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 views

Heat Engines and Thermal Pumps

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
4 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 ...
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1answer
21 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
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4answers
77 views

Gravitational force of a ring

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 ...
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0answers
25 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 ...
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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
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1answer
34 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 ...
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1answer
33 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 ...
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1answer
34 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
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1answer
17 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 ...
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1answer
13 views

Turning ice into water in a calorimeter with steam?

So there's this question I've been having trouble with here it is: (Question is in Bold) 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 ...
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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
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0answers
27 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 ...
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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.
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0answers
21 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 ...
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0answers
14 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
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0answers
46 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
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0answers
31 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
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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
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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
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0answers
17 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
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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
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0answers
21 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
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1answer
25 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
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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
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0answers
34 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
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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 ...
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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
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1answer
40 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
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0answers
30 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
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0answers
31 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
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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
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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: ...
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0answers
19 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
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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 ...
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votes
1answer
37 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
32 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 ...
0
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0answers
31 views

Maxwell Relations in Thermodynamics - Specific Heat [on hold]

I am not able to solve that question: Using Maxwell relations and the fact that $C_p = T \dfrac{\partial S}{\partial T}\Big|_p$ $C_V = T \dfrac{\partial S}{\partial T}\Big|_V$ Show that I can ...
3
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1answer
40 views

Operator Dimension and Field Transformation under Rescaling

In conformal field theory the operator dimension $\Delta$ determines how fields and thus correlation functions behave under rescaling. I am having trouble seeing how this number arises from a scale ...
0
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0answers
38 views

Linear diatomic lattice - Brillouin zone [on hold]

Consider a linear diatomic lattice. Show that the amplitude equations $$A[2 \mu - m \omega^2] = 2 \mu B \cos(ka/2)$$ and $$B[2 \mu - m \omega^2] = 2 \mu$ A\cos(ka/2)$$ at the Brillouin zone ...
0
votes
0answers
34 views

What will happen to this fan in this situation?

Lets say I have a pipe with a fan at the end of it and it is drawing ambient air from the other end of the pipe. Once I account for some blockages and looking at the fan curve, it was found the ...
1
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0answers
53 views

Gauge invariant quantities

In the context of cosmological perturbation one write the most general perturbed metric as $$ ...
0
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0answers
41 views

Electric Potential - Calculating Potential Difference [on hold]

An electron is to be accelerated from $3.0*10^6$ m/s to $8.0*10^6$ m/s. Through what potential difference must the electron pass to accomplish this? Use formula for potential difference: $dV = ...
0
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0answers
25 views

GCSE Force and Motion [on hold]

Four men use a snowmobile to travel across ice and snow. It has a mass of 288kg and the men are 78kg each on average. a) What force does the full snowmobile exert on the ice when it's standing ...
0
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3answers
60 views

How to find out how far a ball will travel after it's 3rd bounce?

Suppose I drop a ball from a height $H$ above a flat ground, how can I determine how far it will have traveled by the time the ball hits the ground for the 3rd time $L=x$?. I know how to calculate ...
0
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3answers
76 views

Why is the range of a projectile proportional to the square of the initial velocity?

I was watching the MIT lecture about projectile motion and the lecturer asked why $$D=\frac{(v_0)^2\sin(2\alpha)}{g}$$ Why is it $(V_0)^2$ not $V_0$? It is a hypothetical question i know that the ...
1
vote
2answers
90 views

Kepler's Laws to Determine Radius of Circular Orbit

"In nonrelativistic limit of general relativity there is a correction to the Newtonian gravitational potential energy $−h/r^3$ with $h = αL^2/(mc)^2$, where c is the speed of light, α = GMm and L is ...
0
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1answer
29 views

Starting point for a derivation of fictitious forces

I came across this expression at the start of a derivation of fictitious forces: $$(dA/dt)_L = (dA/dt)_R + \omega \times A$$ Where the $L$ subscript refers to the laboratory (inertial) reference ...
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0answers
22 views

Complete equations of motion in the scattering problem [on hold]

How to derive the complete equations of motion for an electron scattered by a proton using Lagrangian formalism?
0
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1answer
24 views

Magnetic field due to sheet current [on hold]

Suppose we have current flowing along very long thin sheet with current per unit length as $\lambda$ so what would would be magnetic field at distance $r$ from this sheet? Using Ampere Law ...