Disc Definition and 397 Threads

Regarding electric field at the center of a uniformly charged disc? The electric filed at a distance x from the center of a uniformly charged disc of radius R,along the axis passing through the center is given by E = sigma/2e(1-x/rt(x^2+R^2)) where sigma is surface charge density and e is...

im struggling abit with this question. i have a formula but it doesn't really go with my question a brake disc has the following specification mean radius 0.16m force applied to each pad 5045N U = 0.35 brake disc rotational speed is 550rev/min work out its frictional torque work done...

I am trying to write a simulation program for a relatively complicated mechanical system. Parts of it will be strings wrapped around discs under tension - with the discs moving and rotating. So, I decided to figure out the basics, and am stuck. The situation is thus: An unstretchable...

Homework Statement A) a horizontal disc of diameter 12.0cm is spinning freely about a vertical axis through its centre at an angular speed of 72 revolutions per minute. a piece of putty of mass 5.0g drops onto and sticks to the disc at a distance of 4.0cm from the centre. The angular speed...

Homework Statement I need a quick sanity check here please. (Sorry, my alphas keep coming out as power signs, they're not!). To find the force to slow a spinning disc with known moment of inertia (0.0004kgm2) and known angular velocity (120pi rad/s) to a stop in 6s. Here, the...

1. Find the Moment of Inertia of a Quarter Disc which has mass M and radius R about the axis passing through the center (of original disc) and perpendicular to the plane. 2. The attempt at a solution I found the Moment of Inertia (I) of a disc about the axis passing through the center...

Homework Statement Given \epsilon > 0 , show that the unit disc contains finitely many dyadic squares whose total area exceeds \pi - \epsilon , and which intersect each other only along their boundaries. Homework Equations The Attempt at a Solution I've tried to solve this...

How far has the disk moved? Disk has .34m radius with a mass of 7.4. The angular acceleration about the center of mass is 100.2 rad/s2. So this is what i did: ang. disp= .5(ang. accel)*t^2 (x=.5(a)t^2 =>pretty much) I got my ang. disp to be 84.669 rad. Now i need to convert it to meters. The...

Homework Statement \D = \{(x,y) \in \mathbb{R}^2 | x^2 + y^2 \leq 1\} i.e. a disc or radius 1. Write down the pdf f_{xy} for a uniform distribution on the disc. Homework Equations The Attempt at a Solution f_{xy} = \frac{(x^2 + y^2)}{\pi} \mbox{for} x^2 + y^2 \leq 1 0...

Homework Statement \D = \{(x,y) \in \mathbb{R}^2 | x^2 + y^2 \leq 1\} i.e. a disc or radius 1. Write down the pdf f_{xy} for a uniform distribution on the disc. Homework Equations The Attempt at a Solution f_{xy} = \frac{(x^2 + y^2)}{\pi} \mbox{for} x^2 + y^2 0 \mbox{otherwise} as the...

Homework Statement This is a problem I found in my note. It says that from u xx(subscript) + u yy = 0, we can arrive at u rr + (1/r) u r + (1/r^2) u theta theta = 0 by using the transformation x = r cos theta, y = r sin theta, r = square root of (x^2+y^2), theta = arctan (y/x). The...

Hey Folks I have rather a silly doubt i guess... It goes like this Consider a disc rotating about a fixed axis with constant angular velocity. Which means it has no angular acceleration ie it must be 0. Now since Torque=(moment of inertia)*(angular acceleration). hence the torque acting on...

Homework Statement Find the power-series expansion about the given point for the function; find the largest disc in which the series is valid. f(z) = z^3 + 6z^2-4z-3 about z0=1. Homework Equations The Attempt at a Solution The series is fine. Since it's a polynomial, there are only three...

Homework Statement a disc drive at rest is powered up and accelerates according to alpha=alpha(i)sin(bt). this lasts for 1.66 seconds after which it no longer accelerates. alpha(i)=506 rad/s^2 b=1.89 radius of disc=3.9cm. After the disc is done spinning up what is the centripetal...

Homework Statement When powered up, a disk drive starts at rest and spins up with non-uniform acceleration. this lasts for 1.66 seconds after which it does not accelerate any more. how fast is it spinning at .87 seconds? alpha(i)=605 rad/s^2 B=1.89 Radius=2.03 cmHomework Equations...

hi there What is a Poincare' disc and why is the edges of disc represent infinity? thanks

Homework Statement I want to find a bijective function from [0,1] x [0,1] -> D, where D is the closed unit disc. Homework Equations The Attempt at a Solution I have been able to find two continuous surjective functions, but neither is injective. they are...

I understand that to find moment of force, we look at direction of force and perpendicular distance. In the diagram, O is the centre and pivot of the circular disc. Would the anticlockwise moment at A be (30N x 4m)? I'm not sure if this is true, cos the distance 4m is only AB. It does not...

Homework Statement 1. Find the volume of the solid generated by revolving the region bounded by the graphs of the equations about the indicated lines. y = \sqrt{x}, y = 0, x = 4 the line x = 62. Find the volume of the solid generated by revolving the region bounded by the graphs of the...

Can you show me a metric on the 2 dimensional disc so wild that no open subset can be embedded in R^3?

Hi, I am a little stuck on this question from a PPOD paper I am doing all help appreciated =) Homework Statement A solid circular disc of mass 6.6kg and radius 0.25m rotates about an axis which coincides with its diamter. Its angular acceleration is found to be 6.7rad/s. The axis of...

Why does a Frisbee delivered by a right handed thrower with a back hand release tend to roll to the left? or in general: Why does a flying disc tend to roll in the opposite direction that it is spinning? (see attached image)

hey kinda new to this and I know the rules say I am not allowed to be told how to do this but I am totally stumped and its to be handed in tomorrow. I've looked through everything and cannot find out how to do it anywhere I am starting to think there is a typo in the question paper :S show...

Homework Statement http://scitec.uwichill.edu.bb/cmp/online/P10D/Hunte/Electric%20fields_files/image122.jpg Find the Electric Field at Point P at height z over a uniformly charged disc of radius a with uniform charge Q. Homework Equations The Attempt at a Solution I'm looking...

What is the inner radius of an accretion disc? Is it simply the radius of the smallest possible orbit of a massive particle (the marginally stable radius), 6M ?

Homework Statement The planes x= ±a are charged to uniform surface density ±σ respectively. Find the charge and current densities in a frame moving with velocity (0,v,0) - [done] Find also the electromagnetic field in the moving frame by solving the problem in the moving frame...

Homework Statement The question actually asks for the equation for the magnetic field for the rotating disc; but all I'm after is the direction of the magnetic field. Homework Equations None were given; but I've been using: \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t}...

1. Tim of a mass of 50 kg is standing on a large spinning disc of a mass of 80kg and a diameter of 5m. Tim standing at the edge of the disc which is rotating at 25 rad/s. He then walks to the center of the disc. Calculate the new angular velocity of the disc. 2. IW=I'W' IdiskWdisk + ImitchWmitch...

Homework Statement A 750 gram grinding wheel 25.0 cm in diameter is in the shape of a uniform solid disc. When it is in use it turns at a constant 220 rpm about an axis perpendicular to its face through its center. When the power is switched off the wheel stops in 45.0 s with constant angular...

I spent a long time just trying to find the right equation and it was no surprise that I did not understand a variable of it. Homework Statement Why is it that a tower of identical disc magnets behaves differently (is stronger than?) a single magnet. Known: NO NUMBERS Each disk is...

Hi, I need to find an answer for the following question: What happens when you apply a tangential force instantenously to a disc laying on a frictionless surface? Does it rotate, translate or both? Here is an illustration for a better explanation...

Homework Statement Basically I've got a brake system which i have designed, and i need to calculate if the brake fluid will overheat if the vehicle brakes from its top speed to a halt, and if so at what speed (or how long after braking commences) they will overheat Brake force = 13000N...

Homework Statement The function is y = 2 - x. The region is bounded by x = 2 and x = 4. Calculate its volume by the shell method by rotating it by the x axis. The Attempt at a Solution This problem has been consuming my mind. I calculated it by the disc method and shell method but I...

Hello, I am working on a rough sketchup for a Mechanical Design Project involving a motorcycle brake. I am working on finding the Contact area of a brake pad on the rotor of a motorcycle. I have already found the torque and forces involved to actuate the pads against the rotor...

how to determine the torque of a rotating disc in order to find the power of motor? there is a rotating disc, and a ball will pass through and launched by the rotating disc. the initial speed is 20m/s, and i could determine the rpm from here. the information i have now: the disc diameter...

I am to design a sensor element that can detect a leakage through a thin metal disc (rupture disc) in a pipeline. Ideally, the metal disc closes the pipeline at the upstreaming side with certain pressure. Its downstream can be either open to atmosphere or close. When a higher pressure occurs...

The discs of all large galaxies show a "flattening" of their discs where the material at the outer edge of the discs rotate at the same rate as the material near the center of the galaxy. The explanation for this is that the galaxy must be embedded in a halo of invisible "dark" matter which, I...

I am trying to understand continuous and discontinuous. These are two assignments I have for a class. I am just looking for some feedback... Let A= {1/n : n is natural} Then, f(x)= (x , if x in A) (0 , if x not in A) This is discontinuous on A but continuous on A...

Homework Statement A cylinderical rod of length (l), and diameter (d) and evenly distributed mass (m) is oscillating harmonically (ie y(t) = Acos(wt)) with a driven frequency that makes the rod stable in the upright postion (ie inverted pendulum) A ring/disc of mass m' is fitted over the rod...

Homework Statement A thin disc of radius R carries a surface charge \sigma. It rotates with angular frequency \omega about the z axis, which is perpendicular to the disc and through its center. What is B along the z axis? Homework Equations General Biot-Savart law: B(x) =...

Hey - I am a bike mechanic with a large interrest in physics. I know that a larger disc brake rotor provides a greater braking effectiveness, but how can you mathmatically prove it by using physics formulas? And what formulas would be useD? Any ideas would be highly appriciated!

Hi! please help me! I am having a real problem this days about my free space on my local disc C. Sometimes when i turn on my computer i find that the free space on my local disc has diminished itself without that i have saved anything on it before . This is very serious because there is at...

I bought a computer from a store over a year ago and it came with a recovery disc for the OS. i know you can't use the disc on a different computer but can it be used on the same machine if the motherboard is changed out. it seems like it wouldn't since the motherboard and processor are what...

hi everyone. newbie here and i havea question that has to do with my personal experience. Today i jumped off a 50 foot cliff into deep water. the current was calm. i found this cliff at "great falls" virginia. me and a bunch of friends decided to jump off a cliff which was approxomity 50...

You stand on the edge of a large rotating disc. It rotates at a constant speed. You walk towards the centre of the disc. What do you experience? radius is decreasing, therefore inertia and linear velocity are decreasing. but angular acceleration will increase. i don't know if I'm right

Now we know Evo is ok ish i will tell of my latest, While cutting a seized inner bearing off a 60 mm shaft the cutting disc exploded and cut my finger to the bone, luckily i was wearing a a safety mask as a shard cut a grove in it, the last time i used a cutting disc i set my overalls on fire.

Homework Statement Hi all. I can't seem to understand how to apply Lenz' law to a disc rotating in a magnetic field that is perpendicular to the discs plane (see first page on PDF): http://www.pa.uky.edu/~latimer/phy232s08/lectures/phy232l31_4.pdf I can see that using the right-hand...

Consider a disc in the framework of special relativity. It's initially at rest in an inertial frame, and then you get it rotating in a way that respects the symmetry of the circle (e.g. by turning a thin rod through its center). There's no way that the acceleration of the different parts of the...

Homework Statement http://img372.imageshack.us/img372/4379/diagyx7.jpg A uniform disc has centre O,radius a and mass 2m. It is free to rotate in a vertical plane about a fixed horizontal axis through O. A particle of mass m is placed on the highest point of the rough edge of the disc and the...

I am slipping off my spinning disc-- Homework Statement I am taking a non calculus based physics class and have hit a wall with this one. I have a horizontal spinning disc with an Angular Acceleration of .25 rad/s^2 from rest. The disc has a radius of .05 m. A pebble is placed .025m from the...