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0answers
380 views

Numerical solution of two coupled second order differential equations of motion [closed]

Is there a numerical algorithm for solving a pair of coupled second order differential equations? This question arises from a homework problem that I have that involves two dimensional projectile ...
0
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2answers
59 views

Molecules of a solid [closed]

Question: Molecules of a solid : (a) are always in a state of motion (b) move only when heated (c) move because they are loosely bound (d) do not move at all My attempt: I ...
0
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1answer
76 views

Propulsion force [closed]

My physics instructor gave us a general problem A box is sitting motionless on a rough, horizontal patch of ground. You give it a good kick, so that it slides to the right with an initial speed of ...
0
votes
1answer
429 views

Determining $y$ coordinate of charged particle motion [closed]

I've tried several different ways, with a tutor, and with other colleagues. One of my colleagues has even gone to the professor with whom he worked out an equation for the component, and it was later ...
-1
votes
1answer
25 views

Computing power based on weighted averages [closed]

I'm struggling to understand the reason why I'm getting different results with two apparently similar ways to compute the power consumption (over multiple time intervals) of an electrical circuit. ...
0
votes
1answer
48 views

Help with momentum question involving vectors/trig [closed]

The problem: A car with a mass of 1200 kg and speed 10 m/s runs into a traffic barrier at an angle of 45 degrees, and is thrown outwards at an angle of 45 degrees relative to the barrier with a speed ...
0
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0answers
36 views

Force exerted by a capacitor on a polar object

I was reading about capacitors and wondered what the force an electrostatic field created by a capacitor would be on an object with a certain charge and mass. If it can exert a force on a polar object ...
-1
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1answer
42 views

Finding charge (electromagnetism course) [duplicate]

I'm a maths undergrad taking a course on electromagnetism, I've drawn a diagram to represent this following question, but I'm having a bit of trouble approaching it: "Two tiny balls of mass m = 0:1 g ...
0
votes
1answer
71 views

Power and speed [closed]

I'm asked to calculate how much POWER a 1210kg car needs to drive with a 85 km/s speed up a 655 meter long slope of 4.5°. I can find how much energy and work is required to do this, but isn't ...
1
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2answers
49 views

Final position of an object after aplying several horizontal forces [closed]

I'm given an object with a starting position. Several horizontal forces are applied to this object one after the other for different amounts of time. How can I determine the final position $x$?
4
votes
1answer
76 views

How to get a function for the voltage across a capacitor connected to an AC voltage source? [closed]

I am looking for the way of obtaining a solution for $V_{c}$ ,as a function of $t$ depending of $\omega$, of the following differential equation related to an electrical circuit involving a low-pass ...
1
vote
1answer
95 views

How to find the center of mass? [closed]

A massless rod of length $L$ attached to mass $m$ and with axle to cart of mass $M$. The cart has a shape of equilateral triangle (edge $L$). the cart is at rest and its center of mass is above $x=0$ ...
3
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0answers
76 views

Vertex for quartic interaction of complex scalar multiplet

Since I'm new to QFT and I tend to do a lot of errors during calculations, I would like you to tell me if I got the four-point vertex of the quartic interaction with a multiplet of complex scalar ...
1
vote
1answer
93 views

Moment of inertia of a system in different cases

A rod of mass $m$ and length $l$ is pivoted at one end to ceiling and free to rotate in the vertical plane. A disc of radius $R$, which is less than $l$, can be fixed at its other end in 2 ways : ...
0
votes
1answer
130 views

Wavefunction Problem wrong in solutions manual? [closed]

Well there is a problem in my book which lists this problem: Calculate the probability that a particle will be found at $0.49L$ and $0.51L$ in a box of length $L$ when it has (a) $n = 1$. Take the ...
0
votes
2answers
320 views

In Which of the following situations would force be exerted on on object and no work be done on the object?

Consider the following question: In which of the following situations would a force be exerted on an object and no work be done on the object? I. a centripetal force is exerted on a moving ...
0
votes
1answer
250 views

Help understanding a potential energy problem [closed]

Apologies if the following problem does not seem to involve potential energy, it is a homework problem that is labeled under the potential energy chapter. Question While a roofer is working on a ...
1
vote
1answer
77 views

Does the 1-D poisson's equation have monotonic potentials if $\rho=\rho(\phi(z))$?

I am solving the 1-D poisson equation: $$\frac{d^2 \phi}{dz^2}=-4\pi\rho(\phi)$$ with the additional requirement that $\rho(\phi(z=0))=0$. If I start by multiplying each side by $\frac{d\phi}{d z}$ ...
0
votes
2answers
214 views

How to choose a location for rocket launching?

What's the relation of earth's magnetic equator with satellite launching? How does the nearness of a rocket launching station to the earth's magnetic equator make it an ideal location for scientists ...
0
votes
0answers
22 views

Radiometric Intensity of Non-Monochromatic LED

So I have a problem with the LED with the spectrum shown below I am asked to find the radiometric intensity in Watts/steradian given that the LED produces $5.6\times 10^{-3}$ mcd. We are also told ...
0
votes
1answer
35 views

Equation of conservation of mass for isotropic fluid considering external forces [closed]

I have trouble doing the following problem: Consider a fluid isotropic in three dimensions such that one can ignore all dissipative forces effect, as would be the viscosity. By analyzing the flow ...
0
votes
1answer
99 views

Two masses attached by a spring [closed]

Suppose there is a system of two masses $M_1$ and $M_2$ connected by a spring with constant $K$ on a frictionless surface. What is the frequency of this system's oscillation? So I have fixed a ...
2
votes
2answers
252 views

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere?

What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere? the comet is falling radially towards the earth. Will this velocity be ...
0
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1answer
349 views

How to find power factor value of parallel RL circuit knowing the power factor value for the series circuit with the same components

Because I know the value for the power factor for the series RL circuit I've tried to find the ratio between the series circuit power factor and the parallel circuit power factor, expressed in terms ...
4
votes
2answers
108 views

Top angular speed of electric motor

I recently came across a question asking the following: If a motor is switched on, it quickly reaches a top speed. Why does it not just go faster and faster and faster? I thought it might be ...
0
votes
1answer
50 views

Finding acceleration using rotational dynamics [closed]

I'm asked to find the linear acceleration of this object for a given tension $T$ knowing that both discs have mass $M$ and we don't consider the mass of the bar. The answer of the book is ...
1
vote
1answer
93 views

How do I obtain the Lagrangian in standard for using action? [closed]

I have action as shown below $$S=\int \mathrm{d}t \int \mathrm{d}x^3 \bar\psi\left(i\partial_t\psi +\frac1{2m}\bar\nabla^2\psi-V(x)\psi\right)$$ How do I manipulate it to obtain the Lagrangian ...
0
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1answer
58 views

Finding the Lagrangian from the derivative of position

I have to find the Lagrangian for a system. In the point of interest I have come up with the following position coordinates: $$x = Rcos(\omega t)+\ell sin(\phi)$$ and $$y = Rsin(\omega t)-\ell ...
3
votes
1answer
96 views

Nonlinear Klein Gordon equation

For the Klein Gordon nonlinear equation, $$ u_{tt}- \Delta u +f(u)=0,$$ how could I use Noether's theorem to prove that there is a conserved quantity? I.e., $$ (\Pi _{k} )_{t} - \rm div(j_{k})=0 $$ ...
0
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0answers
42 views

Determining impact velocity over long distances [duplicate]

Everything I have found concerning impact velocity from a given height deals with constant acceleration due to gravity. I would like to know how to work in varying acceleration into the equation. So, ...
0
votes
2answers
135 views

Energy to move The Earth to mars' orbit?

How much energy would it take to add to the earth's orbital velocity to push the earth into mars' orbit? My thoughts: So, in 1-2 billion years, the sun will gradually get brighter. Suppose a future ...
2
votes
1answer
68 views

Translation Operator for Position on Momentum

Consider the translation operator $$\hat T=\exp[-ic\hat p/\hbar], $$ which acts on the position operator in the following way: $$\hat T^\dagger \hat q\hat T = \hat q+c.$$ If I take $\hat T ^\dagger ...
0
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0answers
55 views

quantization with a pure exponential potential

Given the Hamiltonian $$ H=p^{2}-ge^{-x}, $$ are the energies negative? If I impose the boundary condition $y(0)=0$ and $y(\infty)=0$, I get the condition for the energies $$ J_{2i \sqrt{E(n)}}(g) ...
0
votes
2answers
91 views

Electric field in two sphere system

Hi guys I'm really confused by this electric field question. Basically for the given setup shown, draw a graph of how electric field varies with distance from the center, given that radius of ...
2
votes
1answer
111 views

Three dimensional wave packets in momentum space

I am given the 3D wave packet: $$\psi(x,y,z)=N\,\exp\left(\frac{-(x^2+y^2+2z^2)}{2a^2}\right).$$ I was asked to find N (easy enough). Then I was asked the probability that we measure $z$ greater than ...
4
votes
2answers
419 views

Angular momentum in a rod rotating around one end?

Sorry if I can't get straight to the point, I have to give a lot of details before I actually state the question. The formula for angular momentum is $L=I \omega$. If we look up $I$ for a thin rod ...
3
votes
0answers
55 views

Property of stress-tensor in flat spaces

Let $T_{ab}$ be a stress-tensor in a flat space satisfying conservation equations. Define $$ P^i=\int T^{oi}d^3x, \;\; D^i=\int T^{00}x^id^3x $$ Can anyone show me how to prove $$ \frac{dD^i}{dt}=P^i ...
1
vote
1answer
131 views

Apparent depth and the viewing angle [closed]

Does the viewing angle of a person observing a coin placed in a bucket of water affect the apparent depth in any way?
2
votes
2answers
1k views

Relationship between stopping potential and work function

Suppose I have a cathode with a work function of 3eV and an anode at a potential of 2V above the cathode. If a photon having 2eV of energy hits the cathode, what happens? A. An electron is emitted ...
0
votes
2answers
203 views

Electrostatics kinematics equations (Coulombs Law)

If there are two similarly charged particles $Q$ and $q$ of masses $M$ and $m$, a Coulomb force is applied on each one (action-reaction). Suppose that $Q$ is stationary and we are shooting $q$ with an ...
0
votes
2answers
1k views

How to plot $(x,y)$ coordinate of projectile motion (with air-resistance)? [closed]

I am trying to plot a graph to show the difference in projectile motion when it has air-resistance and when it doesn't have air-resistance. I set the mass, $v_0$ and $\theta$ as constant I can plot ...
2
votes
0answers
90 views

Momentum representation of a state

I am trying to figure out the momentum representation of the state which has the properties $$\langle \psi |\hat q |\psi \rangle=-q_0,$$ $$\langle\psi|\hat p|\psi \rangle=p_0, $$$$\Delta q\Delta ...
2
votes
0answers
58 views

Translation Operator on two operators

On my last HW set, we were asked to show that the operator $$\hat T = \exp(-ic\hat p /\hbar)$$ acts as a translation operator ($\hat T^\dagger q\hat T=q+c)$. This was simple to show using commutators ...
2
votes
0answers
98 views

Pauli matrices product identity

How to prove the identity $$ \tilde {\sigma}_{\alpha}\sigma_{\beta}\tilde {\sigma}_{\gamma} = g_{\alpha \beta}\tilde {\sigma}_{\gamma} + g_{\alpha \gamma}\tilde {\sigma}_{\beta} - g_{\beta \gamma} ...
0
votes
2answers
138 views

Ideal gas law problems

I got really confused about real gases volume and ideal gas volume. Ideal gas molecules take up no space, if we put gas into a 2.4L water bottle, we know that all the gas will expand all over the ...
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votes
1answer
311 views

Given moment about a pin and a roller [closed]

sorry to ask, have not been a able to find a similar question to mine. For this problem, given moment $M_2$, distances $a$ and $b$ My reasoning is that we have two support reactions and points A and ...
3
votes
2answers
129 views

Pressure versus Volume system problem

A rigid air tight container of volume 1.5 m$^3$ is filled with a gas of density 8 kg/m$^3$. The container has a density meter that allows us to watch the changes in density in the gas in the ...
0
votes
0answers
59 views

Spectroscopy: clarification about doppler shift

I've just begun to study spectroscopy, and I need a clarification about the Doppler Effect. Considering this graph: could you explain me how I can see the doppler shift related to the deeper peak ...
0
votes
2answers
74 views

Entropy of a chain

A chain has N segments which can be oriented in either the x or y directions. For each segment oriented along y, there is an energy penalty of $\epsilon$. We also know the end segment is at $(L_x, ...
1
vote
1answer
349 views

Commutator of parity and Hamiltonian operators under even potential function

I need to show what is $[H,P]$ where $H$ is the Hamiltonian and $P$ the parity operator. $V(\underset{\sim}x) = V(-\underset{\sim}x)$ in this case. I start off with $$ \langle ...