformation is canonical: $\begin{cases}\overline{q}_i=\dfrac{q_i}{Q} \\ \overline{p}_i=Qp_i-2Pq_i \end{cases},\ i\in\overline{1,n}$ where $Q=\sum_{i=1}^n ...
0
votes
1answer
34 views

Time-Evolution of a Spin-1 Particle in a Magnetic Field

A spin-1 particle with charge $q$ and magnetic moment $\vec{\mu}=\frac{gq}{2mc}\vec{S}$ is situated in a magnetic field $B=B_0\vec{z}$. At $t=0$ the particle is found in an eigenstate $\hat{S}_y$ with ...
1
vote
2answers
56 views

When does travelling at a fraction of the speed of light appear to the traveler as if they're going the speed of light? [on hold]

If a spaceship is travelling to Proxima Centari, there is a fraction of the speed of light that would make the spaceship appear to reach Proxima Centauri in four years' time. What fraction of the ...
1
vote
1answer
38 views

Figuring out the orientation of a dipole and its distance from a point charge

The problem assigned is this: A dipole is centered at the origin of a coordinate system, and a small charged sphere is some distance away along the perpendicular bisector of the dipole. The particle ...
0
votes
1answer
88 views

Euler's laws - derivation

It looks simple and maybe is easy, but I don't get it. How to obtain the second equality from the first one below? Source: http://emweb.unl.edu/NEGAHBAN/EM373/note19/note19.htm They took ...
4
votes
2answers
45 views

Free body diagram with forces of friction

I'm reallizing that I'm very confused on how to make a free body diagram of forces in some situations where there is friction between two objects. I'll make an example where I cannot figure out what's ...
0
votes
0answers
34 views

Direction of a rectangular vector in two dimensions [on hold]

Assuming the following position vector; R(t) = (2+.4t^2)i + (1.0t)j The function provided yields a parabola, how can I find the specific point in which the angle for the position vector evaluated in ...
0
votes
0answers
37 views

Determining focal length and positions of principal planes [on hold]

I have been stuck on this problem for a few days now, and I am still not confident which approach to take with this question. I am consider using the Gullstrand Equation, but I hear some of my ...
1
vote
1answer
30 views

Help to solve a circuit with capacitor and resistor

Till now I'd never solved a circuit with resistor and capacitor. I'd seen the problem and tried to solve. But now I am in a doubt.The circuit was like that- My attempt-