Disk Definition and 819 Threads

Hello I'm having trouble finding the right way to apply Faraday's law to this question. I've found the flux through the disc: ##\phi = \vec A \cdot \vec B = B_{0} \sin{\omega t} \left( \frac D 2 \right)^2 \pi ## and the EMF: ##\varepsilon = - \frac {d \phi} {dt} = -B_{0} \omega \cos{\omega t}...

The problem is to solve for the area R. Can you please help me ? I have tried to do it many times. Thank you in advice.

Can you please help me ? I have tried to do it but I end up getting the wrong answer.

Hi everyone This is a quick Q but I don't understand why I got it wrong This is what I have done Could anyone let me know where I went wrong? Thanks for any help!

My attempt at a solution is shown in attached file "work for #10.png". I used Desmos Scientific online calculator to obtain my final answer.

I would like if my procedure is correct ... Due to the symmetry of the problem, I only worry about the vertical coordinate of the field, so I will work with the magnitude of the field, and I will treat the problem in polar coordinates. ##E= \int_{R_1} ^ {R_2} \int_{0} ^ {\pi} \frac {\sigma...

Why do they only think of kinetic energy of motion? Why don't they think of both kinetic of motion and kinetic of rolling energy? So. i think ## L = \frac{1}{2}mv^2 + \frac{1}{2}I \omega^2## ## L = \frac{1}{2}m(r \omega)^2 + \frac{1}{2}(\frac{1}{2}mr^2) \omega^2## ## L = \frac{3}{4} mr^2...

Popular Physics. "Evidences of the earliest Supernova observation in the Nebra disk R.G. Pizzone" ---- https://arxiv.org/abs/2005.07411I know this isn't exactly breaking news and I cannot comment of the quality or validity of the research, but I've found that due to the brevity of the paper...

From a freebody analysis I got, $$ \vec{r} \times \vec{F} = |r| |F| \sin( 90 - \theta) = (R-r) mg \cos \theta$$ and, this is equal to $$ I \alpha_1$$ where the alpha_1 is the angular acceleration of center of mass of small circle around big one, $$ I \alpha = (R-r) mg \cos \theta$$ Now...

The first part is easy, we have 2T= Mg T= 0.5 Mg Now for the second part where I'm having trouble understanding Morin's solution: I take the normal force on a small circle arc to be N, we know that the y component of the normal force must be balance with Mg for the whole disk, therefore Ny =...

-------------------------------------------------------------------------------------------------------------------------------------------------- This was a problem introduced during my classical electrodynamics course. I am not 100% sure, but I think I've solved up to problems (a) and (b) as...

Hi to all member of the Physics Forums. I have this question: it is possible consider the analogue of the Schrodinger equation on the plane with configuration space ##(x,p)\in\mathbb{R}^4## on the complex disk ##\mathbb{D}=\{z\in\mathbb{C}: |z|<1\}##? Ssnow

Basically, there is a gravitational field g and a friction force acting on the cylinder, which does not slip in the plane. The question is, the acceleration of m'. I solve this question basically by this: " m*g*dh*sina + m'*g*dh = m*v1*dv1 + m'*v2*dv2 + I*w1*dw1 " {1} w*r = v1' + v2' So The...

I did the first step pretty well, and the answers match, but i don't understand why in the second case the period changes.

Neeleman, M., Prochaska, J.X., Kanekar, N. et al. A cold, massive, rotating disk galaxy 1.5 billion years after the Big Bang. Nature 581, 269–272 (2020). https://doi.org/10.1038/s41586-020-2276-y Abstract Massive disk galaxies like the Milky Way are expected to form at late times in traditional...

I was always a little confused about the rolling down of a body, let's say, a sphere. It's know that to body rotate, from the rest, in a referential frame on the ground [inertial], is necessary a friction, that will just act like a medium that transforms kinetic energy of translation into...

A disk is dropped on a platform rotating at a constant angular speed ##\omega_i## as shown below. The question asks whether the final kinetic energy of the platform is conserved. I understand the angular momentum is always conserved provided that the net torque is 0, so I wrote the following...

Hi everyone, I need help for this homework. I'm a mechatronics engineering student and i want to solve this question but no matter how hard I try, I can't solve the question. Sorry for my bad english...The disk connected to the AB stick with a length of 2 meters is rolled as shown in the figure...

There is no net external torque since the cylinder is slipping (no friction), so the angular momentum should be conserved. $$L_f=\frac 12MR^2\omega_i=\frac 12\times3.8\times0.52^2\times50\times\frac{2\pi\times0.52}{60}$$

I know that a hoop should have a higher rotational inertia than a solid disk because its mass is distributed further from the axis of rotation. What I don't understand is how a disk of the same mass and radius can have a higher rotational inertia. If the objects roll freely their axes of...

Hi, I've been stuck for a long time with this exercise. I am not able to calculate the potential vector, since I do not know very well how to pose the itegral, or how to decompose the disk to facilitate the resolution of the problem. I know that because the potential vector must be parallel to...

Let ##\Theta## be the angle, following the movement of the center of the disk. In order to find the kinetic energy, we brake the movement of the disk into 2: The translation of the center of mass, and the rotation of the disk around it. So, the kinetic energy will be given by: $$T= \frac 1 2...

Can I use a brand new removed SSD HardDisk to store data without doing any thing at the beginning time(e.g without formating or other things)?I will use SSD to store ebooks(PDF,Djvu,epub,Audio files). Can I open books when I attach the removed SSD to laptop?

Not sure how they obtained an answer of (2meukenetic *Mg/R^2)*r^2 dr = dt When they say disk I am assuming it's not ring shaped. So since F * Dr= DT where I guess F acting on a small point on the disc is constant from the table top. And Dr is the variable distance from a random small point from...

moment of inertia= [(1/2)(1.1kg)(0.96)^2+ (1.1kg) (0.75*0.96)^2]= 1.08 kg*m^2 θ=9.8 degrees= 0.17 rad torque= (mass*gravity) * radius * sin(theta) radius= 0.17rad * 0.96m = 0.16m torque= (1.1kg*9.8m/s^2) * 0.16m * sin(0.17rad) = 0.29 N*m torque = inertia * angular acceleration 0.29N*m=...

Does anyone know if the eigenfunctions of the Airy disk function (or Bessel function) \frac{J_1(x)}{x} has a closed form?

For this problem, since the weight force on the "particle" (child) is not always aligned with the tangential circular path of the disks, I couldn't think of a way to use rotational kinematics equations. As such, I tried to solve the problem using work principles (namely, that the change in...

So I'm reviewing old lectures to prepare for an exam soon. This is about polarization. E fields, D Fields, etc. My professor labeled this diagram like so. The figures my professor drew are cavities in a dielectric if you can't read her handwriting. However, I can't seem to figure out why the...

Since torque= |force||radius|sin(theta) : î = |71E6||5000m|sin(30)= 177.5E9 N*m ĵ = |0||5000m|sin(30) = 0 k̂ = |-158E6||5000m|sin(30)= 395 N*m

My answers so far are: a) J=I/(2*pi*r*t) b) u=J/ne=I/(2*pi*r*t*n*e) c) F=IB/(2*pi*r*t*n), in theta direction (polar coordinates) d) This is where I am stuck. I understand the example for motional emf with a rod moving through a magnetic field but I'm not sure how to apply it to this scenario...

As I`` m learning for an upcoming exam I found an electrodynamics problem I struggle with. In the first task I need to calculate the magnetic dipole moment of a uniformly charged,thin disk with the Radius R and a total charge Q which rotates with a angular speed omega round its symmetry axis...

I can calculate the angular speed but I don't know how to calculate the radius. Is there certain formula to calculate it? Thanks

Homework Statement: uniformly charged disk, radius r, with surface charge density ##\sigma## . I want to find the electric field along the axis through the centre of the disk at a h distance Homework Equations: ##dE=\frac {kdq}{r^2}## My Solution: ##dE=\frac {kdq}{r^2}## in this case r=s...

I used the above equations to solve for tension, torque, inertia, and angular acceleration. Are the formulas I used correct for the given system? How can I calculate Inertia from the trendline equation, I'm drawing a blank.

Hello! Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object. DM particles could be trapped and settled in around...

In Calculus II, we're learning about solids of revolutions and computing their volumes. I'm unsure when to apply the appropriate methods and how to make the correct partitions. Please tell me if my reasoning is correct: The disk/washer method is applied when your partitions are perpendicular...

Homework Statement A capacitor consists of two large metal disks placed a distance ##s## apart. The radius of each disk is R ## (R \gg s)## and the thickness of each disk is ##t##. The disk on the left has a net charge of ##+Q## and the disk on the right has a net charge of ##-Q##. Calculate...

Hello, I am trying to find an analytical expression to determine the solid angle subtended by a disk source onto the face of the cylinder. I will appreciate if someone can provide me directions. I am aware how to calculate solid angle by a point source to cylinder's face ( omega =...

A giant ice disk, almost perfectly circular, has formed in the Presumpscot River in Westbrook, Maine: https://www.npr.org/2019/01/16/685816019/a-massive-moving-ice-disk-takes-center-stage-mesmerizing-maine As it slowly rotated, contact with one shore smoothed away the irregularities at its edge.

Homework Statement [/B] A train stands in the middle of a rotating disk with an initial angular velocity of $\omega_i$. The mass of the train is m and the moment of inertia of the train-disk is I. At one point the train departs on a straight track to a distance R from the disk's centre. (R...

The Oort cloud is often drawn as a sphere. Everything in it orbits the sun in circles or ellipses. Since the shape is not a disk, collisions are expected. Why hasn't the Oort cloud converged to the more stable, collision-free, disk shape?

Homework Statement A titanium disk (with ##E=107 ~GPa##, Poisson's ratio, ##v=0.34##) precisely ##l_0=8~mm## thick by ##d_0=30~mm## diameter is used as a cover plate in a mechanical loading device. If a ##P=20~kN## load is applied to the disk, calculate the resulting dimensions, ##l_{01}## and...

Homework Statement [please see attached photo] Homework Equations [please see attached photo] The Attempt at a Solution [please see attached photo] The issue for me starts with (but probably doesn't end with) replicating the velocity equation using the Conservation of Energy equations. Is...

Hi all, This is not exactly a homework question, more like for my own safety So I have a project going on and I need to use an angle grinder without the safety guard which will be enclosed in a box (made from plastic most probably). So I decided to check if the plastic box would be able to...

Hi to everybody! Please: can you help with this problem? A conductive disk with a radius a = 20 cm, with negligible moment of inertia, rotates around its horizontal axis. The disc region around the radius is inserted in a magnetic field B = 0.75 T perpendicular to the disk itself. A mass is...

Homework Statement Consider a rod of length ##L## and mass ##M## attached on one end to the ceiling and on the other end to the edge of a disk of radius ##r## and mass ##m##. This system is slightly moved away from the vertical and let go. Let ##\theta## be the angle the pendulum makes with the...

Homework Statement a)recall that electric potential is a scalar quantity. For a circular ring of radius, R', carrying charge, Q, what is the electric potential at a height,y, above the center of the ring? b)Use your above answer to determine the electric potential at a height,y, above the...

Homework Statement Working through Purcell (among others) as fun applied math/math modeling refresher. But, I have struggled all week in establishing from first principles that the potential/field/distribution for a configuration of two capacitive disks of radius 1 and separation s along the...

<< Thread moved from the technical forums, so no Homework Help Template is shown >> I have mind boggling problem, trying to distinguish between Dynamic reaction versus Coriolis acceleration of thin hoop. Problem: A thin, hoop of mass m and radius r spins at the constant rate ω 1 about an axle...

Homework Statement At what distance, a, along the axis of a uniformly charged disk of radius R is the axial electric field strength equal to one half its value at the surface of the disk at the center. Homework Equations electric field of disk (attached) The Attempt at a Solution First I...