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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1
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1answer
16 views

Dropping a weight onto a spring scale

IfI drop a 5kg weight from a height of 1 meters onto a spring scale like many people have in their bathrooms. On impact the scale will show a higher weight than 5kg. Question: Which quantities factor ...
-5
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0answers
17 views

HOMEWORK HELP! Simultaneous equations (graphical method)

I just spent like half an hour on this and i am really not getting it. Any suggestions? A man buys 3 Ipods and 2 vouchers for £280 A woman buys 1 Ipod and 4 vouchers for £260 Form 2 equations from ...
0
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0answers
8 views

Computation of the partition function of a fermionic oscillator

I don't understand the following steps in the calculation of the partition function for a fermionic oscillator (Nakahara). The eigenvalues of the operator ...
1
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0answers
13 views

Continuum mechanics treatment of the Lariat Chain

Would anyone be willing to help me with a homework problem I'm doing? I've been working on the assignment all weekend and this one problem just will not click. I already have satisfactory solutions to ...
-1
votes
0answers
18 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
-2
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1answer
20 views

Finding gravitational acceleration question

I was working on an assignment and one of the questions is as follows: Find the value of g (the gravitational acceleration) on top of mountain $7.61~\text{km}$ above sea level. Assume that the ...
1
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1answer
14 views

Finding EPE at highest position for a vertical spring oscillator

Two identical vertical springs with a spring constant of 400N/m have a 5kg mass attached. (Let's assume length of the spring is like 15cm). Spring A oscillates with an amplitude of 10cm and B ...
0
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1answer
21 views

Disparity between two texts on intensity and phase interference - which is right?

So, I'm learning phase interference. Imagine we have two waves. $$ E_1 = A_0sin(wt) $$ and $$ E_2 = A_0sin(wt+\phi) $$ With $$ \phi = \frac{2\pi}{\lambda}dsin(\theta) $$ Which is the path ...
1
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0answers
21 views

How to add together non-parallel rapidities?

How to add together non-parallel rapidities? The Lorentz transformation is essentially a hyperbolic rotation, which rotation can be described by a hyperbolic angle, which is called the rapidity. I ...
-1
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1answer
34 views

How to calculate angular velocity given constant tangential acceleration?

A car starts moving in a circle with a radius of $200 \text{ m}$. It has a constant tangential acceleration of $1{\text{m}\over {\text{s}}^{2}}$. a. What is the angular acceleration? b. What is the ...
2
votes
3answers
91 views

Distance traveled by a water jet

I helped my kid in a science fair project, where we punctured holes in a water bottle at various heights and then measured the distance traveled by the water jets before they hit the ground. The ...
0
votes
0answers
28 views

Free body driagram of box and plate with a friction force on a smooth surface

On a smooth surface we have a plate of 40 kg and on that plate a a box of 10 kg. Between the plate and the box there is a ...
0
votes
0answers
33 views

How important is doing exercises in learning physics? [on hold]

I am a Chinese student who is currently studying physics at Nanjing university. And I just entered university a year ago. I am quite curious to know how you guys learn physics when you are in ...
0
votes
1answer
26 views

Determine normal forces on tilted table [on hold]

A table with the mass m, the height a and the width b is resting on a tilted floor with the angle of rake $\alpha$. A block at A prevents the table from sliding. Determine the normal forces from the ...
1
vote
0answers
16 views

Gamma matrices in Decay Calculations

I am trying to calculate the transition amplitude, $\lvert M^2\rvert$, for the process where a top quark (momentum p) decays to a bottom quark (momentum q) and a $W^+$ boson (momentum k). I am ...
0
votes
0answers
14 views

The angle of incidence of prism if emergent angle is 90°. Answer in terms of angle of prism and refractive index of prism [on hold]

A ray of light is incident at an angle of incidence i on one face of a prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is n, ...
0
votes
3answers
25 views

Path followed by a free test charge in an electric field region represent the electric lines of forces?

As we know that if we put any free test charge in an electric field which is moving horizontally then it will experience an repulsive force and move in that direction so by that we can say that for ...
2
votes
2answers
147 views

Why do electric field lines start and end at 90 degree at the surface of a conductor? [duplicate]

There is one property of electric lines of forces which states that: Electric field lines start and end at 90 degree at the surface of the conductor. But why is that so? Is there any proof for ...
2
votes
2answers
37 views

Work done by frictional force on a sliding block

A block slides across a table horizontally with an initial velocity $V$. The frictional force $F$ brings it to rest after its Centre of Mass covers distance $S$. What is the work done by the ...
0
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0answers
24 views

RC Circuit Analysis

I want to correct three misunderstandings about the following RC circuit. 1) How does current move directly after switch S gets closed? Current runs through all three circuit components to begin ...
-2
votes
0answers
16 views

Find magnitude of the net magnetic field at points A, B, and C between two parallel wires [on hold]

I've been having a lot of problems with this problem. Been working on it for over to an hour and nothing. I've been using amphere's law but I think I'm getting r wrong, here's one of my most recent ...
0
votes
0answers
22 views

Help with inclined slope motion? [on hold]

I have this question (5ii) and I was wondering why this wouldn't work, why can't I solve for acceleration using $v^{2}-u^{2}/2s$=$a$ then solve for $t$? I obviously have to resolve and use $p=fv$ but ...
1
vote
2answers
38 views

Electric field due to a finite line charge [on hold]

I was wondering what would happen if we were to calculate electric field due to a finite line charge. Most books have this for an infinite line charge. In the given figure if I remove the portion of ...
1
vote
1answer
77 views

When will the pringles can fall?

When I'm pushing a tall, cylindrical object stood on its end (like a Pringles can) I can push it near its bottom, and it will slide forwards, or push it near the top, and it will topple over. So, ...
2
votes
0answers
27 views

Current carrying conductor with a loop at a distance [on hold]

In Fig, there are an infinitely long conductive wire and a circle conductive loop C with the radius r and the number of turns n. The distance L between the wire and the loop is much larger than r, ...
0
votes
0answers
15 views

water pressure relationship to volume [on hold]

I have a one inch pipe 120 feet long and caped. I have a 60 pound input of pressure. I put a half inch pipe at the end and open it. What happens to the pressure in the one inch pipe? If I add another ...
1
vote
1answer
35 views

About shift operators

The question is this: Does $$L_+ L_- Y_{lm} $$ ,where $Y_{lm}$ is a spherical harmonic function, equals to zero. If so, why? The two operators above are defined as $$L_+ ={L_x + iL_y } $$ $$L_-={L_x ...
3
votes
1answer
29 views

Average force for repeated elastic collisions

I was asked to compute the average force exerted by a rigid spherical ball (mass m) on the floor over infinite time, in a situation where the ball is dropped vertically from a height (h) and makes ...
2
votes
0answers
23 views

Distribution forces

I've got two trees and between them is a rope. When someone about 100kg sits at the center of the rope, what are the forces on both parts of rope (to the left-hand side from the person and right-hand ...
1
vote
1answer
48 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [duplicate]

I want to know the configuration where the system would be most stable.I only know basic Physics & Maths and cannot start solving the problem.I can understand it for 4 charges and 6 charges as a ...
0
votes
0answers
23 views

Charged particle inside a hole in a charged layer

The layer $-a\le x \le a$ is homogeneously charged with a electric charge density $\rho \gt 0$ and on the x-axis a thin hole is made. A particle with mass $m$ and charge $q \gt 0$ move on the ...
0
votes
0answers
47 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [on hold]

I want to know the configuration where the system would be most stable. But I cannot think of a way to start solving the problem. I've solved it for 4 charges and 6 charges and they have a symmetric ...
1
vote
0answers
38 views

In Solution of the equation $\Box A_\sigma=0$. I find some mathematical difficulties [on hold]

The solution of the equation $$\Box A^\mu(x)=0$$ has the form $$A^\mu(x)=\int\frac{d^4k}{(2\pi)^4} e^{ik^\mu x_\mu}A^\mu(k)\delta(k^2).$$ Where we take $A^\mu(k)$ of the form $$A^\mu(k)=\sum ...
0
votes
1answer
33 views

Working out length of taut rope orbiting the earth remaining straight and radially directed [on hold]

A taut rope is orbiting the earth with angular velocity $a$. It remains straight and radially directed. If the midpoint is located at radius $r$, find the length of the rope. I can't even imagine ...
0
votes
0answers
32 views

How to calculate the potential energy of a magnetic dipole (with zero torque)

In the following problem, I would like to know how they arrived at their solution for finding the potential energy of a magnetic dipole (boxed in red). I understand I probably have to use the ...
-3
votes
0answers
21 views

Electric field calculation and its graph vs x [on hold]

Electric field along the line passing through two point charges, A point charge $Q_1= +3 \mu C$ is placed at the origin and a point charge $Q_2= -7\mu C $is placed at $x=0.4 m$ on the $x$-axis of a ...
3
votes
3answers
58 views

Does my (too low) tire pressure, affect the speedometer of my car?

Does my (too low) tire pressure, affect the speedometer of my car? How big is this effect?
0
votes
0answers
16 views

Nuclear medical physics [on hold]

How do you calculate the half life of daughter isotope (in secular equilibrium) Given a table of countrate(cps) and time (min). Like: Time (minutes) Count Rate (cps) time (min) Count Rate ...
-5
votes
0answers
30 views

Electric circuit question [on hold]

A 100W bulb is connected in series with a room heater.If now 100W bulb is replaced by a 40W bulb,the heater output will (Decrease) (Increase) (remain same)? And explain why?
0
votes
1answer
87 views

Commutator and Hamiltonian [on hold]

Assume that $[\hat{A},\hat{H}]_-=0$ and $[\hat{B},\hat{H}]_-=0$ but we know that $[\hat{A},\hat{B}]_-\neq 0$. Then there exists degenerate stationary states of $H$. How to prove it?
0
votes
1answer
30 views

Continuity equation for charge and current densities of an accelerated point charge

For a point charge that moves with the trajectory $ \vec r(t)$, we know that it has the singular charge and current densities $$ \rho (\vec x, t) = q \delta^3(\vec x - \vec r(t)) $$ $$ \vec J(\vec x, ...
0
votes
1answer
41 views

Determining the path of a light ray

Let's consider a ray in the plane $xy$. Let the refractive index be defined in any point of the plane with the function $n(x,y)$. In time $t=0$ the ray is located in coordinates $(x_0, y_0)$ and its ...
0
votes
0answers
24 views

Find the acceleration of a stirrer [on hold]

Question: There is a fixed 55 cm long rod (vertical) that is charged uniformly up to +137 nC, Place a 0.5 g plastic 6 cm long stirrer (horizontal) that is charge to +93 nC, 2.3 cm away from the rod ...
0
votes
1answer
29 views

Is this the correct entropy? [on hold]

In order to take a nice warm bath, you mix $50$ liters of hot water at $55^{\circ} C$ with $25$ liters of cold water at $10^{\circ} C$. How much new entropy have you created by mixing the water? What ...
0
votes
0answers
36 views

Find resistance of inductor in series RLC circuit [on hold]

We have a resistance of 350 Ohm, an inductor of 0.15H and a capacitor of 10 microfarad, connected in series to an AC source of voltage 240 V and frequency 50 Hz. The measured effective voltage over ...
0
votes
1answer
33 views

Derive the Sackur-Tetrode equation

How do you derive the Sackur-Tetrode equation? I know that you must start off with the multiplicity of a mono-atomic ideal gas: ...
-1
votes
1answer
28 views

Parabolic slide [on hold]

Can you give a big hint for this problem please? A material point is released at the end of a track in the form of a vertical arc of parabola $y = x^2$ in $[-1,1]$, the meter is selected as a unit ...
0
votes
0answers
29 views

Determine the speed of balls after collision [on hold]

I am sorry for my English it is not perfect at this moment but I hope you will understand my question. I have a problem with solving this exercise. The two balls of the same density and radius r and ...
1
vote
1answer
43 views

Circular motion from rest [on hold]

A particle $P$ is suspended from a fixed point $O$ by a light string of length $a$. When hanging at rest under gravity at $A$ it is given a horizontal velocity $u$. The particle moves freely in a ...
0
votes
0answers
40 views

Simple question. Where to find coefficients of friction? [on hold]

I am trying to calculate the force the Terracotta Warriors apply to the Lykan Hypersport in the Fast and Furious 7 movie. I am trying to find the frictional force of the statues applied against the ...