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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5 views

Force on charged particle in magnetic field [on hold]

I am having difficulties achieving the answers to a question in my physics textbook. The question goes: A charged particle $q = 3.0 × 10^{–19}\space C$ and of mass $5.65 × 10^{–27} kg$ moves ...
-1
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0answers
19 views

Force and laws of motion, friction

The 12 kg block is put on the 3 kg platform which attached to the wire AB. The friction coefficient between 12 kg and 3 kg platform are ų(s)=0.6 and ų(k)=0.40. Determine the magnitude of acceleration ...
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0answers
27 views

Moment of inertia of cylinder

How to calculate moment of inertia of a cylinder about an axis passing through its geometrical center and inclined at an angle (\theta) with vertical.
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0answers
23 views

What will be the force on any point on a ring of Mass $M$ and Radius $R$ in space?

Me and my small brother were playing halo, he said wouldn't it be cool to live on a ring like that? I said that I highly doubt it will be possible as such a massive object in space will collapse to ...
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0answers
15 views

Gears in contact?

I was doing a practice exam paper question that was along the following lines: A gear, $A$,and moment of inertia $I_A$ is spinning about its axis at angular velocity $\omega$. Another gear $B$ ...
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1answer
15 views

Finding the acceleration of a mass/pulley system without knowing the direction of the displacement

I have the following question: I noticed that if I solve for the acceleration assuming that the acceleration is occuring to the left, I get the equation: $\displaystyle a = ...
1
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0answers
17 views

A level 9702/11/o/n/14 question 26 (about interference of sound wave) [on hold]

The speakers are identical and they are connected it's series with power, so I thought there would be complete destructive interference. Therefore, at some point the amplitude would be zero and also ...
2
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1answer
30 views

Finding final velocity in inelastic collision

Information: In a shipping company distribution center, an open cart of mass 49.0-kg is rolling to the left at a speed of 5.40-m/s (see the figure). You can ...
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1answer
19 views

Mass-Spring system on an accelerating jet

Imagine a perfect mass spring system. If it's put on an accelerating plane, how will the motion change? Is the plane's acceleration like a driving/damping force, where: $$F_{\text{driving}} = ...
2
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0answers
27 views

Calculating imaginary part of a loop diagram using cutting rules for phi^4 theory

I'm trying to calculate the imaginary part of this diagram in $\phi^4$ theory, using the optical theorem, and I'm having trouble. The cutting rules seem to suggest that this diagram is equal to ...
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0answers
34 views

Need help understanding $\oint H \cdot dl = I_{f,enc}$. Homework question [on hold]

A cylinder of radius R and magnetization $M = kr^2 \hat{\phi}$. I already found the magnetic field due to bound charges to be, $B = \mu_0 k r^2 \hat{\phi}$ inside the cylinder and $B = 0$ outside ...
2
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1answer
35 views

Variable Gear System

I have a variable speed gear system with 4 primary parts. I need to find the relationship between input rotational speed (wi) to output rotational speed (wo). Fig. 1 shows three of the primary ...
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0answers
34 views

Fermion commutation relations QFT question

Consider left-handed fermions in two spacetime dimensions $(t,x)$: $\psi_L=\frac{1}{2}(1-\gamma_5)\psi_D$ with $J_0^\epsilon(t,x)=\psi_L^+(x+\epsilon)\psi_L(x-\epsilon)$. (a). Use canonical ...
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1answer
18 views

Field inside an endless cylinder, without using Gauss's law

I need to prove that a field inside an infinitely long hollow cylinder, with density $\sigma$, is zero - without Gauss's law. I am clueless on what to do, how to start. Any clues, hints, guidelines? ...
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1answer
25 views

Potential Energy in modified Atwood Machine

The initial length of the spring is $l_0$. I need help understanding how the potential energy of this system comes to be. I know the answer: $$ U = ...
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2answers
56 views

What should we do If we wanted to increase the angular velocity of a planet? [duplicate]

We could hit it with really fast objects, but could we manipulate the orbit of a large satellite to speed up its rotation? What would be the easiest way?
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0answers
21 views

How to find the nature of an orbit knowing 2 altitudes and the time interval? [on hold]

A body was observed at an altitude of $366 km$ and then at $633 km$, after $12.5$ minutes. Angular separation between the 2 measurements is 45 degrees: find nature of orbit and true anomalies at 2 ...
1
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0answers
33 views

Super-luminal separation

Suppose there are are 5 bodies separating in space (due to it's expansion), and let us consider that they can emit light. 1st body moves in the -x direction, at the speed of light. 2nd body moves ...
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0answers
18 views

Physics question on heat produced in resistance ckt [on hold]

The charge $Q$ flowing through a resistance $R$ varies with time $t$ as $Q=at-bt^2$. The total heat produced in $R$ is: 1.a3R/b 2.a3R/2b 3.a3R/3b 4.a3R/6b
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0answers
22 views

Wave equations for reflected waves in standing wave calculations, when the end is fixed and when it is free?

Consider a sinusoidal wave moving in the +x direction $$y_{1}(x,t)=A\sin\left [ \frac{2\pi }{T} \left ( t-\frac{x}{v} \right )\right ]$$ (A) At a fixed end, the amplitude of the resultant wave ...
1
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1answer
34 views

Can Tension between two blocks on a horizontal plane be discovered in these conditions? [on hold]

the bodies are linked by an ideal string, one has m1=10kg & the other m2=20kg The force is known and is pulling horizontally, F=60N on the lighter object the coefficient of friction is said to be the ...
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0answers
21 views

Applying force to Keep constant velocity [on hold]

An object with mass 1kg is moving on an even plane. The plane has kinetic friction coefficient of 0.5. Gravity is pulling the ...
2
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3answers
51 views

movement of particles in electric field

I am confused about a homework problem. Let's assume we have two electrically charged particles of which we know the charge and mass respectively. Let's say that at first they are fixed at some ...
0
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0answers
15 views

Problem involving a rigid body in equilibrium [on hold]

A uniform rod rests in equilibrium with one end against a smooth vertical wall and the other against a smooth plane inclined at 30 degrees to the horizontal. Find the inclination of the rod to the ...
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0answers
22 views

Power system problem, can you please check if my working is correct? [on hold]

Can you please check if my working out is correct, i have attached the photos of my working out.
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1answer
42 views

Acceleration of Rain drop

Under the heading 'Points to remember',my textbook states: It is possible that an object can be increasing in speed when its acceleration is decreasing as in case of a raindrop. I could not get ...
2
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1answer
36 views

Gradient and curl of a field in polar coordinates

How do we determine the gradient and curl of a scalar/vector field in polar coordinates? For instance, if we have the following potential energy function for a force, $$U = ...
0
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1answer
32 views

Feynman Diagram in QED non relativistic limit

I am following Peskin to read Feynman diagram. But in this image given, he used the non-relativistic limit to write the incoming fermion gamma mu product. How did he get it? Any explanations in ...
0
votes
1answer
29 views

Finding time period of oscillations in a multiple spring system attached to a solid cylinder [on hold]

A solid cylinder of mass $m$ and radius $R$ is kept in equilibrium on horizontal rough surface. Three unstretched springs of spring constant $k$, $2k$, $3k$ are attached to cylinder as shown in the ...
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2answers
48 views

How to derive (the dimensionless coefficient in front of) the moment of inertia for common shapes?

Is there a way to derive (the dimensionless coefficient in front of) the moment of inertia for common shapes? I assume it has to do with the density of the shape, but I'm having trouble seeing it. ...
0
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1answer
28 views

Determining the velocity function for a particle on a rough inclined plane

This is a problem from the problem book by IE Irodov (Problem 1.106). We have a rough inclined plane with coefficient of friction $\mu = \tan\alpha$. A particle is kept on the incline and projected ...
0
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0answers
14 views

What is the Index of Refraction of the Liquid Varied with wavelength listed in the question [on hold]

A point source of light sits 0.5m below the surface of a liquid. The source produces a mixture of equal intensity red and blue light. The index of refraction of this liquid varies with wavelength ...
0
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0answers
23 views

Physics speed-time graph of a lift [on hold]

Hi I need help with a physics question, the question reads: Look at the speed-time graph for part of the journey of a lift up a skyscraper The lift travels 30m before it reaches it's cruising ...
1
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0answers
26 views

Neumann Green's function inside semi-infinite conductor [on hold]

Consider a semi-infinite conductor with uniform conductivity $s$ occupying the space $z>0$. What is the Green's function with Dirichlet and Neumann boundary conditions inside the region $z>0$? ...
0
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0answers
21 views

Finding the Theoretical Acceleration [on hold]

what is the theoretical acceleration in the 19.0 meter sprint trial? Time = 3.25 seconds. Velocity = 5.8 m/s
0
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0answers
21 views

Need help with physics derivation regarding RF accelerating cavities

So, below I am having the worst and hardest time getting from the third to last line (delta1) to the last line after the first order approximation is done! Ive tried everything!!! Anyone can help ...
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4answers
118 views

Where do sound waves go after being heard?

I honestly can't come up with anything that makes sense, because obviously, energy cannot be created nor destroyed. I think the question is pretty self-explanatory, so there isn't much to say here.
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0answers
18 views

How to solve Kinematics: two objects meeting in the air

A water balloon is dropped from the top of a 200m high tower. An alert archer at the base of the tower sees the balloon being dropped, waits for 5s, then shoots an arrow at 40m/s straight up towards ...
-2
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0answers
11 views

Heat Engines and Thermal Pumps [on hold]

A steam engine is to have its thermal efficiency improved from 8.00% to 10.0% while continuing to produce 4500J of useful work each cycle. a) Does the ratio if the heat increase, remain the same, or ...
0
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0answers
24 views

In which direction along a GaN (wurtzite) crystal are only Ga atoms being observed?

So, if you have an electron microscope image of a GaN crystal, and that it shows only white dots which represent Ga atoms. No nitrogen atoms are seen in the image. Along which direction is this ...
0
votes
1answer
25 views

Period of small oscillations of rotational disk [on hold]

This is a question on a university physics exam paper, and it doesn't seem immediately intuitive how the problem works. The answer is given, but not any details of the working. Also, I'm not sure if ...
1
vote
4answers
86 views

Gravitational force of a ring [on hold]

Given a ring with mass $m_1$, radius $R$ and a point mass $m_2$ with distance $x$ regarding the center of the ring. How can I calculate the gravitational force of this ring ? At first glance I'd say ...
0
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0answers
28 views

Derivation of Maxwell's equations [on hold]

I derived the equations of Maxwell in a current free medium, last year about this time (I need help editing this). I made use of complex quantities, and Cauchy-Riemann relations. In this derivation ...
-1
votes
0answers
14 views

How much is the gain of this Op Amp? [migrated]

I have a circuit like this. I want to calculate the gain of this circuit. If there is no R4 then it is easy to calculate.But now I have a problem. If I have a input current I=0.5A, then what is the ...
1
vote
1answer
37 views

How to calculate the Hamiltonian from the Lagrangian for a non-relativistic charged point particle in an EM field?

I was given the equation of the Lagrangian: \begin{equation} L~=~\frac{1}{2}m \dot{x}^2+\frac{e}{c}\vec{\dot{x}}\cdot \vec{A}(\vec{x},t)-e\phi (\vec{x},t). \end{equation} I proceeded to use the ...
1
vote
1answer
38 views

Work done in raising a rope at constant kinetic energy?

Usually the question I had was work done in raising a rope at constant speed. Obviously as you raise the rope, the mass changes over time. It'll be a simple integral. But what about work done in ...
0
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1answer
38 views

Lagrange equation and a force derivable from a generalized potential

I was reading the solution of this exercise and I have a doubt: A point particle moves in space under the influence of a force derivable from a generalized potential of the form $$U(r,v) = ...
0
votes
1answer
21 views

Explaining induced emf: directions of lorentz force and electrostatic field in two reference frames

First question, what is the direction of electrostatic field? Here is the problem: Consider a conductor rod CD moving at a speed v in a magnetic field. The three are in right angles to each other. In ...
0
votes
1answer
23 views

Turning ice into water in a calorimeter with steam? [on hold]

So there's this question I've been having trouble with here it is: A 0.050-kg copper calorimeter contains 0.050-kg of ice at -10°C. What mass of steam at 100.0°C is required to convert the ice to ...
1
vote
2answers
28 views

What makes a collision superelastic?

I've seen an online definition: A collision in which potential energy is converted into kinetic energy so that the total kinetic energy of the colliding objects is greater after the collision than ...