What is Disk: Definition and 816 Discussions

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  1. J

    Iron rod - will flux link with disk above it

    If an aluminium disk is placed above a COMPLETELY vertical current carrying iron rod will any flux link with the aluminium disk... Firstly, does it matter if the current is AC or DC. I presumed not as the only difference is that the magnetic field will vary in one case and stay constant in...
  2. J

    Statics Problem: hanging disk, tensions etc.

    Homework Statement The circular plate has a weight W and a center of gravity at its center. If it is supported vy three vertical cords tied to its edge, determine the largest distance d from the center to where any vertical force P can be applied so as not to cause the force in anyone of the...
  3. J

    Compact disk angular acceleration

    Homework Statement A compact disc speeds from rest to 5200 rpms in 620 rad. Diameter is 5.0cm -how many revolutions did it make in this time -what is the angular acceleration in rad/s^2 -how long does ti take to reach this speed Homework Equations The Attempt at a Solution i was able to find...
  4. J

    Accretion disk around galaxy NGC 4261

    Hello, When you look at the accretion disk around NGC 4261 (see here), you can read that the dark, dusty disk represents a cold outer region which extends inwards to an ultra-hot accretion disk with a few hundred million miles from the suspected black hole. So, from the outside, you have...
  5. N

    What determines the speed of two balls on a rotating disk?

    Homework Statement Homework Equations I=mr^{2} L=ωI ω=\frac{L}{I} The Attempt at a Solution I thought that since the moment of inertia was larger for the ball on the outside its angular speed would be slower. So then it would take longer to hit the wall.
  6. G

    Magnitude and Direction of a Magnetic Field at the Circumference of a Disk

    Homework Statement A very thin disk of non-conducting material initially holds a charge QO = +5 μC that decreases with time t as Q(t) = QO e-t/τ where τ = 10 seconds. If the disk has a radius of 0.10 m, what is the magnitude and direction of the magnetic field at the circumference of...
  7. R

    Moment Of Inertia Of A Semi-Circular Disk?

    Homework Statement http://dl.dropbox.com/u/630750/Screen%20Shot%202012-04-26%20at%2010.03.36.png Homework Equations The Attempt at a Solution http://dl.dropbox.com/u/630750/Photo%2026-04-2012%2010%2001%2034.jpg I know this is wrong but I can't really see why, can anybody...
  8. R

    How Much Sooner Does a Box Reach the Bottom of an Incline Compared to a Disk?

    A disk and a box of equal mass are released from the top of two inclines both of which are a height h above the ground and make an angle θ to the horizontal. Let the radius of the disk be R. How much sooner does the box reach the bottom of the incline than the disk? Express your answer in terms...
  9. C

    Evaluating Double Integrals of Odd and Even Functions on a Disk

    Homework Statement Suppose f : ℝ→ℝ and g : ℝ →ℝ are continuous. Suppose that f is odd and g is even. Define h(x,y) : f(x)*g(y). Let D be a disk centered at the origin in the plane. What is ∫∫h(x,y)dA? D The Attempt at a Solution I know there's probably a trick to it. Is it 0...
  10. L

    Moment of inertia of disk about off centre axis

    Homework Statement Find the moment of inertia of a uniform disk of mass m and radius r about an axis normal to the disk, through a point x from the centre. Homework Equations The Attempt at a Solution Let ρ be the density. I=ρ∫r^2 dA=ρ∫∫r^3 dr dθ in polar coordinates. However I...
  11. D

    Disk rolling down a hill with no sliping

    A disk with mass m and radius R is rolling down a hill with no slipping, until it reaches a wall and then stops: I want to write a set of equations describing the position cordinates x and y of the disk's center of mass (point A) and the cordinates for point B. mgsin(theta)=ma ->...
  12. T

    Electromagnet stick is the key to build a flying disk

    The electromagnet stick always head N/s, no matter how fast the rotation of the shell of the disk is, you just need to control the input voltage of it, and it will not get heavy if the Magnetic stronger. I think the input higher voltage can make it head with power and hard to change the...
  13. G

    Poincare disk model. Circle question.

    Homework Statement Use the Poincare (disk) model to show that in the hyperbolic plane, there exists two points A, B lying on the same side S of a line l such that no circle through A and B lies entirely within S. Homework Equations The hint was to use this proposition: A P-circle is a...
  14. N

    Rotational motion of a spinning disk

    Homework Statement A spinning disk is rotating at a rate of 30 rad/s in the counterclockwise direction. The disk is slowing down at a rate of 6 rad/s2. Find the angle through which the disk has turned after 3 s in radians, degrees, and revolutions. Homework Equations θ=θi + ωi*t + αt^2...
  15. D

    Inertia of a solid vertical disk about it's diameter

    Homework Statement Derive the moment of inertia of a solid, uniform density, disk rotating about a diameter using vertical rods. Diagram: http://i.imgur.com/TQIjz.png Only the radius of the circle and the inertia of a thin rod is given Homework Equations Inertia of thin vertical rod = m*r^2...
  16. R

    Steady-State Temperature Distribution of a circular disk

    Homework Statement A circular disc of radius a is heated in such a way that its perimeter r=a has a steady temperature distribution A+B \cos ^2 \phi where r and \phi are plane polar coordiantes and A and B are constants. Find the temperature T(\rho, \phi) everywhere in the region \rho < a 2...
  17. A

    Charge density for a disk moving at constant velocity

    Problem Statement: I'm having some trouble understanding how to write charge densities using delta functions, particularly when they involve geometries other than Cartesian. So I have a disk moving with velocity v (along the z-axis) that has total charge Q, and I'm trying to write ρ(x,t) so that...
  18. Drakkith

    How to Calculate Intensity in Airy Disk from a Point Source?

    I'm trying to figure out the intensity of light in different sections of a 2d airy disk from a point source, but I'm not sure how to calculate it. Does anyone have any good sources?
  19. fluidistic

    Charge distribution of a uniformly charged disk

    Homework Statement The problem can be found in Jackson's book, I think in chapter 1 problem 3 or something like this. I must determine the charge distribution of a uniformly charged disk of radius R in spherical coordinates (I've done it in cylindrical coordinates and had no problem). The...
  20. X

    Calculating Average Tangential Stress for Non-Uniform Rotating Disk

    Assumed a disk loaded with external pressure Po, internal Pressure Pi and rotating at the speed ω. I'm sure that average tangential stress for uniform thickness rotating disk can be calculated using equation below : σ avg = (PiRi/Ro-Ri) - (PoRo/Ro-Ri) + (ρω^2) / 3(Ro^2+RoRi+Ri^2) Ro = outer...
  21. S

    The Electric Field of a Uniformly Charged Disk

    Homework Statement A disk of radius R has a uniform surface charge density σ. Calculate the electric field at a point P that lies along the central perpendicular axis of the disk and a distance x from the center of the disk. Homework Equations Electric field due to a continuous...
  22. binbagsss

    Electric field exerted at P due to a non-conducting disk

    A non-conducting disk has radius 1.25cm and charge 6.55nc. What is the electric field (magnitude) experienced at a point P - where p = 2cm and is on the x-axis. The disk's centre is placed at the origin. I approached this problem using the general formula derived: k/2Σσ [1 -...
  23. I

    How much rotational kinetic energy does the disk have ?

    A string is wrapped around a disk of mass 2.1 kg (it's density doesn't have to be uniform). From rest, you pull the string with a constant force of 9 N. At this instant, the center of mass has moved 0.11 m, and your hand has moved 0.28 m. 1. At this instant, how much rotational kinetic...
  24. C

    Calculating Rotational Energy of Disk After Forces Applied

    Homework Statement A uniform disk with mass m = 9.32 kg and radius R = 1.37 m lies in the x-y plane and centered at the origin. Three forces act in the +y-direction on the disk: 1) a force 340 N at the edge of the disk on the +x-axis, 2) a force 340 N at the edge of the disk on the –y-axis...
  25. O

    How close is a 2D Gaussian to an Airy disk?

    So we were taking measurements for an experiment in our radio astronomy lab. For the first part of the experiment, we recorded the intensity of a far away point source ( the signal from a TV satellite was used for the point source ) detected by commercial satellite dish and receiver. When we...
  26. A

    Calculating the gravitational field due to a horizontal uniform thin disk

    Homework Statement Show that the gravitational field due to a horizontal uniform thin disc (thickness D, radius R and density r) at a distance h vertically above the centre of the disc has magnitude 2πGρd(1-h/(R2+h2)1/2) A pendulum clock in the centre of a large room is observed to keep...
  27. C

    Torque required to rotate a disk

    Homework Statement How much torque is required to rotate a disk or diameter 1.4cm, height 1cm, weight 12g? Homework Equations I think Iz = mr^2/2 Torque = force x distance The Attempt at a Solution Iz = 2.95 * 10^-7 I do not know where to go from here. Thank you.
  28. C

    How to decide the voltage for the piezoelectric disk on the droplet generator

    Now I am designing a piezoelectric droplet generator. The problem I am facing now is that the vibrational amplitude of the piezoelectric device is not sufficiently great. I do not know how to determine the voltage applied to the piezoelectric disk for my droplet generator. Can someone provide me...
  29. M

    Disk Brake Connections: Finding Torque & Bolt Amounts

    I'm trying to connect a disk from a brake to a shoulder using self locking screws but can't find a formula that would help me to calculate the torque these screws would be subjected to or how many bolts I would need. What do I need to do?
  30. D

    Mechanics Goldstein, chpt 1 exercise 11, Lagrangian of rolling disk

    Homework Statement I apologize if this is not the right place to put this. If it is not please redirect me for future reference. 11. Consider a uniform thin disk that rolls without slipping on a horizontal plane. A horizontal force is applied to the center of the disk and in a direction...
  31. I

    Volume of cathedral dome (Using volumes of revolution, disk method)

    Homework Statement A cathedral dome is designed with three semi circular supports of radius r so that each horiontal cross section is a regular hexagon. Show that the volume of the dome is r^3 * sqrt(3) an accompanying figure - http://imgur.com/3fSqh Homework Equations...
  32. G

    Finding an electric field on a disk using surface charge density

    Homework Statement A disk of radius 2.30 cm has a surface charge density of 5.22 μC/m2 on its upper face. What is the magnitude of the electric field produced by the disk at a point on its central axis at distance z = 11.2 cm from the disk? Homework Equations Formula for an electric...
  33. J

    Rectangular Disk with Circular Hole Period Question

    Homework Statement A circular disk with a rectangular hole has a radius of 0.620 m and mass of 0.470 kg. It is suspended by a point on its perimeter as shown in the figure. The moment of inertia about this point is I_p = 1.60E-1 kgm2. Its center of mass is located at a distance of s=0.120 m...
  34. B

    Stress calculations on a disk plate

    Hello, I am trying to determine the calculation to use to determine the force at which a disk plate will fail for the following set up. The disk is slid onto a metal bung for a roll, the disk is supported from the inside diameter for around 50mm. A force is then applied on the oppsite side...
  35. P

    What Is the Rotation Speed of a Disk After Being Tossed?

    How fast a disk is rotating? Please help me Im trying to attempt this problem, its not a assigned homework problem but it has 2 stars beside it(which means its one of the harder ones) in the book so I am trying to solve it but i don't even know how to begin and have a crack at it. I really...
  36. T

    What are the Dimensions of a 2.5' Hard Disk Drive?

    Hi there, does anyone knows the overall dimension for 2.5' hard disk drive?including all the components inside. who has the complete dimension? tq =)
  37. K

    Two points are on a disk that rotates about an axis perpendicular to the plane

    Two unequal masses m and 2m are attached to a thin bar of negligible mass that rotates about an axis perpendicular to the bar. When m is a distance 2d from the axis and 2m is a distance d from the axis, the moment of inertia of this combination is I. If the masses are now interchanged, the...
  38. G

    Is acceleration constant when a disk is rolling down a ramp?

    I don't understand when acceleration is constant and when it changes. What are some examples of situations where the acceleration is constant and when it's not? Is acceleration constant when a disk is rolling down a ramp?
  39. A

    Exponential disk. Rotation velocity

    Hello I have been modeling the rotation curves of galaxies. Can help in calculating the rotation velocity for a thin exponential disk. I use the method of Kent S. http://articles.adsabs.harvard.edu//full/1986AJ...91.1301K/0001310.000.html My implementation in C #...
  40. P

    What is the Angular Acceleration for a Rotating Computer Disk Drive?

    Homework Statement A computer disk drive is turned on starting from rest and has constant angular acceleration. If it took 0.690s for the drive to make its second complete revolution, how long did it take to make the first complete revolution? What is the angular acceleration?Homework Equations...
  41. S

    Rotational Mechanics Problem (Rotating solid wooden disk)

    I have the working for part d) but I don't understand certain parts, so my problems lie with part d), f) and g) Homework Statement 3. A solid wooden disk is suspended as shown: it has mass 7.70 kg and radius 0.219 m . It is rotated from rest about its vertical axis, reaching an angular...
  42. W

    Does a shrinking disk grow in the z-direction?

    This is not a homework question! I am observing that a thin, flat disk made from a material whose density is gradually increasing, shrinks in the radial direction (of course) but appears to grow very slightly in the z-direction. The change in density is supposed to be isotropic. Is growth...
  43. D

    Moment of inertia of a disk

    Homework Statement What is the moment of inertia of an 8 kg, 40 cm diameter disk for rotation through the edge of the disk? Homework Equations I = \frac{1}{2}MR^2 The Attempt at a Solution Inertia at the center of the disk would be I = \frac{1}{2}MR^2, right? I'm not sure what...
  44. I

    How can the E field for a disk be derived using Gauss's law?

    Homework Statement I came across an expression in the following pdf at the bottom of page two: http://iweb.tntech.edu/murdock/books/v4chap2.pdf Homework Equations The electric field for a disk: \vec{E} = \frac{\sigma}{2{\epsilon}_{0}} ( 1 - \frac{z}{\sqrt{{z}^{2} + {r}^{2}}}) Now logically...
  45. A

    Velocity of center of mass of spinning disk

    A solid uniform disk of mass 19.0 kg and radius 70.0 cm (.7 m) is at rest FLAT on a frictionless surface. A string is wrapped around the rim of the disk and a constant force of 35.0 N is applied to the string. The string does not slip on the rim. The string is being pulled. When the disk has...
  46. B

    Magnetization and torque in an ellipsoidal disk

    If I have an ellipsoidal disk, where the demagnetization constants Nd_{xx}>>Nd_{yy}>>Nd_{zz}. The disk lies on the y-z plane and easy axes are +z or -z. The energy of the system (just considering demag fields) will be U=Nd_{xx}sin^2\theta cos^2\phi + Nd_{yy}sin^2\theta...
  47. B

    What is the integral setup for finding probability within a disk?

    I'm taking a probability class where multivariate calculus was not a prerequisite, but some of it is coming up, I get the concept of, say integrating over a region, but get lost in some of the mechanics Here is the problem (I don't want a full solution): A point is uniformly distributed...
  48. A

    Physical pendulum made of a uniform disk

    Homework Statement A physical pendulum is made of a uniform disk of mass M and radius R suspended from a rod of negligible mass. The distance from the pivot to the center of the disk is l. What value of l makes the period a minimum? Homework Equations The Attempt at a Solution
  49. jegues

    Uniformly Polarized disk on a conducting plane (E-Field)

    Homework Statement A uniformly polarized dielectric disk surrounded by air is lying at a conducting plane, as shown in the figure. The polarization vector in the is, \vec{P} = P \hat{k}, the disk radius is a, and the thickness d. Calculate the electric field intensity vector along the...
  50. jegues

    Uniformly polarized disk on a conducting plane.

    Homework Statement A uniformly polarized dielectric disk surrounded by air is lying at a conducting plane, as shown in Fig. 2.36. The polarization vector in the disk is, \vec{P} = P\hat{k}, the disk radius is a, and the thickness d. Calculate the electric field intensity vector along disk...
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