bodies Definition and 501 Threads

I've seen much mention in websites of matt black surfaces being better emitters of infra red than shiny silver ones so if a matt black and shiny silver surface are heated to about 100 deg C the black one will cool down more quickly as a result of this! Doesn't Wien's law state that the amount of...

whenever 2 bodies are in contact , why do they exert force normal to each other on each other , i mean the normal force .

This question concerns a paradox I've come up with in GR. If somebody could tell me where it breaks down, I'd be much obliged. Thank you! Assume there is spaceship A hovering above a black hole, and spaceship B further away from a black hole The black hole, A, and B are all lined up. (The...

Homework Statement http://www.hdimage.org/images/bgkkpt63ckx96gu3xgh.jpg Homework Equations aA = aA/B + aB VA = VA/B + VB The Attempt at a Solution After staring at this question for some time, I finally had a go and got an answer of 1.25 rad/s, which is incorrect. I am totally...

Homework Statement On a leveled base is a plank with a mass M = 2 kg, on the plank is a weight with a mass m = 1 kg. What limit must the force exceed, when we pull the plank in a horizontal direction for the weight to slip from the plank? Ratio of friction between the plank and the base is...

Homework Statement Block A has mass m = 4.0 kg, and block B has mass m= 2.0 kg. The coefficient of kinetic friction between block B and the horizontal plane is 0.50. The inclined plane is frictionless at the angle 30 degrees and Block A sits on it. The pulley serves only to change the...

What is meant by total negative energy associated with bound bodies like planets. and also total energy of the hydrogen atom is negative. I wonder how it could be? Because I believe whatever negative energy may be, It must only be associated with bound systems, and I don't think that an isolated...

Stupid question, but I am no Einstein. So why do all the bodies have it? Does enegry also have it? What's it caused of? Thanks in advance, fawk3s

Homework Statement A wrecking ball is hanging at rest from a crane when suddenly the cable breaks. The time it takes for the ball to fall halfway to the ground is 1.31sex. Find the time it takes for the ball to fall from rest all the way to the ground. I think the formula to use is...

The velocity of a diver just before hitting the water is -10.2m/s, where the minus sign indicated that her motion is directly downward. What is her displacement during the last 1.10sec of the dive? I tried to use dthe x=1/2(Vinitial + Vfinal)t=40.8 but it's wrong, what am i doing wrong??

The Einstein field equation for gravity uses the stress-energy tensor, rather than just mass, to determine the gravitational force acting between two bodies. When spacetime curvature is small and relative velocities are much less than the speed of light, this force is well-approximated by...

I just want to get my head straight on something with regards to relativity and gravity - I think it's a simple question (or rather has a simple answer!) so there's no trick agenda here. If I have two bodies orbiting each other in deep space - far enough out for other gravitational forces to...

Hi all, I was bored a little while ago, and somehow started thinking about the Big bang and all that fun stuff. I once heard it said that some of the galaxies near the end of the universe are at close to light speed. Now I'm not here to dispute that (would be nice if it were true though) but...

Homework Statement A cord is wrapped around the rim of a solid uniform wheel 0.250 m in radius and of mass 9.20 kg. A steady horizontal pull of 40.0 N to the right is exerted on the cord, pulling it off tangentially from the wheel. The wheel is mounted on frictionless bearings on a...

Hi All, I don't know whether this question makes any sense or not anyhow i will ask. For example, consider a ball which is attached at the end of the string and let us assume that this ball rotates in the uniform circular motion. Then the reason it rotates in uniform circualar motion is...

Homework Statement A block of material of mass m and specific heat c falls from height h and reaches speed v just before striking the ground. Its temperature is measured immediately after it strikes the ground. If we ignore any change in temperature owing to interaction with the air, the...

Homework Statement okay, I know it says be descriptive and all, but I'll present a watered down problem with some insignificant data already calculated by me. my problem is to understand the logic behind the solution, I know the solution, I simply think my textbook is... false. here goes...

Homework Statement If an object falls five meters during the first interval of time, what is the total distance fallen at the end of the second interval of time? (Galileo's Theory of falling bodies) Homework Equations The Attempt at a Solution I know that at successive intervals of...

If an object falls five meters during the first interval of time, what is the total distance fallen at the end of the second interval of time? (Galileo's Theory of falling bodies) I know that at successive intervals of time the distance fallen is proportional to the odd numbers. So I suspect...

What will be the Gravitaional force between two bodies when the distance between them is zero e.g., If we place a ring around a sphere, the center of gravity of the two bodies coincide and thus the distance of separation is zero. F = G m1m2\d2 d = 0 ,F = Infinity

I have been reading about Acceleration Due To Gravity. All sources including Fundamentals Of Physics By Resnik say that ' Acceleration due to gravity does not depend on the object's properties like mass , density , shape etc '. The magnitude of 'g' is 9.8 m/s^2 for all bodies ? But I can not...

I have had this question for a very long time. Never got a convincing answer Every Heavenly body rotates about its axis. The sun, the planets, the galaxies, every heavenly body why is it so? what makes the rotate? ps:It is very likely that this question would be a repetition. If it is...

Homework Statement 2 bodies move towars each other M1 WITH Velocity V1 and M2 with velocity V2 ,on a frictionless surface with a spring between them(attached to M1),what will be the maximum contraction(I mean You know, shrink or W\E)? Homework Equations reduced mass...

I'd like to expand on the example Dweirdo set in his thread and ask a few different questions. I didn't want to hijack his thread as I thought it would keep info more organised if I separated the discussion. So, let's take the example that we have a black hole and two observers, one (A) far...

Homework Statement "Knowing that crank AB has a constant angular velocity of 160rpm counterclockwise, determine and plot, for values of \theta from 0 to 360 degrees, (a) the angular velocity and angular acceleration of rod BD, (b) the velocity and acceleration of collar D...

Hi How would I show that the centre of mass of two point particles, one of mass m1 and the other m2, when released from rest from infinite simultaneously, stays in the same place? I feel this is a very simple question, I just can't seem to get it right. Everything I've tried still involves...

Homework Statement A wrecking ball weighing 4800N is supported by a uniform boom of wieght 3600N. A support cable runs from the top of the boom to the tractor. the angle between the support cable and the horizontal is 32degrees and the angle between the boom and the horizon is 48degrees...

Homework Statement If the system is released from rest, determine the speeds of both masses after B has moved 1m. Neglect friction and the masses of the pulleys. http://img14.imageshack.us/img14/6321/fbd.jpg The Attempt at a Solution I have drawn up the free body diagram for both...

If both bodies are in motion and come into contact, say a ring sliding on a block in motion as well. The speed of the ring (RPM) and the speed of the block in motion would both change once the bodies come into contact. Is there a way of calculating what the speeds of both bodies would be...

Homework Statement Consider 2 magnetic masses, m1 and m2; these 2 repel each other for a distance s with force f (relative to each other)...which applies from m1 to m2. Predict final velocity of m1 and m2. Assume final distance to be v1 and v2 Assume the 2 masses at rest initially...

why do bodies at rest weight more than zero? here is the bull thing... now I am sitting on my chair and i know Earth exerts a force on me which is called my weight. by definition w=mg I DO NOT have any acceleration g or anything else. let me prove a = dv/dt my speed is zero v = 0, coz...

I'm currently writing a vehicle simulator and have constructed a chassis out of physical node bodies that are connected as in the screenshot below. I am trying to work out the normal force at each of the green circles such that if it were suspended by each of the four nodes, the summation of the...

(i) how you solved this problem, An object of mass 10 kg is dropped from a great height. (a) If the object is subjected to air resistance equivalent to 10 times the instantaneous velocity, find the velocity. (b) How far does the object drop after 5 sec? (ii) what you got as a solution...

I am having trouble on this problem. An object of mass 10 kg is dropped from a great height. (a) If the object is subjected to air resistance equivalent to 10 times the instantaneous velocity, find the velocity. (b) How far does the object drop after 5 sec? Ok so I thought the equation...

Hi there, I have to solve the following problem: A semi-infinite body x<0 has thermal conductivity K_1 , density \rho_1 , and specific heat C_1. It is initially at temperature T_0. At time t=0, it is placed in thermal contact with the semi-infinite body x>0, which has parameters K_2 , \rho_2...

Hello all. I'm trying to find the equation for combined Center of Gravity (CoG) when you combine two objects with different weight. I know how to find the centroid, which is what the CoG would be if both objects were the same weight. But what about two objects with different weight...

Say the gravitational force between two points is 80 N. The two points start off stationary. What do I do to find how those two objects would accelerate closer together? I'm trying to write a simple program that calculates the gravitational force between two objects and pulls them together, but...

I posed this question to my teacher: I have a 2 kg object and it sits at rest on the floor. The force is mass * acceleration, so it's about 20 N. Now I drop the ball from, say, 20 feet above the ground. Same mass, same acceleration, so it has the same force, 20 N; but we know the object hits...

Homework Statement A 2-kg block falls from rest a vertical distance of 0.75 meters above the top of a spring. The block lands on top of the spring compressing it 0.35 meters from its equlibrium position. a) What is the gravitational potential energy of the 2-kg mass just before it is...

It's often said there are no rigid bodies in relativity. Is the notion of "angle" primary or derived in relativity? Does "angle" require rigid bodies, at least "locally"? For example, to use light rays to measure the metric, do we need mirrors which are "rigid"?

Homework Statement One stellar mass is defined as the mass of our sun (1Ms = 1.99 x 1030 kg). ONe astronomical unit is defined as the length of Earth's semi-major axis (1AU = 1.49 x 1011 m). The star Epsilon Eridani in the constellation Eridanus has a planet (discovered in 2000) orbiting it...

Homework Statement A hollow cylindrical shell with mass M = 100 g and radius R = 5 cm rolls without slipping down an inclined plane making an angle \alpha = 30° with the horizontal. (a) If the initial speed of the shell is zero, what will be the speed of its center of (c) Calculate...

Hi.I have some confusion on this question ...here is the question 1.A(n) 2.6 kg object moving with a speed of 7.9 m/s collides with a(n) 3 kg object mov- ing with a velocity of 7.4 m/s in a direction 56.1768◦ from the initial direction of motion of the 2.6 kg object.What is the speed of...

Homework Statement The Stardust spacecraft was designed to visit a comet and bring samples of its material back to the earth. The craft is 1.7 m across and has a mass of 385 kg. In January 2004, from a distance of 237 km, it took the photograph of the nucleus of comet Wild2, shown in the...

Homework Statement A ball is thrown from top of a 25m tall building. The balls initail speed is 12m/s. At the same instant a person is running on the ground at the distance of 31m from the building. What must be the avg speed of the person if he is to catch the ball at the bottem of the...

Homework Statement Two bodies A and B of mass m_1 and m_2 are connected via a spring of natural longitud l_0 and elastic constant k. Both bodies are free of net force until at an instant t_i something applies a constant force F to the body A, in the direction of B. (see the diagram)...

Homework Statement A ball is thrown straight upward and rises to a maximum height of 18 m above its launch point. At what height above its launch point has the speed of the ball decreased to one-half of its initial value? Homework Equations i don't know. The Attempt at a Solution...

I have a couple problems that I can't seem to get. The first I'm really close, I can tell, because my professor did one that was similar in class. The answer the book gives is 250 lbs, I'm coming up with 225. The second I think is similar to another problem he did in class but I'm not...

What happens if we apply on B a force bigger than the static friction with the floor and also bigger than the static friction with the upper body A, but smaller than their sum? Will B move? what about A?

<crackpot link removed> So what's up with them?