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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4 views

Amplitude of electric field produced by satellite dish

A telecommunications satellite is in geostationary orbit and it has a 1 m transmitting dish optimised for coverage of Europe. If the output power from this dish is 100 W, very roughly estimate the ...
0
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0answers
6 views

Calculating work needed to move a charge between plates of an uncharged capacitor

My first guess was zero work because there's no electric field(I think). E.g. a parallel-plate capacitor $4.9 cm$ on a side, spaced $1.0mm$. The work needed to move $6.8\mu C$ seems to be $1.1J$ And ...
-2
votes
2answers
31 views

Finding the initial velocity of projectile

What is the formula for calculating initial velocity of projectile using the conservation of energy given the mass, height, angle ?
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1answer
25 views

Are Q1 and Q2 attracted or repelled to the sphere shown in the figure below?

Can you tell from the image below if Q1 and Q2 are attracted or repelled. Will Q2 only be attracted to the sphere if Q2 is enough bigger than Q1? Will the positive charge inside the shell attract ...
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0answers
13 views

Find direction and magnitude of net electrostatic force on a point charge

Question: Find the direction and magnitude of the net electrostatic force exerted on the point charge $q_2$. Let $q = +2.4μC$ and $d = 33cm$. What I tried: I used the formula $F = kq_1q_2/d^2$ to ...
1
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2answers
68 views

Conservation of angular momentum - exercise

A sphere of mass $M$ is rotating with constant $w_0$ regarding the axis that intersects the north and south pole of the sphere. A bug of mass $m$ sits on the north pole and starts to walk along a ...
-3
votes
0answers
23 views

Resistors in series [on hold]

Let $P$ be the equivalent power of three resistors of powers $P1$, $P2$, and $P3$, and let $I$ be the current flowing through the circuit. We know that voltage is $V = v1 +v2 + v3$ and: $$V = PI\\ ...
-3
votes
1answer
26 views

Non zero accetion, varying speed

Can an object have non zero acceleration without having varying speed? How? Can you explain with an example please.?
-2
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0answers
20 views

Max speed of a turning disk for an object to stay at rest

A coin is at rest relative to a disk moving with a angular speed of w: The coin weighs 0.010 kg The distance of the coin to the center of the disk is of 0.20 m The static friction is of 0.45N ...
-1
votes
0answers
16 views

Finding the magnetic field [on hold]

A mechanical pendulum is made of a metal rod, one end of which is attached to a string. The mass of the rod is $m$ and the string length is $l$. The oscillation period of the thus obtained pendulum ...
0
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0answers
16 views

Initial current, RC Circuit

The task goes like this: The voltage between the points A and B, in the circuit diagram below, is 100 V. What's the initial current through the resistor when we close the switch S? (Other components - ...
-2
votes
0answers
20 views

Finding displacement of spring [on hold]

Q) A block lies on a horizontal frictionless surface, and the spring constant is $50\,\mathrm{N/m}$. Initially, the spring is at its relaxed length and the block is stationary at position $x=0$. ...
0
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0answers
21 views

The minimum force required to lift a triangular prism

If I have an isosceles triangular prism of mass m with the angle at the top being $2\theta$ I want to work out the minimum force I would need to apply to the upper faces to lift the prism. Lets say ...
0
votes
1answer
48 views

Solving the Three-body problem numerically

I want to create a program in $Mathematica$ that solves numerically the Three-body problem by Euler-Lagrange's equations. I was searching some methods to sucessfully do it. So I found a way to solve ...
-1
votes
1answer
9 views

Magnetic field size from electric field [on hold]

An electric charge oscillates about the origin along the y axis. A distant observer is located at a point on the +z axis. You observe the wave from a given location and find that at a given ...
0
votes
2answers
42 views

Derivation of $v=u+at$

I read the derivation of $v=u+at$ using integration. The steps are as follows - $$\frac{dv}{dt}=a dt$$ $$dv=adt$$ $$\int dv=\int a dt$$ $$\int dv=a\int dt$$ $$v=at+c$$ My questions are as follows - ...
1
vote
1answer
41 views

How much is time slowed down inside a planet or star?

An answer to What would be the rate of acceleration from gravity in a hollow sphere? states "that according to General Relativity time passes more slowly inside a hollow massive sphere than it does ...
0
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2answers
44 views

Potential difference inside charge distributions

Always when I think about potential difference inside a symmetrical charge distribution, I think of it being equal to zero because it's dependent on the field and I imagine the directions of each of ...
3
votes
2answers
99 views

Is Marshmallow solid or liquid?

A marshmallow is a sugar candy that, in its modern form, typically consists of sugar, whipped to a spongy consistency, molded into small cylindrical pieces, and coated with corn starch. Link ...
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votes
2answers
27 views

Electrostatics question cbse 2015 [on hold]

''The outward electric Flux due to charge +Q is independent of the shape and size of the surface which encloses it.'' Give two reasons to justify this statement.
0
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2answers
32 views

Question on heat

Is this statement correct? The oxygen and nitrogen molecules in a box has equal average kinetic energy but the oxygen molecules are faster. I am not sure because I thought oxygen molecules should move ...
-2
votes
0answers
12 views

Sliding ladder kinetic energy in generalised coordinates [on hold]

This is a problem from Hand and Finchs' Analytical Mechanics, in a chapter looking at holonomic constraints and generalised coordinates in Lagrangian Mechanics. A ladder of length $L$ and mass $M$ ...
-2
votes
0answers
43 views

Proof of definitions of scalar product [on hold]

I am looking a problem (no 1.7) from the first chapter of book classical mechanics by John Taylor. I have spent so much time but can't find solution how to relate the definition of scalar product. ...
0
votes
1answer
41 views

Two isobars they differ in binding energy, will they differ in radius as well?

It is a problem from introduction to nuclear physics- by krane, chapter: nuclear properties, problem 7. It goes like this: From the known masses of $_{~~8} ^{15}\rm O$ and $_{~~7}^{15}\rm N$, compute ...
0
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0answers
33 views

Find distance vs. time for a space ship moving through cloud of dust of uniform density [on hold]

Here's a problem: We have a cylindrical spaceship with cross-sectional area $A$ moves through a stationary cloud of dust of uniform density $\rho$. Initially the ship has some speed $v_0$ and some ...
0
votes
0answers
20 views

Magnetic field due to long current carrying conductor at a point near its end [duplicate]

How can one show that the magnetic field due to an infinite long current carrying conductor (length a) at a point near its end is given by $$B = \frac{\mu_0I}{4\pi a}$$ using Ampere's Circuital ...
1
vote
1answer
28 views

Time for two relativistic objects to meet

How do you prove that the time for two objects traveling towards each other at relativistic velocities is still d/(v1+v2). Answer seems to have something to do with velocity addition but I'm ...
-2
votes
0answers
20 views

3 point masses;circumference [duplicate]

3 gravitating mass points of mass m are on the circumference of a circle with the same distance r to each other. At $t=t_0$ one lets go of the mass points and each of them moves within the ...
-1
votes
1answer
39 views

Dirac field creation and annihilation operators [on hold]

i have to prove the following equations. Can someone give me a hint please?
0
votes
0answers
37 views

Changing the melting point of ice

Myself and a friend have been stuck on this problem for a while now. We know that we should end up with an answer of $-0.007K$ however, cannot get to this solution. Help with the method we should use ...
0
votes
1answer
50 views

Can't derive FRW Christoffel symbol

I'm trying to confirm that the $\Gamma^1_{01}$ Christoffel symbol of the FRW metric is $\dot{a}/a$. I have the FRW metric: $$ds^2=-dt^2+a(t)^2\left[\frac{dr^2}{1-kr^2}+r^2(d\theta^2+\sin^2\theta\ ...
0
votes
2answers
28 views

Yaw angle calculation for a two-wheeled inverted pendulum

[Sorry, if this is a basic question. I'm a software engineer, learning mechanical engineering concepts by trying to build a self-balancing robot] I'm unable to understand the yaw angle equation: ...
0
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0answers
15 views

Two charged rods placed along the x and y axis respectively [on hold]

Two charged rods of equal length $L$, $OA$ and $OB$, are placed along the $x$ and $y$ axis, respectively, $O$ being the origin. The rod $OA$ has a charge $+Q$ while the rod $OB$ has a charge $-4Q$. ...
0
votes
1answer
37 views

What does this problem about lenses really want? [on hold]

This is the problem: The distance between the lens of a simple remote camera (means it's not used to take pictures of close things) and the film is 40mm. how much should we move the lens to get ...
0
votes
1answer
23 views

A solid non-conducting sphere of radius $R$ carries a non uniform charge distribution [on hold]

A solid non-conducting sphere of radius $R$ carries a non uniform charge distribution with charge density $ ρ = k r/R$, where $k$ is a constant and $r$ is the distance from the center. Show ...
0
votes
3answers
25 views

A charge $Q$ is placed at a distance $a/2$ above the center of a horizontal square surface of edge $a$ [on hold]

A charge $Q$ is placed at $a$ distance $a/2$ above the center of a horizontal square surface of edge $a$, while a second charge $Q$ is placed below one of the vertices of square. Find the flux of ...
-3
votes
0answers
45 views

Mechanical energy? [on hold]

A particle of mass $2\,\mathrm{kg}$ is attached to one end of a model spring that is hanging vertically from a fixed point O. The spring has stiffness $4$ and natural length $1\,\mathrm{m}$. ...
1
vote
0answers
29 views

Potential (which only depends on the length of a position vector) [on hold]

a) A potential $U$ only depends on the length $r=|\vec{r}|$ of the position vector $r$. Show that $$\vec{\nabla}U(r)=U'(r)\frac{\vec{r}}{r}. $$ What properties does this vector field have? ...
-2
votes
0answers
52 views

Gravitating masses on a circumference [on hold]

3 gravitating mass points of mass m are on the circumference of a circle with the same distance r to each other. At $t=t_0$ one lets go of the mass points and each of them moves within the ...
-1
votes
1answer
30 views

Velocity of a car in circular circuit

Prior apology for any violation of rules and regulation and poor expression of question. Statement: A racing car moves along a circular circuit with a constant speed of $20\text{ms}^{-1}$ in 5 ...
0
votes
0answers
30 views

How do I calculate the energy flux for this toroid?

My question is how do i calculate the total energy flux through the walls of the torus in this situation? The Poynting flux is given by $\vec{N} = \frac{1}{\mu} ( \vec{E} \times \vec{B})$ but the ...
0
votes
2answers
42 views

How can we prove that electric field originate from and terminate on charge using Gauss Law?

We already know that electric field originate and terminate on charge only and they doesn't make any closed path. But is it possible to prove this statement using Gauss Law ? If yes then how ?
0
votes
2answers
34 views

String wrapping around a motionless cylinder

A particle is connected to the end of a thin, weightless string, which has its other end connected to the cylinder, in such a way that motion of the particle causes the string to wrap around the ...
2
votes
3answers
42 views

Parallel-plate capacitor working voltage $V={Qd\over{\epsilon_0 A}}$ relationship with plates' distance

I don't understand why the working voltage of a capacitor increases with the plates' distance. Suppose we have 2 capacitors in series where $C_1=12,0\mu F$ and $C_2=4,0\mu F$. The voltage over both ...
0
votes
1answer
35 views

Angular momentum & Energy using Yukawa's potential

I was doing my Gravitation problems and I found this one that I'm unable to solve. Yukawa's theory for nuclear forces states that the potential energy corresponding to the attraction force ...
1
vote
1answer
62 views

Electric field of two infinitely long and thin, straight wires

I know the formula of the electric field, however: suppose that we put two infinitely long and thin, straight wires symetrically into the coordinate system, so that y axis is between them. Now ...
2
votes
1answer
27 views

When does light reach a shell observer in Schwarzschild metric?

I am trying to simulate the trajectory of light in the Schwarzschild metric (as seen by a far away observer) with fixed $\theta = \pi/2$. According to my source (Chapter 18, section 18.5) the ...
0
votes
0answers
26 views

Electric Flux through cube [on hold]

There is a cube with a charge at one of it's vertex(say A). What is the total electric flux and the flux through each face? I know the answer but not the solution. I don't think gauss law would help ...
2
votes
1answer
84 views

Angular momentum - proof for integer eigenvalues

I am confused about a proof my Quantum Mechanics textbook has left "as an exercise for the reader". So, we've got the angular momentum operator $\hat{L}$. We've also got the generalized angular ...
1
vote
0answers
28 views

Changing variables in a Lagrangian to obtain mass terms of gauge fields [on hold]

Context: In a excercise, consider a SU(2) gauge theory. The Lagrangian of the theory contains the three gauge fields and some scalar matter fields: $\phi_1 , \phi_2$ form a SU(2) doublet (fundamental ...