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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Uniform field through a disc

Let us say that we have a magnetic field of the form $B_0 sin(\omega t) \hat e_z$ in all space. Now let us say we put a conducting disc within this field. I want to find the electric field within this ...
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0answers
10 views

what is the charge and current density in system K2?

Consider there are two inertial reference of frames K1 and K2 in which K2 is moving with the boost velocity of V in direction of X2. If someone at the rest in system K1 finds the charge density $ \rho ...
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0answers
11 views

Finding velocity field of spherical bubble in incompressible fluid

A spherical bubble in an incompressible fluid of density $\rho$ has radius $a(t)$. Write down an expression for the velocity field at a radius $R > a$. The pressure far from the bubble is ...
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0answers
19 views

Quark and anti-quark number density [on hold]

Im trying to solve this question but having little luck in doing so. Would appreciate if someone could help me out!
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0answers
13 views

What is the speed of the panel when the spacing between the plates increases [on hold]

Flat-panel capacitor WITH the surface area of 200 cm2 is connected to the voltage 1000 V. One of the plates we start to move away from a constant force 5.10-4 Newtons. the spacing between the plates ...
3
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1answer
39 views

Special relativity kinematics problem

I have this problem in SR kinematics. a spaceship travels near earth at c/2. it shoots off a light-ray at 45deg to its direction of travel (measured in its own ref frame). What is this angle in the ...
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1answer
26 views

Finding the tension in a rope with mass defined per unit length [on hold]

A rope of length L has its mass per unit length λ varies according to the function λ(x)=e^x/L. The rope is pulled by a constant force of 1N on a smooth horizontal surface. Find tension in the rope at ...
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2answers
39 views

What should the length of my wire be in order to get a surface area of 10cm^2?

I would like to make a flat coil out of a steel wire that is 1.22mm in thickness (or 1.22mm in diameter). I wish to make the coil up the wire into a flat disk that has a surface area of 10cm^2. What ...
2
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1answer
33 views

Boltzmann equation in cosmology

I have a question about the Boltzmann equation in cosmology. Im trying to understand how this can hold? Where does the logarithmic terms come from? It is explained quite well here ...
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0answers
29 views

What is full of energy satellite is in orbit around Jupiter? [on hold]

Please I post here since I am a new member and do not have 5 reputation as required. Thanks for understanding. ................. In 2003 it was derailed from orbit so that it crashed on the planet. ...
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2answers
60 views

Gravity - change with altitude

Does acceleration due to gravity, $g$, which is calculated by Newton's equation, decrease with altitude? Forgive the silly question.
2
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1answer
38 views

Work in gravitational field

I was doing a test a few days ago and there was a fairly simple task involving gravity basics. The task asks me to calculate the work done by moving an Earth's artificial satellite from a stationary ...
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1answer
35 views

Relativistic Lorentz Force with constant, perpendiuclar, and uniform E and B fields

I am trying to solve the following problem from the Fundamentals of Plasma Physics by Bittencourt (Problem 2.7): Analyze the motion of a relativistic charged particle in the presence of crossed ...
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0answers
16 views

A force in a homogeneous magnetic field [on hold]

Semi infinite parallel conductors, while on them without friction slides a crossbar . Perpendicular the plane of the conductors is a homogeneous magnetic field. To what extent of force we must act on ...
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1answer
17 views

Magnetic field at a distance from a metal rod [on hold]

A massive metal rod of 4 cm has a current of 8000 A running through it and the current density is uniform. What is the magnetic field a distance 1 cm from the rod? Should I use the Biot Savart law and ...
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1answer
52 views

Why can this question about Centripetal Force not be answered in this way?

Here is the question: "A car travels round a bend which has radius $100 m$ and is banked at an angle of $20°$ to the horizontal. The car is travelling at a speed of $30 ms^{-1}$. What is the least ...
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1answer
18 views

Period of a spring in SHM (simple harmonic motion)

An object with unknown mass M is hanged on a vertical spring with unknown spring constant K, the spring is in rest and is 14 cm from its normal point (if it didn't had the mass hanged it had less 14 ...
0
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1answer
16 views

combination of mirror and lens [on hold]

a convex lens forms a real image of a point object at a distance of 50 cm from convex lens. a concave lens is placed 10 cm behind convex lens on image side. on placing a plane mirror on the image side ...
0
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1answer
12 views

Condition for sliding of two blocks placed one over another and connected by spring

A constant force F is applied to smaller mass till M slides. The spring constant is k. Now it is asked to find k. I'm confused with the condition at which the block will start sliding. Can ...
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1answer
43 views

Where does this relativistic relation involving the delta function come from?

\begin{equation} \int\delta(E^2-\mathbf{p}^2-m^2)dE=\frac{1}{2E_\mathbf{p}} \end{equation} Shouldn't integrating the delta function like this just give 1?
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0answers
21 views

physics numerical on vectors [on hold]

Question:- The sum of the magnitudes of two forces acting at a point is 18 N and the magnitude of their resultant is 12 N. if the resultant makes an angle of 90° with the force of smaller ...
0
votes
1answer
21 views

Total potential energy for two charged particles

I'm trying to formulate a Lagrangian equation for a system of two charged particles. They have respective masses $m_1$ and $m_2$, and respective position vectors $\vec{x_1}(t)$ and $\vec{x_2}(t)$. ...
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1answer
33 views

Question about Gauss' law and dipoles

I've got a question about dipoles and Gauss' law: Consider an electric dipole $p=ql$ in free space, centred at the origin of a Cartesian reference frame. Using Gauss’s Law, discuss if the electric ...
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0answers
25 views

Work done by a gas in an expansion [duplicate]

1) Consider a gas expanding quasistatically and reversibly from $V_1$ to $V_2$ at constant temperature. I want to calculate the work done. So by convention work done by a system is a negative quantity ...
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0answers
25 views

How to find the generators of a deformed boost?

I'm reading the paper arXiv:gr-qc/0012051 on doubly special relativity. In page 7, the author wants to find the generators of a deformed boost that preserves $$E^2 = p^2 + m^2 - l_p p^2 E$$ ($l_p$ is ...
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0answers
8 views

Path of puck through a turntable

I was looking a problem which tells me to consider myself standing on the ground beside a perfectly flat horizontal turntable rotating with constant angular velocity w. Then I lean over and shove a ...
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0answers
24 views

Kinematics Question - Motion in two dimensions [on hold]

Suppose there is a 11. 7 ft wide ditch with the approach roads at an single of 15 degree with the horizontal. If the length of bike is 5 ft and it leaves the road when the front part runs out of the ...
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0answers
14 views

Heat energy question [on hold]

An aluminium block of mass 1 kg is heated by an electric heater for 3 minutes and a temperature rise of 15 °C is recorded. If the electric heater is connected to a voltmeter which gives a reading of ...
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1answer
21 views

An example on computing the density of a typical nucleus

An example from my text is as such: Compute the density of a typical nucleus, and find the resultant mass if we could manufacture a nucleus with a radius of 1cm. I will only provide a partial ...
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0answers
40 views

Why they put rocks in Railway tracks? [on hold]

Why they put rocks in Railway tracks? Each time i see there are many rocks are there in railway tracks, but what is the purpose of putting rocks?
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2answers
40 views

Static friction and Kinetic friction

I can't seem to find this anywhere on the internet or on stack... Sadly. Very basic question: I have a block that is on a surface. The coefficient of static friction between the two is $0.3$, ...
-1
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0answers
19 views

What is the speed of the charge in this setup of spherical conductors? [on hold]

Two concentric spherical conductors respectively have radius $r_1 = 0.145\ \mathrm{m}$ and $r_2 = 0.207\ \mathrm{m}$. The inner sphere carries a charge of $-6.00 \cdot 10^{-8}\ \mathrm{C}$ . An ...
-1
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0answers
20 views

Classifying solutions of equation of state as functions of temperature [on hold]

I've got an exam in 2 days and the past papers don't have solutions. I'm given this equation of state: $$ p + a\frac{N}{V} = \frac{Nk_BT}{V-bN}$$ and asked to classify the solutions as functions of ...
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0answers
23 views

Semi infinite parallel conductors [on hold]

Semi infinite parallel conductors separated by a distance of 0.5 m are at the endpoints associated with the resistance R = 4, while according to the two without friction slides bar by weight: 0.1 kg ...
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0answers
26 views

In the solar system are located planet A and B [on hold]

in The solar system are located planet A and B. A and B are their heliocentric distances distance. A is planet on the outer = 1 a: e: and bypass -Time PA = 365 days. Assuming coplanar orbits. A ...
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0answers
23 views

Find the equivalent capacitance [on hold]

On the plane capacitor below, the surface of the boards is $A$ and the distance between the boards is $d$, the dieletrics constants are $k_1$ and $k_2$. Find the capacitance of the capacitor in ...
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0answers
34 views

One extra conservation equation or angle relation for a relativistic collision

Edit: It seems that the derivation for the center of momentum frame was incorrect, due to the fact that the center of momentum velocity changes after the collision. This is also true for the ...
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2answers
32 views

Find the total current supplied to the circuit [on hold]

I tried but could not manage to find the correct equivalent resistance. Please tell the process. The answer is 3A
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0answers
10 views

Expression for the heat capacity of an ideal Bose gas

I've been desperately looking to solve this problem through various mathematical tricks but it seems that there's something that I'm missing here. Consider an ideal Bose gas. If one notes the ...
1
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0answers
24 views

Find the time needed to warm the water to a temperature [on hold]

An electrical resistence has a power of 1 kW. It is put inside a container that has 10 liters water. The water is in temperature 20C with pressure 1 atm. Find the time to warm the water to the ...
0
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0answers
17 views

Find the molar specific heat for each gas [on hold]

A mixture of two ideal gases, the first one atomic and the second two atomic are put in normal conditions in a calorimeter with volume 1 liter hermetically closed. After it is given 10J thermal energy ...
1
vote
1answer
34 views

Find the velocity of the escape of the bullet

A gun has a muzzle 0.8 meters long and with a diameter of 0.006 m. A bullet with mass 0.002 kg is initially 0.01 m away from the end of the muzzle. As a result of a gunshot, the pressure of the gas ...
-1
votes
0answers
45 views

Electric field outside a sphere

The sphere $K\subseteq R^3$ with radius $R$ has a homogeneous charge density $\rho$. Find the electric field E, produced by K outside of, meaning, find the integral ...
-1
votes
2answers
89 views

What does this equation mean? [on hold]

So I have just entered 11th grade and started limits on my own but my Physics textbook has an equation which I don't understand, I suspect it uses integration which I haven't learned yet. So can ...
0
votes
1answer
15 views

What is the fraction of the incident intensity passing through polarized sheets?

Unpolarized light is incident on a set of three polarizing sheets as shown in the figure at right. The polarizing directions of the sheets make angles 10°, 55° and 85° to the vertical. What fraction ...
0
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0answers
20 views

Would any interference maxima be missing in the double slit experiment? [on hold]

An aperture of 0.9mm of double slit forms a diffraction pattern on a screen placed 6.0 meters away when illuminated with light of wavelength 600 nm; the distance between two slits are not specified. ...
0
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0answers
20 views

Amplitude of electric field produced by satellite dish [on hold]

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
14 views

Relation of current with frequency and voltage [on hold]

I tried to solve a numerical problem but I got stuck and I think it very necessary I will drwa certain basic conclusions when I would found its solution. The question is: An incandescent lamp ...
0
votes
1answer
16 views

Derivation of impedance matching formula

When matching impedances with a quarter wavelength coupler, how do I derive that its impedance has to be $$ Z_2=\sqrt{Z_1 Z_3} $$ where $Z_1,Z_3$ are the impedances of the adjacent materials?
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0answers
13 views

Calculating work needed to move a charge between plates of an uncharged capacitor [on hold]

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 ...