What is Disk: Definition and 816 Discussions

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  1. T

    Finding the speed of a disk after being hit by a bullet.

    Homework Statement A .01kg bullet traveling at 800m/s hits a disk with a radius of R=.1m at R/2 and leaves with a speed of 400m/s. what is the angular speed of the disk right after? (omega) Homework Equations conservation of angular momentum Inertia for a disk The Attempt at...
  2. Q

    Is Fusion possible at the accretion disk of a Black Hole?

    So if we have a supermassive black hole or a regular black hole with gas swirling around it. Can this gas get hot enough to fuse with other gas molecules around it? It seems like there would be enough energy to do this, maybe not. This question seems non-trivial and I think it needs some...
  3. K

    Angular momentum of disk & clay?

    Homework Statement A rotating uniform-density disk of radius 0.7 m is mounted in the vertical plane. The axle is held up by supports that are not shown, and the disk is free to rotate on the nearly frictionless axle. The disk has mass 3.6 kg. A lump of clay with mass 0.4 kg falls and sticks...
  4. M

    Calc Volume of Disk - Rotate Region Bounded by y=1+secx, y=3 About y=1

    Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified line. y= 1 + secx, y=3, about y=1 Set up: 1-1+secx= secx 1-3= -2 A(x)= \pi(secx)^2\,-\,\pi(-2)^2 =\pi(sec^2 x - 4)...
  5. J

    DOS stands for Disk Operating System. Why is it named so?

    DOS stands for Disk Operating System. Why is it named so? Does the 'system' drive 'disk', or the 'system' is operated using some 'disk'? I know I have it right but it could help you to understand what I'm trying to ask. Please let me know. Thanks.
  6. T

    Disk moment of inertia example.

    A disk, cylinder shaped, of mass m and radius r is initially motionless on an ice rink. It has a massless string wound around it which you pull with a constant force F. After your hand has moved a distance d. How far has the c.m. of the disk moved? If someone could show me how I could do this...
  7. H

    Solid Shape Volume by Disk Method Problem

    Homework Statement The base of a certain solid is an equilateral triangle of side a, with one vertex at the origin and an altitude along the x-axis. Each plane perpendicular to the x-axis intersects the solid in a square cross section with one side in the base of the solid. Find the volume...
  8. K

    Torque friction on a rotating disk

    A uniform horizontal disk of mass M and radius R is rotating about its vertical axis with an angular velocity \omega. When it is placed on a horizontal surface, the coefficient of kinetic friction between the disk and the surface is \mu_k.Find a)the torque \tau exerted by the force of friction...
  9. K

    Potential Energy of a solid sphere and a thin disk

    A solid sphere with radius r is placed on top of a thin disk with radius R. The contact point is the center of the disk. Both objects are uniform and have the same mass M. Calculate the gravitational potential energy of the system. Take the potential energy to be zero when the sphere and the...
  10. C

    Period of oscillations of the disk

    Homework Statement A circular disk of radius R and uniform density is free to pivot about a fixed point P on its circumference. Calculate the period of oscillations of the disk, in the plane of Figure I, when it is displaced by a small angle about its pivot and released. Homework...
  11. P

    Forces on a Solid Disk: Determining F3

    Homework Statement Three forces of F1, F2, and F3 are applied to a solid disk with a mass of 3.6 kg and radius of 2.9 meters. F1 is directly above the center of the disk with a magnitude of 47 Newtons directed in the positive x direction, F2 is directly to the right of the center and has a...
  12. A

    The Volume of an Auxiliary Fuel Tank for a Helicopter?

    I think I did this right but I want to make sure since it is an extra credit problem and I could use the points. If I did something incorrect, I don't want an answer, just point me in the right direction so I can work it out myself. You are designing an auxiliary fuel tank that will fit under...
  13. A

    What is the Angular Velocity of Two Combined Disks?

    Homework Statement A disc off a mass m1 is spinning freely at omega1(w1). A second disk of the same radius but smaller mass m2=m1/4 is dropped onto the first , and it sticks. What is the angular velocity of the two disks The Attempt at a Solution I honestly have no idea
  14. Z

    Angular speed of a disk, given a force

    Homework Statement A uniform-density 7 kg disk of radius 0.27 m is mounted on a nearly frictionless axle. Initially it is not spinning. A string is wrapped tightly around the disk, and you pull on the string with a constant force of 45 N through a distance of 0.9 m. Now what is the angular...
  15. JJBladester

    Determine normal force and angular acceleration of disk

    Homework Statement A 10kg disk contacts an inclined surface. A 11Nm couple M is applied. The coefficient of friciton is 0.4. Determine the normal force at point D, the angular acceleration \alpha , and the force of the rod C. Answers: N=115.9 Newtons \alpha =2.25rad/s2 C=77.19 Newtons...
  16. V

    Newton's 2nd Law - Rotation, Torque, Disk

    Homework Statement Homework Equations Newton's 2nd Law F = ma Torque Equation τ = Iα The Attempt at a Solution Well I know I have to write separate equations for the masses and tensions so I got this: T1 - m1g = m1a T2 - m2g = -m2a -----> (negative because acceleration...
  17. W

    Angular momentum: disk with point mass on the edge

    Hi all, I'm treating a problem concerning a disk containing an additional point mass on the edge. The disk is moving (rotating and translating) relative to another fixed point, meanwhile it's spinning about its axes of symmetry. I'd like to determine the instantaneous angular momentum about...
  18. F

    CD Rotation Speeds & Acceleration: Analysis of a 12cm Disk

    Unlike the older vinal records which rotated at a constant ω of 33.3 rotations per minute (rpm), compact disks vary their rotation speed during the playing period. A certain CD has a diameter of 12cm and a playing time of 77 minutes. When the music starts, the CD is rotating at 480 rpm. At the...
  19. R

    Find the acceleration of the disk and the force of friction

    Homework Statement In the figure, a string is used to pull a disk of radius 18 cm and mass 9.3 kg. If the incline is 37° and the tension in the string is 20 Newtons find the acceleration of the disk and the force of friction on it. Homework Equations T=I(alpha) The Attempt at a...
  20. A

    Conservation of Angular Momentum of uniform disk

    Homework Statement A uniform disk turns at 8.6 rev/s around a frictionless spindle. A nonrotating rod, of the same mass as the disk and length equal to the disk's diameter, is dropped onto the freely spinning disk, see the figure. They then turn together around the spindle with their centers...
  21. F

    Potential of uniformly charged disk off axis

    Homework Statement As per Griffiths 3.21, I am given the on axis potential a distance r from a uniformly charged disk of radius R as a function of \sigma. Using this and the general solution for laplace's equation in spherical coordinates with azimuthal symmetry, calculate the first three...
  22. J

    Hyperbolic disk centrifugal stress calculation

    Please help - I am trying to figure out the stress in a hyperbolic disk rotating at some RPM. The best equations I could find (and example) is from the book "advanced Strength of Materials" by J. P. Den Hartog. Google books shows page 62 with these formulas: Thickness (t) = ti/(r^{q}) where...
  23. M

    Understanding the Airy Disk Equation: Lambda in Medium or Vacuum?

    hi the airy disk equation is d= 1.22 lambda / NA my question is: lambda is the wavelength in medium or in vacuum? thanks in advance
  24. V

    Sperical coords: Position vector of spinning disk.

    I posted this in the Intro physics sections, but then realized that spherical coords might be a bit complex for introductory physics. This has been bothering my head for a couple days now. Any help is appreciated. Given: A wheel of radius R rotates with an angular velocity. The wheel lies in...
  25. K

    Power produced by a rotation disk

    how do i calculate the power produced by a rotating disc? for example given that the constant angular velocity is 30rad/s, diameter of disc is 0.5m, mass is 15kg. or do u need more data to calculate the power? if yes, what data do u need?
  26. R

    Show that the given function maps the open unit disk into the upper half plane

    Homework Statement 4. Let w = f(z) = i(\frac{1-z}{1+z}). Show that f maps the open unit disk {z \in C | z < 1} into the upper half-plane {w\in C|Im(w) >0}, and maps the unit circle {z\in C||z|=1} to the real line. Homework Equations I was given this hint: "set w=i(\frac{1-z}{1+z}) and...
  27. T

    Thermal expansion of a metal round disk with hole in the middle

    This is my first post on this forum because I have a question that I cannot seem to answer myself. At my working place we have a machine where a metal conveyor belt is running through a section of the machine where the temperature is constant at 320 degrees Celcius. On this conveyor belt are...
  28. L

    Dynamics rotating disk, solve for r and theta magnitudes

    Homework Statement A screen clipping of the problem is here: http://img529.imageshack.us/img529/1738/dynamicsquestion2.jpg We have a circular disk that roates about its center, 0, with a constant angular velocity \omega (\omega = \dot{\theta}. The disk carries two spring-loaded plungers...
  29. M

    Show Poincare Disk is incidence geometry

    Homework Statement I have to show that the Poincare disk satisfies the incidence axiom that any line contains at least two points. Homework Equations There are two kinds of lines on the Poincare disk. I've found 2 points for the first kind, which are straight lines going through the...
  30. X

    Finding Volume of Rotated Solid: Disk Method

    Homework Statement Consider the solid obtained by rotating the region bounded by the given curves about y=10 Find the volume V of this solid using DISK METHOD Homework Equations y=5e^-x, y=5, x=4 The Attempt at a Solution setting up the picture easy. but I'm having...
  31. Y

    Normal derivative of Green's function on a disk.

    For circular region, why is \frac{\partial}{\partial n}G(r,\theta,r_0,\phi)= \frac{\partial}{\partial r_0}G(r,\theta,r_0,\phi) ? Where \; \hat{n} \: is the outward unit normal of C_R. Let circular region D_R with radius R \hbox { and possitive oriented boundary }\; C_R. Let u(r_0,\theta) be...
  32. V

    Optics: radius of a central disk of light

    Homework Statement A telescope objective is 12cm in diameter and has a focal length of 150cm. Light of mean wavelength 550nm from a distant star enters the scope as a nearly collimated beam. compute the radius of the central disk of light forming the image of the star on the focal plane of...
  33. S

    Nutating disk engine perspectives

    Recently there was information that military is developing a nutating disk engine http://en.wikipedia.org/wiki/Nutating_disc_engine" which, as they hope, will have higher power density, than reciprocating engine.Also some people say,that this is low friction design. Does anyone know what is...
  34. D

    Accretion Disk Density & Fusion: What You Need to Know

    Can an accretion disk get dense enough to start fusion? How dense does something have to be in order to start fusion? Does it depend on the material? is there a way of measuring the density of accretion disks?
  35. B

    Perfectly Inelastic Disk and Stick Collision- Angular Speed

    I think I'm not understanding something about this problem. Can someone help me out? Homework Statement A 2.0 kg disk traveling a 3.0 m/s strikes a 1.0 kg stick of length 4.0 m that is lying flat on nearly frictionless ice. The disk strikes the endpoint of the stick, at a distance r = 2.0 m...
  36. T

    Electron and Uniformly Charged Disk

    Homework Statement An electron (e) is to be released from rest on the central axis of a uniformly charged disk of radius R. The surface charge density on the disk is +3.50 µC/m2. (a) What is the magnitude of the electron's initial acceleration if it is released at a...
  37. F

    Prove That Charge Distributes Uniformly on a Disk Conductor

    I heard it's quite hard to prove that electric charge is distributed uniformly on a disk conductor. Can you point me to some resources online on the subject?
  38. S

    Spiral and Disk Galaxies are controlled by single parameter. What and How?

    This is a significant discovery that something is fundamentally controlling and ordering the properties of spiral and disk gaseous galaxies. Elliptical galaxies have no gas and no star formation. The question is not only what but how is the unknown parameter controlling spiral and disk galaxy...
  39. S

    Moment of Inertia for a Disk with Hole

    Homework Statement A uniform circular disk has radius 36 cm and mass 350 g and its center is at the origin. Then a circular hole of radius 7.2 cm is cut out of it. The center of the hole is a distance 10.8 cm from the center of the disk. Find the moment of inertia of the modified disk about...
  40. P

    How Do You Calculate the Moment of Inertia for a Disk and Block System?

    Homework Statement A uniform disk of mass Mdisk = 4.9 kg and radius R = 0.2 m has a small block of mass mblock = 2 kg on its rim. It rotates about an axis a distance d = 0.17 m from its center intersecting the disk along the radius on which the block is situated. a) What is the moment of...
  41. M

    How Can We Calculate the Radius of Gyration for a Rotating Disk?

    hello imagine a disk rotating by an axis that passes through the center of the disk how can we find the analogue of a mass rotating by an axis? I mean, how can we lump the whole mass of the wheel to a point? how much will be the distance of this point from the axis? for example to...
  42. A

    Velocity and Acceleration on a Rotating Disk?

    Homework Statement If you are standing on a rotating disk which is rotating at a constant angular velocity and you walk with a speed v along a straight radial line, then what are you velocity and acceleration? Homework Equations The Attempt at a Solution I just wanted to check if...
  43. F

    The mystery of the tangent and the radius fluid in spiral pipe on rotating disk

    Here's something simple but also a bit puzzling, let me know if you have any ideas... For clarity, I'll describe three cases before asking the final question (skip ahead if you like). 1. Mounted on a disk are two curved fences, just a few centimetres apart from each other. Between the fences...
  44. G

    What Happens to Angular Speed When Moment of Inertia Increases?

    A large flat disk with moment of inertia I is spinning with angular speed 18 rad/s a small object lands on the disk and changes the moment of inertia to 1.5I what is the new speed? i used L=I\omega to give me 18*1.5=27 rad/s i used this because L is the angular momentum of the disk and...
  45. Y

    Question about Laplace(Potential) equation of disk.

    Laplace equation: \frac{R''}{R} + \frac{1}{r}\frac{R'}{R} + \frac{1}{r^2}\frac{\Theta''}{\Theta} =0 Which give: r^2\frac{R''}{R} + r\frac{R'}{R} - \lambda R =0 \;and\; \Theta '' + \lambda \Theta =0 \theta \;is\; 2\pi \;periodic\; \Rightarrow\; \Theta \;is\; 2\pi \;periodic\...
  46. T

    Speed of Point on Rim of 50.0 g Disk with 8.00 cm Diameter

    Homework Statement A thin, 50.0 g disk with a diameter of 8.00 cm rotates about an axis through its center with 0.190 J of kinetic energy. What is the speed of a point on the rim?Homework Equations C = \frac{1}{2}MR^2 K_{rot}=\frac{1}{2}I\omega^2The Attempt at a Solution Since the formula for...
  47. M

    What is the maximum angular speed of a twisted disk?

    Homework Statement A thin metal disk of mass m=4.50 g and radius R=2.70 cm is attached at its center to a long fiber. When the disk is turned from the relaxed state through a small angle theta, the torque exerted by the fiber on the disk is proportional to theta. Suppose the disk is twisted...
  48. J

    Faraday's Disk Dynamo: why is there an emf?

    Consider a rotating disk on a uniform magnetic field. Faraday's law states that \epsilon = - \frac{d\phi}{dt} In this situation, \vec B is constant and the area of the disk is constant. Hence, the magnetic flux is constant and there should be no emf. What am I missing?
  49. A

    Two masses hanging from a disk

    Homework Statement A circular disk has two masses acting on it, m1=10g, m2=50g. The forces caused by these masses are 4.5cm (F1) and 6.8cm (F2) away from the axis of rotation (center). The angles are 130 degrees (F1, and on outer side away from center) and 98 degrees (F2, also on outer edge...
  50. D

    Induced Current Density On Disk Due to Changing Magnetic Field

    Homework Statement A very thin conducting disc of radius a and conductivity \sigma lies in the x-y plane with the origin at its center. A spatially uniform induction is present and given by B=B_0 cos\(\omega t \)\hat{z}. Find the induced current density \vec{J} in the disc. Homework...
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