Tagged Questions

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.

learn more… | top users | synonyms (3)

0
votes
0answers
3 views

Force between two blocks on a friction less surface

The question is, A single horizontal force F is applied to a block of mass M1 which is in contact with another block of mass M2 as shown in the figure. The surfaces are ...
0
votes
0answers
8 views

Determine path of point mass using the Hamilton's principle

I am very new in this field but I try to solve a problem by using the Hamilton's principle and afterwards I want to compare the solution by solving the same problem using conservation laws. What I ...
0
votes
0answers
5 views

Finding the maximum extension of a Spring

I have solved that after the body m1 hits m2, the velocity of m2 is going to be (3/4)*v0. I did this by using the law of conservation of momentum and using the coefficient of restitution (relative ...
0
votes
1answer
9 views

How do I compute the angle needed to have a turning radius of $<8m$ and its wheel base with 20'' tire

I was doing a project of a vehicle, I'm assigend to the steering. I need to have a turning radius of $<8m$ however I'm limiting my space for the wheels. I've read that $>$ wheel base $=$ $>$ ...
0
votes
1answer
13 views

Tension after cutting the rope

In the image below how many times the tension in OA would change if i cut the rope where the scissor is?
0
votes
0answers
14 views

Calculation of the Poisson bracket of a (Classical) Yang-Mills generator

This question might be too technical or minute, but I believe someone can give me the right advise. What I want to calculate is a Poisson bracket algebra of classical YM gauge generators, ...
0
votes
0answers
8 views

How to correctly resolve forces radially in vertical circular motion?

I have always had problems at resolving forces and relating to Centripetal Force. Il show an example that I am stuck at right now. Please help me understand. This is the diagram: This is the ...
-1
votes
0answers
17 views

Could you explain me how 'I*dl x r' from Biot-Savart Law works for finite long wire?

http://cnx.org/contents/416f27b6-e016-47c5-b1f1-01f470fd2907@10/Magnetic_field_due_to_current_ I am studying this problem right now but can't move forward. Biot Savart law shows that ...
2
votes
1answer
17 views

Gibbons-Hawking-York (GHY) boundary term for Schwarzschild metric

What is the simplest way to calculate Gibbons-Hawking-York boundary term for Schwarzschild metric? \begin{align} \int ...
1
vote
1answer
40 views

Unitary change of X Basis: Shankar Exercise 7.4.9

I'm currently working through Shankar's Quantum Mechanics and am stuck on one of his exercises. In Exercise 7.4.9 Shankar would like us to show that: if $\mid x \rangle$ is changed to $\mid ...
1
vote
1answer
9 views

Find quantity of electricity of two circular faces

So, there are two circular conductive sheets with quantities of electricity of Q and -Q. If I know that the distance d between them is 0.002 meters and their radius is 0.1m and the voltage between ...
0
votes
0answers
24 views

protons and electrons can have different charges? [on hold]

I'm studying physics (self-learning) and I'm a bit confused with Columbs law. q1 and q2 are just particles (electrons or protons). 1 proton has a charge of 1.602 * 10^-19 C 1 electron has a ...
0
votes
1answer
23 views

Question regarding calculating acceleration due to gravity on planet Mercury [on hold]

I was asked to calculate the acceleration due to gravity on planet Mercury, if the mas of Mercury is $2,99 \times 10^{22} kg $ and its radius is $2,42 \times 10^{3} \ km$. The mass of the object is ...
1
vote
0answers
11 views

Finding final velocity of neutron [on hold]

A neutron moves with velocity $u$. It collides head-on with a stationary nitrogen nucleus. The collision is elastic. The mass of a nitrogen nucleus is 14 times that of a neutron. After collision ...
1
vote
1answer
13 views

A massive slider starts from rest from a point S (which is at the same height as a point T at the top of the track) [on hold]

This is a question from previous physics aptitude test. A massive slider starts from rest from a point S (which is at the same height as a point T at the top of the track) and slides along a ...
1
vote
2answers
33 views

Problem in understanding Newtonian 2nd law

In Resnick, Halliday, Walker s' Principle of Physics , I found this question : Two forces are acting on a block on a frictionless floor. On the left of the block $3~\text{N}$ & on the right of ...
6
votes
1answer
58 views

How to use Euler-Lagrange when Lagrangian is $L=\sqrt{t}\sqrt{1+(dy/dt)^2}$

In this Lagrangian problem, action is $$S = \int_{t_1}^{t_2} \sqrt{t}\sqrt{1+\dot{y}^2} \,\,dt$$ where $\dot{y} = dy/dt$ and $t_1$ and $t_2$ are some fixed points. I tried to solve this problem using ...
0
votes
1answer
28 views

Covariant derivative tensor [on hold]

Given that $T^{αβ}{_γ}^δ{_σ}$ is a tensor, I worked the covariant derivative as: $T^{αβ}{_γ}^δ{_σ} + Γ^{α}{_{ρσ}}T^{ρβ}{_γ}^δ + Γ^{β}{_{ρσ}}T^{αρ}{_γ}^δ - Γ^{ρ}{_{γσ}}T^{αβ}{_ρ}^δ + ...
0
votes
0answers
25 views

Screening in semiconductor

how can we get the following solution for the screened potential of a point charge Q: by using the following Thomas-Fermi equation as: where:
0
votes
1answer
41 views

Get angle to hit (x,y) with vertex [on hold]

In a projectile trajectory, I'm using the following equation to get the angle required to hit a target in x,y coordinates: This works great, however, it implies that the target is reached by one of ...
0
votes
2answers
33 views

Using the force law to obtain total energy of an electron as a function of its radius

I am working on a problem which starts saying determine the total energy of a hydrogen atom with an electron moving with momentum $p$ at a radius $r$. For that part I got: $E = \frac{p^2}{2m_e} - ...
0
votes
0answers
26 views

Boundary problem with forced vibration [on hold]

Consider the forced vibration of a string governed by $$\frac{\partial^2 u}{\partial t^2} = \frac{\partial^2 u}{\partial x^2} + Q(x,t) $$ subject to the boundary conditions $$u(0,t) = A(t)$$ $$ ...
2
votes
1answer
19 views

Are muon energies quantized?

I'm working on a problem that asks: For a central charge $Ze$, obtain an expression for the radius $r_n$ of the $n$th muonic orbit. Express this as a multiple of the radius $a_o$ of the first Bohr ...
0
votes
1answer
34 views

Force on ball going around loop [on hold]

Suppose I have a ball of mass m going around a loop. It is radius $r$, and rolling without slipping. Half way up the loop, what is the force in the $x$ an $y$ direction if it is at velocity $V$? I ...
2
votes
1answer
56 views

Representations of Galilei group

Show that the operator $U(\alpha, \beta) = e^{i(\alpha \hat{x}^2 + \beta \hat{p}_{x}^2)}$ can represent the space reflection of the 1D Galilei group: $x \to -x; t \to t$. I don't really know ...
0
votes
1answer
28 views

Parallel Resistors (special cases formula)

1) A car's rear window defroster uses $n=15$ strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged ...
3
votes
1answer
61 views

Bosonic Schrödinger field [on hold]

When second quantizating the Schrödinger field $$\psi(r,t) = \sum_i \phi_i(r)b_i(t),\quad\mbox{and}\quad \psi^{\dagger}(r,t) = \sum_i \phi_{i}(r)^* b_i^{\dagger}(t),$$ we have the commutation ...
1
vote
1answer
29 views

Work energy and laws of motion and friction problem?

I am having a confusion in the following question- Q-To stimulate car accidents auto manufacturers study the collision of moving cars with mounted springs of different spring constants. consider a ...
0
votes
2answers
47 views

What is a CCD structure?

In a exam paper for entry into Oxford University for physics, I came accross something which I hadn't met before, and I have no idea what the question is asking - none of my teachers could explain it ...
-1
votes
1answer
33 views

Question on kinetic energy, mass and velocity [on hold]

Two bodies have kinetic energies in the ratio of 4:1 They are moving with equal linear momentum. What is the ratio of their masses. My answer : I get $$\frac{m_1}{m_2}=\frac{4v^{2}_2}{v^{2}_1}$$
0
votes
1answer
27 views

Power - 1/2 Force x velocity? [on hold]

A pump, taking water from a large reservoir, is used to spray a jet of water with speed 20m/s. The nozzle of the pipe has radius 0.05m, and is level with the surface of the reservoir (no change in ...
-2
votes
0answers
23 views

laplace equation [on hold]

Consider $u(x,y)$ satisfying Laplace’s equation inside a rectangle $R=\{0\leq x \leq L, 0\leq y\leq H\}$ subject to the boundary conditions $$\begin{array}{rclcccrcl} \frac{\partial u}{\partial ...
0
votes
1answer
50 views

Boundary value problem

Consider the boundary value problem \begin{align} \frac{du}{dt}&= \frac{d^2u}{dx^2} , \\ u(0,t)&=0 \\ u(L,t)&=0 \\ u(x,0)&=f(x) \end{align} I know how to solve it using ...
0
votes
2answers
54 views

Nondimensionalization of a simple system [on hold]

A damped spring mass system is modelled below: $$m\frac{d^2y}{dt^2}=F_s+F_d\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space t>0$$ ...
0
votes
0answers
23 views

Help with 4-velocity [on hold]

The 4-velocity $\overline{U}=(U^0,U^1,U^2,U^3)$ corresponds to the 3-velocity, $\underline{v}$, in the sense that $\overline{U}=\gamma(v)(1,\underline{v})$. Express (a) $U^0$ in terms of ...
0
votes
1answer
26 views

Vertical motion initial velocity given max height

I'm having a hard time finding a formula that calculates the initial vertical velocity for a projectile that should reach a certain height. I'm using this formula to calculate both vertical and ...
0
votes
0answers
5 views

Minimum deviation [on hold]

A ray of light experiences a minimum deviation when passed symmetrically through an equilateral triangular prism. Calculate the angle of incidence of the ray when the refractive index of the glass is ...
0
votes
0answers
19 views

Forces at each point for a simple truss [on hold]

I have a truss here: It is given that the forces at point 2 are horizontally and vertically. Positive values for lowercase f forces indicate tension, and negative ones indicate compression. I ...
1
vote
1answer
33 views

Work done in case of an accelerating object [on hold]

How do you calculate work when opposing force is less than applied force. So a 5 N static friction force is overcome by 15 N manual force for say 5 meter. What is the work done by manual force?
2
votes
3answers
66 views

Calculating vector to aim for moving asteroid (3D asteroid game)

Considering we're in a 3D system of coordinates: our ship is at point A, motionless our ship can shoot bullets, the speed of which is known the asteroid is at point B the asteroid is moving on known ...
-1
votes
0answers
22 views

Physics question dealing with friction and something else [on hold]

I have 2 questions A 10 kg block is placed on top of a 20 kg block. The top block is then pulled toward the right with a force of 60 n. IF the coefficient of f kinetic friction bewtween the floor ...
0
votes
1answer
79 views

Verifying a solution to Einstein's vacuum field equations

I need to verify a solution to Einsteins vacuum field equations. I have the solution as follows $$ds^2=a\,dt^2+b\,dr^2+\cdots$$ Is the following the right approach? Einsteins equation reduces to ...
-4
votes
0answers
40 views

What can be a differential solution for $\frac{dy}{dt}= -Cy$? [on hold]

which of the following can be a differential solution for $\frac{dy}{dt}= -Cy$ a) $y(t)=2cos(Ct)$ b) $y(t)=5e^{Ct}$ c) $y(t)=5sin(Ct) + 2cos(Ct)$ d) $y(t)=5e^{-Ct}$ e) $y(t)=4sin(Ct)$
0
votes
2answers
40 views

Slope With Varying Kinetic Friction [on hold]

I am stuck on the following problem; On a winter’s day in Maine, a warehouse worker is shoving boxes up a rough plank inclined at an angle α above the horizontal. The plank is partially covered ...
2
votes
5answers
178 views
+200

Is this expression for the kinetic energy of a spinning disk revolving about a second axis correct?

My question is motivated from a question from another user. You can see the configuration of the rotating system here: One disk/ring in double rotation and sum of energy. I am not interested in all ...
0
votes
0answers
15 views

General relativity, expressing a distance in terms of the metric tensor [on hold]

My starting point is: I've been told in the question. The interval between events which belong to the same world line of light equals zero, so I think that means ds = 0. So I now have: From ...
0
votes
3answers
39 views

Derviation of group velocity

I am working thru a derivation of the group velocity formula and I get to this stage: $$y=2A\cos(x\frac{\Delta K}{2} -t\frac{\Delta \omega}{2})\sin( \bar k x-\bar \omega t)$$ Then all the derivations ...
2
votes
2answers
28 views

Bungee jumping - find spring constant

A person of mass $m$ is attached to a spring that its loose length is $l_0$. He is standing on a bridge and jumps off it, so he travels down a distance $2 l_0$ when measured from the bridge up to the ...
0
votes
2answers
34 views

Since no current flows, the voltage is 0?

I didn't understand that , "Since no current flows in the ammeter the potentioal difference is 0 " How did they conclude that? I made this example So i made this example in paints , (R square ...
0
votes
0answers
15 views

Light angles measured in moving reference fame (SR, homework)

I've managed to get through all of this question without trouble until part d). The full question is given here: I've calculated the "true" angles of Star A and Star B as 71.57 degrees and 45 ...