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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-3
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0answers
13 views

Power system problem, can you please check if my working is correct?

Can you please check if my working out is correct, i have attached the photos of my working out.
0
votes
1answer
34 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
votes
1answer
30 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
votes
1answer
24 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
21 views

Finding time period of oscillations in a multiple spring system attached to a solid cylinder

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 figure. Find ...
0
votes
1answer
26 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
votes
0answers
22 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
vote
0answers
23 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
votes
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
votes
0answers
17 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 ...
0
votes
3answers
80 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.
1
vote
0answers
14 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 ...
-3
votes
0answers
10 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
votes
0answers
15 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
23 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
85 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 ...
-1
votes
0answers
27 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
36 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
36 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
votes
1answer
36 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
18 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
21 views

Turning ice into water in a calorimeter with steam?

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
27 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 ...
2
votes
0answers
28 views

Using the boltzmann equation to find neutrino decoupling temperature

I'm an undergraduate student currently following a particle astrophysics lecture. I was reading some stuff about the neutrinos decoupling before the $e^+ e^-$ annihilations. It's possible to quickly ...
0
votes
0answers
23 views

How do I get F1 force from this diagram? [on hold]

Hi, Can someone explain to me how to get F1 & angle theta? Much appreciated.
0
votes
0answers
22 views

Which is likely to experience a superelastic collision? (Multiple Choice) [on hold]

[Physics] So I think this question might be wrong, but I'm not sure, here it is: Q.Which is likely to experience a superelastic collision? a. A falling grenade b. A falling egg c. Two colliding ...
0
votes
0answers
16 views

Power radiated by a rotating annulus

I'm trying to solve a homework-kind of problem and I don't expect anyone to give me the solution. Rather, a little push in the right direction and tell me whether I made some mistake(s). Consider a ...
0
votes
0answers
47 views

Ejected Photoelectrons

A photon with of 13600eV energy interacts with a hydrogen atom at rest and ejects the electron (photoelectrically) in the direction in which the photon was travelling. If 13.6 eV is required to ...
0
votes
0answers
32 views

Brachistochrone parametric equations

I'm having a bit of a hard time understanding how the parametrized $y$ equation (given below) of the brachistochrone is correct. When these equations are plotted it gives a concave down graph. ...
0
votes
0answers
20 views

Motion in a plane - maximum velocity with which ball is projected from incline plane [on hold]

How to find the maximum velocity v with which the ball is projected from a incline plane A so that it returns back after hitting the plane B, e=1 for all collisions? Planes are vertical to each ...
0
votes
1answer
22 views

Neutron X collides with a stationary neutron Y when travelling directly towards it with velocity v. Show X will stop and Y will move off with v [on hold]

By writing equations showing conservation of kinetic energy and conservation of momentum, show that an elastic collision between neutron X travelling with velocity v directly towards neutron Y, which ...
0
votes
0answers
18 views

Finding the weight of wood in composite mass [on hold]

A 600N ship's anchor, which is made of steel, is fastened with a block of wood and the composite mass is immersed in fresh water. If one-fourth of the volume of the composite mass extends above the ...
0
votes
0answers
22 views

Pressure change with adiabatic compression problem [on hold]

So, I have to solve this problem: 2 moles of a perfect gas are compressed from $p_1=10$kPa to an unknown pressure, $p_2$. Throughout the process the temperature changes from $T_1=273.15K$ to ...
0
votes
0answers
22 views

Force of gravity exerted by/on Earth/Sun in a given coordinate system - not sure about the question [on hold]

I have a question: At a certain time in a coordinate system, the Sun is at the origin and the Earth is at position angle 225 degrees. What is the force of the Sun on the Earth? What is the force ...
0
votes
1answer
28 views

How to find Tension and force of contact [on hold]

A painter is applying force by himself to raise him and the box with an acceleration of 5 m/s2 by a massless rope and pulley arrangement.Mass of painter is 100 kg and that of box is 50 kg. If g = ...
0
votes
0answers
64 views

If I am in an elevator, with a weight of 120, and I am descending at 8 m/s, what is my apparent weight? [on hold]

Suppose your weight is 120 lb. You are riding in an elevator in the Sears Tower while standing on a bathrooms scale and watching readings. Imagine that the elevator keeps descending at a constant ...
0
votes
0answers
35 views

Forces on a block with a spring [on hold]

So I got this problem for HW but I dont think my results are okay: The 5 kg block rests on the surface with kinetic coefficient of friction 0.2. It is attached to a spring that is extended by 2 m. ...
0
votes
1answer
24 views

What is total force in this context?

One site said the total forces is the sum of the vectors. My homework question is "A skydiver of mass 90 kg is falling with a terminal speed of 60 ms-1. What does that mean? What is the total force ...
0
votes
0answers
17 views

Energy spring problem [on hold]

Online homework question. A 270 g block is dropped onto a relaxed vertical spring that has a spring constant of k = 2.0 N/cm. The block becomes attached to the spring and compresses the spring 12 cm ...
0
votes
1answer
42 views

Two masses on a frictionless surface connected with a spring

I have a problem with an assignment with two masses on a frictionless plane connected with a spring. Both masses are 1 kg, and the distance between them (the length of the spring) is 0.4 m. The ...
0
votes
0answers
33 views

Image formed by Refracting light

A jellyfish is floating in a water-filled aquarium 1.33 m behind a flat pane of glass 4.30 cm thick and having an index of refraction of 1.5. (The index of refraction of water is 1.33.) Where is ...
1
vote
0answers
32 views

Constant part of a photo taken [on hold]

(56th Polish Olympiad in Physics, II stage) A photographer has a camera with a lens of focal $f$ with can be set to a value from the interval $[f_{min}, f_{max}]$. The diameter of the diaphragm is ...
0
votes
1answer
22 views

Magnetic Field Along the Axis of the Current Ring - Alternative way to compute

This is Example 5.6 in Griffith's Introduction to Electrodynamics (4th Edition): Find the magnetic field a distance $z$ above the centre of a circular loop of radius $\ R$, which carries a steady ...
0
votes
1answer
29 views

What's my $dM$? Gravitational Potential inside a circle of mass

I'm trying to find the gravitational potential for an arbitrary point within a ring of uniform mass density. The point is constrained to be in the same plane as the ring. So we start with: ...
0
votes
0answers
20 views

Minimum Friction Coefficient-Lifting Of Rod [on hold]

What is the minimum coefficient of friction μ between a thin homogenous rod and a floor at which a person can slowly lift the rod from the floor without slipping to the vertical position applying a ...
0
votes
1answer
17 views

Constrained Motion of Connected Particles, Small Calculation Question

I am looking at this sample problem from Meriam Kraige - Engineering Mechanics Dynamics: When I do the differentiation, I end up with $\large -2\dot y+\frac{x}{\sqrt{x^2+h^2}}$ Where is the $\dot ...
-1
votes
1answer
39 views

A Textbook Problem From Rigid Body Dynamics(Cengage Bm Sharma) [on hold]

I was going through my textbook examples on rigid body motion. In this problem i can understand the derivation of equations 1,2 and 3,but can someone explain me the 4th equation?Please!!1
0
votes
1answer
34 views

How to find an equation for $x$ in terms of $t$ for a particle falling under gravity with resistance given by $mkv^2$? [on hold]

Okay so I have determine the velocity $v$ and displacement $x$ as functions of $t$ for a particle falling under gravity with resistance given by $mkv^2$. I have set up the equation of motion divided ...