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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19 views

Quantum mechanical expectation of angular momentum along different axes

This is a question from Concepts of Quantum Mechanics by Mathur & Singh, and I don't know where I should start from: Show that, for a state $|j,m \rangle$, corresponding to a definite value of ...
-6
votes
1answer
24 views

vectors, space and coordinate systems,

An object moves from the position $r_1 = (1,3,-5)$ to the position $r_2 = (-1,4,8)$ during the time $8~\text{s}$. Find displacement, distance, average velocity, average speed.
0
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1answer
41 views

Integral calculation

I do some calculation in QED, but I can not calculate such integral $$ I(a_1,a_2,m_1,m_2)=\int\frac{ d^2\mathbf{x} d^2\mathbf{y}}{(1+\mathbf{x}^2)(1+\mathbf{y}^2)((\mathbf{x}+a_1 ...
0
votes
1answer
61 views

How does one normalize this wavefunction? [on hold]

Here is the question: So I could write $ N = \dfrac{1}{{\sqrt{<Ψ|Ψ>}}} $, right? Considering the parentheses in the exponential term, it looks like a good idea to switch to spherical polar ...
0
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2answers
24 views

Using a charged capacitor to charge two others

Here is the homework question in question: The figure (below) displays a 13.1 V battery and three uncharged capacitors of capacitances C1 = 4.08 μF,C2 = 6.19 μF and C3 = 3.30 μF. The switch is thrown ...
0
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0answers
20 views

Free body force diagram for offset clamp

Can someone please help me determine the free body force diagram for this offset clamp. I understand there should be a compression and tension force somewhere. I think the screw on the right exerts ...
1
vote
2answers
46 views

Would it be possible to make a space elevator only in the atmosphere?

I wonder if with current day technology we could make a "floating platform" which hangs from a satellite by a space elevator. This could allow a "launch process" involving floating a balloon to the ...
0
votes
1answer
36 views

How do you accelerate atoms/particles?

So I'm in 11th grade, and I'm writing a theory for my Physics professor and I need help. I need to know how you can make atoms/particles travel faster. For example, making sound travel a little bit ...
0
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2answers
49 views

Balancing a pencil

I came across this equation for balancing a pencil while solving some problems: $$ml\ddot { \theta } =mg\theta $$ Where $l=$the length of the pencil, and $\theta$ is the angle it makes with vertical. ...
1
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0answers
15 views

Homogeneous turbulence [on hold]

I'm trying to demonstrate the Karman-Howarth expression of isotropic turbulence for the velocity correlation functions: $R_{ij}(r)=A(r)_{ij} + B(r)\delta_{ij}$ since: \begin{align} A(r) r^2 + ...
0
votes
1answer
23 views

kinematics: parabolic movement [on hold]

How does the formula $ax^2$ is affected by the angle and the power of the launch of, let's say, a cannon ball, (regardless of its mass)? I am trying to create a simulation, and everything I have to ...
-2
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0answers
12 views

Calculating Power Ratio [on hold]

I have been given some practice problems. I have attached a table which I have to complete; for the first row (fundamental) I have calculated the dB value is -3 I have been given the formula ...
0
votes
1answer
10 views

Energy under constant pressure and temp

Conceptual problem: let A + 2B -> C + 2D be a reaction under constant pressure P and temp T, that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the molar enthalpy ...
-1
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0answers
17 views

Resistance in Potentiometer [on hold]

A potentiometer is shown in the figure. a) How will the balancing length be affected if resistance (R) is increased or decreased ? b) Will the balancing length be affected if resistance (S) is ...
1
vote
1answer
19 views

How do you show that the normal derivative of the magnetic vector potential is discontinous across a surface current?

This is from Griffith's "Introduction to Electrodynamics" 4th edition, problem 5.33. I need to show that $$ \tag 1 \frac{\partial \textbf{A}_{above}}{\partial n}-\frac{\partial ...
-4
votes
1answer
23 views

How I can solve this ? (kirchhoff's law) Plz discuss it to me [on hold]

the remaining of question is ( careful choice of suitable loop can make it easier ? i choose outer loop and answer it like that: 10 Volt = ( I X 10 ohm ) + ( I X 10 ohm) but it give wrong answer ...
0
votes
0answers
10 views

Transistor as Oscillator [migrated]

While I was studying the use of Transistor as an Oscillator from my Fundamentals Of Physics By Halliday, Resnick and Walker , I faced several confusions. My book says that when the switch S1 is ...
-1
votes
2answers
24 views

How do we prove that the initial velocity is equal to final velocity relative to centre of mass?

In elastic collision it is stated that the initial velocity relative to centre of mass is equivalent to final velocity of centre of mass of the same object. How do we prove that?
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2answers
48 views

With what initial speed does the person leave the ground to reach a height of 60 cm? [on hold]

An average person can reach a maximum height of about 60 cm when jumping straight up from a crouched position. During the jump itself, the person's body from the knees up typically rises a distance of ...
0
votes
1answer
20 views

Probability density function of a particle for computation

I'm writing a program, part of which relies on a particle being able to change location similar to a how a real particle would behave (pardon my physics). For example, on a grid of 100x100, a ...
-5
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0answers
45 views

Ok ok this is a homework problem, but I'm having trouble with it [on hold]

Where do I even start. I've converted the miles that I should be getting in total and arrived at 700 miles total. From here, any hints on what I have to do?
0
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1answer
45 views

Question about angular momentum operator

To show that the eigenvalue to $L^2$ is proportional to $\hbar^2$ is shown from $L_z=xP_y-yP_x$ $p_y=-i\hbar\frac{\partial}{\partial y}$ $p_x=-i\hbar\frac{\partial}{\partial x}$ ...
3
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0answers
44 views

How much work can a single grain of rice do? [on hold]

I found a website saying a grain of rice contains 1/10 kcal. I'm not a physicist and haven't done maths for a long time. But here's what I came up with: E = m * g * h One small calorie equals ...
3
votes
1answer
40 views

The ADM Energy of Gravitational Waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of Gravitational Waves.And they said the result ...
-1
votes
0answers
48 views

Why do motors have a speed limit? [duplicate]

The force which will move a body with this motor will be the difference between the force of the motor say 2N and the resistance - friction force - say 1N then the sum of forces will always be ...
-3
votes
0answers
25 views

Rocket needs to make course correction what mass of gass must be expelled [on hold]

A(n) 5200 kg rocket traveling at 3900 m/s is moving freely through space on a journey to the moon. The ground controllers find that the rocket has drifted off course and that it must change direction ...
-1
votes
0answers
13 views

How can I calculate wavelength in the following problem? [on hold]

Ultrasonic sound of frequency 100 KHz emitted by a bat is incident on a water surface. What is the wave length of reflected and transmitted sound? (Given that speed of sound in air is 340 m/s and in ...
-1
votes
0answers
37 views

Capacitor question [on hold]

Assume a 1200F ultracapacitor is initially charged to 12V by a battery and is then disconnected from the battery. If charge is then drawn off the plates of this capacitor at a rate of 1.0mC/s, how ...
2
votes
3answers
68 views

How can Denver offer Hot Air Balloon rides?

So the air density in Denver is 1.0 kg/m^3. And heated air has the density of 0.95 kg/m^3. So adding the weight of the basket and balloon I don't understand how a hot air balloon could get off the ...
1
vote
2answers
32 views

Working out velocity (including air resistance) [duplicate]

For my computing project, I am creating a projectile simulator but I cant seem to get my head round the air resistance. I tried by working out the horizontal and vertical velocity by solving it ...
0
votes
0answers
22 views

How to calculate explicitly the *external leg correction* diagram

I tried to calculate the Amplitude of the external leg correction of figure 6.1 in Peskin&Schroeder. I focus on the diagram with one incomming charged fermion $f^-$ (with momentum $p'$), then a ...
0
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0answers
55 views

What does basis function actually mean?

I want to know that how any signal can be represented as sum of basis vector and what basis function actually means? Can anybody explain with simple examples?
0
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2answers
48 views

How does the object at constant speed pass the accelerating object?

A car starts from rest and move with constant acceleration of $4\frac{m}{s^2}$ and at the same time a motorcyclist moving with a constant speed of $36\frac{km}{hr}$ overtakes and passes the car. ...
0
votes
0answers
33 views

Thermodynamics - Efficiency of an engine [on hold]

I am taking a mathematical physics course and got stuck on this rather simple problem Consider a thermodynamic cycle of monoatomic gas () I want to calculate efficiency of this cycle I know that ...
-4
votes
0answers
26 views

assume that air resistance is proportional to speed [on hold]

Assume that air resistance is proportional to speed. A particle is thrown directly downwards with initial speed equal twice it's terminal velocity. Obtain a fomula for the time it takes for its speed ...
0
votes
1answer
25 views

Derivation for certain non uniformly accelerated movements [on hold]

A sphere of $m_1$ is thrown at a speed of $v_i$ perpendicular to the surface from the surface into the atmosphere.. Are there equations for position $x(t)$ and the speed $ v(t) $ of the sphere at a ...
0
votes
2answers
25 views

If the force of friction is 20 N for a moving body does acceleration increase with the increase of the mass?

A body is moving and the only force acting on it is the force of friction. If we put another body on this moving body somehow the force of friction will increase; does its acceleration change?
0
votes
1answer
55 views

Light reflecting inside a sphere [on hold]

I'm having a bit of trouble cracking this problem. The diagram is given below. My job is to find $\phi$ as a function of $\theta$ and the index of refraction $n$. For this part of the question, I ...
0
votes
1answer
60 views

I need help with divergence and gradient? [on hold]

$$A_z = \mu{\frac{e^{-jBr}}{4\pi r}}∫I(z')e^{jBz'\cos\theta}dz'$$ Midway into my question, I want to compute: $$-j\left( \frac{\nabla(\nabla\cdot A) }{w\mu\varepsilon} \right).$$ Symbols like $ w, ...
0
votes
1answer
25 views

What are the support reactions at these points? [on hold]

How do I find the horizontal and vertical support reactions at A and C? I've tried balancing the moments and the forces in the x and y directions, and I can't seem to get it. Every time I try, I ...
0
votes
0answers
11 views

Statics- Ball and Joint Analysis [on hold]

I'm having trouble dealing with this problem. I know as much that there are reaction forces at point and tension forces in the direction of the cables, but I don't know how to obtain these forces ...
30
votes
6answers
4k views

Freefall into snow

In the movie Frozen, the following dialogue takes place: Anna: "It's a hundred-foot drop." Kristoff: "It's two hundred." Anna: "Okay, what if we fall?" Kristoff: "There's 20 feet of ...
-2
votes
0answers
26 views

Electricity. I'm finding difficulty answering this question [on hold]

Consider 3 identcal spheres, A,B,C. A carries a +5q charge. B carries a -q charge. C carries no net charge. Spheres A and B are touches together and then seperated. Sphere C is then touched to Sphere ...
0
votes
0answers
26 views

Mass-velocity-relation for tachyon

Suppose that $m = \gamma m_0$ with $$\gamma = \left(1-\frac{u^2}{c^2}\right)^{-\frac{1}{2}}$$ is valid for tachyons, where $m$ is the mass of the tachyon and $u$ its velocity. Since $u>c$, the rest ...
1
vote
1answer
29 views

Neutrino Reaction: Is the Following Reaction Allowed?

Is the following reaction allowed and why? $$ \nu_e \to e^- + \mu^+ + \nu_{\mu} $$ I would say it is allowed since individual lepton number and charge are conserved.
1
vote
3answers
44 views

How to find stopping distance of a car? [on hold]

I am trying to calculate minimum stopping distance of a car once the brakes are applied. I know the velocity at braking instant, i also know the distance from the obstacle. I found out that $$ d = ...
1
vote
1answer
34 views

Optics problem: Determining the new focal length when changing from film to CCD detector [on hold]

An older camera has a lens with a focal length of 50mm and uses 34-mm-wide film to record its images. Using this camera, a photographer takes a picture of the Golden Gate Bridge that completely ...
0
votes
0answers
63 views

In every glass of water there are water molecules that came through Hitler's urinary bladder? [on hold]

I was told that in every glass of water there are water molecules that came through Hitler's urinary bladder. How much it is true probabilistically?
2
votes
1answer
69 views

Why is it difficult to cook food on mountains?

Why is it difficult to cook food on mountains? Is it because on increasing pressure boiling point of substance increase and on mountains there is less pressure so less boiling point. Then shouldn't ...