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2
votes
1answer
150 views

RMS Free Path vs Mean Free Path

I am trying to determine the mathematical difference between mean free path and root-mean-square free path. For an ideal gas, the relaxation time is $$\tau=\frac{1}{\sqrt2 \pi nd^2 \bar v}$$ and the ...
1
vote
2answers
237 views

Why does the induced EMF oppose the change in magnetic flux? Lenz's Law question

Can anyone explain to me why the induced magnetic field will oppose the change in magnetic flux? Is it an energy thing? I know that the induced emf is $$ emf= - \frac{d\phi}{dt} $$ but my book ...
0
votes
2answers
56 views

Find the tangential acceleration

A racing car driver drives his car on a flat circular track of radius $\frac{25}3 m$ and a coefficient of friction $0.5$. Find the magnitude of its tangential acceleration (in $ms^{-2}$) at an ...
2
votes
4answers
266 views

Charge distribution on plates

$A,B,C$ are $3$ identical metallic plates. Initially, charges $Q$, $4Q$ and $2Q$ were given to $A$,$B$ and $C$ respectively. Find final charge distributions when $B$ was earthed and $A$ and $C$ were ...
0
votes
0answers
51 views

Deduce magnetic field based on electric field

I'm learning Maxwell's electromagnetic equations and i can't wrap my head around this problem: Given the volume $x\in [0,1], y\in [0,1], z\in [0,1]$, electric field $\vec E(x,y,z,t)$ and material ...
1
vote
1answer
87 views

Duration of Satellite orbit in the shadow of the Earth

I want to determine how many minutes a satellite is in a circular orbit around the Earth at about $1000 km$ altitude. I assumed that the Sun-Earth vector lies exactly in the orbital plane of the ...
1
vote
3answers
288 views

What is a linear probability density function?

In the following question, what is meant by linear probability density function? Is it a uniformly distributed variable or triangularly distributed? Thanks in advance. The kinetic energy of any ...
1
vote
1answer
56 views

Circuits and Power

"The diagram below represents a simple circuit composed of 5 identical light bulbs and 2 flashlight batteries. Which bulb (or bulbs) would you expect to be the brightest? a) V only b) V and W ...
0
votes
1answer
124 views

Latent heat of vaporization

The molecular weight of water is 18.015 gram. The number of moles of water in one liter (1000 gram) will be: $3.34\times 10^{25}$ molecules (in 1kg). We know that latent heat of vaporization of water ...
0
votes
1answer
47 views

Expectation value of Hamiltonian on number state [closed]

Hamiltonian is defined by $H_I = \hbar \omega (\hat{a}^+ \hat{a} + 1/2)$ What is the expectation value of the energy on the number state $$\vert \psi \rangle = \frac{1}{\sqrt{2}} ( \vert 1 \rangle ...
0
votes
1answer
128 views

Ball thrown in a moving train [duplicate]

A ball is thrown upward in a train moving with a constant velocity. Where will it land? My intuition tells me that the ball will fall at my back. But my book says that it will return back to the ...
0
votes
2answers
94 views

How is $\text{PE} = qV$ derived using knowledge of $F = \frac{q_1q_2}{4\pi \epsilon_0 r^2}$

I recently started grade 11, and this concept confuses me, since if we place a charge $q$ on a potential $V$, I do not completely comprehend what values would need to be substituted which would give ...
0
votes
0answers
31 views

Self-inductance of a toroidal inductor

I am trying to determine the self-inductance of a toroidal coil of mean radius $R$ with $N$ loops of radius $a$ with a current $I$ flowing within them. I have calculated the magnetic field by noting ...
0
votes
1answer
45 views

A pearl that moves in a smooth vertical hoop

I wanted to ask about the situation of a pearl that moves in a smooth vertical hoop in circular motion as described in the following sketch. According to a simulation found in the internet , a ...
0
votes
1answer
94 views

How to derive the commutation relationship between $\hat{L}^2$ and $\hat{\textbf{p}}$ [closed]

How to prove that $$[\hat{L}^2,\hat{\textbf{p}}] = i\hbar(\hat{\textbf{p}}\times\hat{\textbf{L}} - \hat{\textbf{L}} \times \hat{\textbf{p}})$$ I tried to expand $\hat{L}^2$: ...
-2
votes
1answer
78 views

Question on kinematics [closed]

A particle is projected vertically upwards from point $A$ on the ground. It takes $T_1$ time to reach point $B$ but it still continues to move up. If it takes further $T_2$ time to reach ground from ...
0
votes
1answer
95 views

One problem on Classical Mechanics [closed]

I'm wondering why in this problem I can't apply newton second law? The mass $m$ of the moving part will be the mass solved in the problem.
0
votes
0answers
19 views

Do I ever not account for temperature variation from wall temperature in pipe flow?

Let's say I have internal pipe flow with a constant wall temperature. If I evaluate the properties at either the mean inlet temperature of the average of the inlet and outlet, do I always have to ...
3
votes
0answers
40 views

How much weight is lifted from each side? [closed]

I don't know the math to do this, so I am asking here if someone can work this out with all of the details I'm providing. Total mass EST.: 2,400 lbs. Length from front to back: 14 feet 6 inches. ...
0
votes
1answer
42 views

A pearl that moves in a smooth vertical hoop (Circular motion) [closed]

I couldn't understand something about the situation of a pearl that moves in a smooth vertical hoop in circular motion. When the normal force equals 0 , the pearl didn't disconnect from the smooth ...
1
vote
1answer
79 views

How to calculate distance travelled from velocity vector and angle? [closed]

I am trying to get the distance a projectile travels, so I can display it in my program. I'm sort of new to physics, but I've tried looking this up. I'm not getting the right results however, and me ...
0
votes
1answer
51 views

Calculating electric potential from a changing electric field

Assuming that I calculated the electric field in a single point between a uniform charged positive sphere and an infinite long wire charged positive uniformly. Now, I want to calculate the velocity of ...
1
vote
0answers
78 views

Restrained double pendulum

The equations of motion of a double pendulum are well-known. Usually you'd have the them expressed in the rotations $\theta_1(t)$ and $\theta_2(t)$. There are two degrees of freedom. Now consider the ...
0
votes
2answers
68 views

Molecular mean free path probability

Let's let $p(\xi)$ be the probability a molecule travels at least $\xi$ between collisions, lets say $\xi=0.01$. When I think of this statement, I think it it is the probability the molecule is able ...
0
votes
0answers
48 views

Trace of Spin Products Using Rotation operators

So I am working on this problem involving the trace of spin matrices. I am trying to solve for $Tr(S_iS_j S_kS_l)$ using rotation operators. I know how to go about solving for $Tr(S_iS_jS_k)$. It is ...
0
votes
1answer
74 views

Total momentum in linear monoatomic chain

Context: Solid state physics. Monoatomic linear chain. Question: To prove that the total momentum of the chain is zero. Attempted solution: I consider the sum: \begin{align*} p = \sum_{n=1}^{N} m ...
0
votes
1answer
59 views

Calculating a radioactive sample's mass from its activity [closed]

The question reads as such: "What is the mass of a 1.05 µCi carbon-14 source?" First I convert to decays/s: $R = 1.05 µCi=3.885 \times 10^4 decays/s$. The half-life for carbon-14 that we've been ...
2
votes
4answers
84 views

Acceleration and Circular Motion

Lets assume that there is a force that makes our body moves in circular motion. We know that the acceleration of a body that moves in circular motion is Velocity ^ 2 / Radius . How is it ...
1
vote
2answers
119 views

Finding power with Drag Force equation

The mass of the car is 1500 kg. The shape of the body is such that its aerodynamic drag coefficient is $C_D=0.330$ and the frontal area is $2.50 m^2$. Assuming that the drag force is proportional to ...
4
votes
2answers
197 views

Electric field in a sphere with a cylindrical hole drilled through it

Suppose that you have a sphere of radius $R$ and uniform charge density $\rho$; a cylindrical hole with radius $a$ ($a\ll R$) is drilled through the center of the sphere, leaving it like a "necklace ...
1
vote
1answer
47 views

Determination of entangled states

The definition of an entangled state $|\Psi\rangle$ is that it CANNOT be factored into $$|\Psi\rangle=|\psi\rangle_1\otimes|\phi\rangle_2$$ I am kind of confused on what is meant by a quantum ...
1
vote
1answer
217 views

What are the general solutions to a hard sphere collision?

Surely someone has found the solutions to the hard sphere collisions (in $n$ dimensions) of two bodies of mass $m_1$ and $m_2$, respectively--that is the resultant velocities (or momenta) of the two ...
0
votes
1answer
54 views

Ohms Law Voltage/Potential Difference [duplicate]

Three 2.0 Ω resistors are connected in series to a 12 V battery. What is the potential difference across each resistor? � This question requires Ohms law because V is needed right? So I would use I = ...
1
vote
0answers
49 views

Fraunhofer Diffraction [closed]

A 1-dimensional aperture is illuminated by a parallel beam of light of wavelength $\lambda$ and the diffraction pattern is viewed on a distance screen. Show that the amplitude of the diffraction ...
0
votes
0answers
26 views

Question regarding 2 conducting spheres connected by a long fine line (electric potentional)

I'm having a bit of trouble understanding a pretty simple issue. Assuming I have 2 conducting spheres uniformly charged connected by a long fine line (as shows in the added photo) and im being asked ...
0
votes
3answers
131 views

Time dilation in special relativity

Suppose a star ship is moving with some velocity. Two light pulses one in direction similar to star ship another opposite to it is shot towards the space ship. Then how time inside space ship adjust ...
1
vote
1answer
85 views

Quantifying the current drawn by a motor at half speed

I have a h/w question regarding the current in the armature of a motor when it is operating at half it's normal speed. The question is; A motor is designed to operate at 118V and draws a current ...
1
vote
2answers
123 views

Force between two charged particles [closed]

Consider two positively charged particles, one of charge $q_0$ (particle 0) fixed at the origin, and another of charge $q_1$ (particle 1) fixed on the y-axis at $(0,d_1,0)$. What is the net force ...
1
vote
1answer
60 views

High-School Physics with inclines [closed]

The figure below shows two blocks with a rope that runs over a pulley. The mass of $m_2$ is 5.0 kg and the incline is 35 degrees. The coefficient of static friction between $m_1$ and the inclined ...
3
votes
0answers
61 views

Feynman Toy Model Constraints on Number of Each Kind of External Lines

(From my homework) In our toy model we have three kinds of spinless particles: $A$, $B$, and $C$. The primitive vertex of decay/interaction is shown below: My actual problem statement says: ...
3
votes
1answer
83 views

Thermodynamic relations

I'm asked to establish the following relations: $\left( \frac{\partial C_V}{\partial V} \right)_{T,N} = \frac{T}{N} \left( \frac{\partial^2 P}{\partial T^2} \right)_{V,N} $ $\left( \frac{\partial ...
1
vote
1answer
114 views

Question about buoyancy

I took an empty clear sphere with radius r, put some weight inside this sphere, and put in into the water. I calculate the buoyancy force as: Volume of the sphere = Volume of the water displaced ...
1
vote
1answer
58 views

Work done (by gravity) on paired blocks [closed]

Why does gravity do more work on the block going down? The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?
2
votes
3answers
425 views

Force on a point charge q inside a cavity in an uncharged conductor

This is problem 2.40 from Introduction to Electrodynamics by D. J. Griffiths: A point charge $q$ is inside a cavity (not necessarily spherical or anything similarly regular) in an uncharged ...
0
votes
0answers
36 views

Magnetic forces and generators

i'm really struggling to break this question down into manageable chunks and identify which quantities are relevant. I'm also unsure of some of the wording in the question. A bar of length ...
1
vote
0answers
37 views

Stationary wave on a string

The problem says: A string lies on the x-axis, and is fixed at $ x=-a $ and $ x=a $. At $ t=0 $ we impose a transversal velocity given by $ a^2-x^2 $. Assuming that the velocity of the wave is $ c ...
1
vote
3answers
362 views

How to calculate new air pressure with temperature change? [closed]

The question: The gauge pressure in your car tires is $2.60 * 10^5 N/m^2$ at a temperature of $35.0°C$ when you drive it onto a ferryboat to Alaska. What is the gauge pressure later, when the ...
2
votes
0answers
86 views

Is my method of calculating thermal conductivity of a metal wrong?

I am trying to determine the thermal conductivity of pure copper at various temperatures using the Weidemann-Franz Law but for some reason it is not matching up to textbook data. I used the Bloch ...
1
vote
1answer
59 views

Help understanding the solution to a problem regarding kinetic energy of a group of point charges

The problem provided by my professor goes as follows: "Now consider a situation in which all charges are equal to q and they simultaneously become "unglued". What speed will each charge have when a ...
0
votes
2answers
145 views

Is it possible to calculate how fast something will roll down a hill?

If I have a wheel, I know it's mass and diameter and the slope of a hill. Can I calculate the time it will take to get to the bottom of the hill? I am doing a project for my science fair and I sent 5 ...