Conservation of energy Definition and 1000 Threads

Homework Statement http://www.screencast.com/users/ntrinh3/folders/Jing/media/a4165a56-de0d-4a4a-a01e-49242fd505c4 Need help with question 13 Homework Equations Conservation of energy and momentum occurs in elastic collision The Attempt at a Solution Why would the block 2 have an...

I have a quick problem. A uniform hollow disk has two pieces of thin light wire wrapped around its outer rim and is supported from the ceiling (the figure ). Suddenly one of the wires breaks, and the remaining wire does not slip as the disk rolls down. Use energy conservation to find...

I'm not sure the question belongs to classical physics, I apologize in case it's a no. Imagine a train or any object following a straight line motion. Suppose there's no friction between the ground and the train, such that its motion would go on forever. Now suppose that the train emits...

Homework Statement A baseball is thrown from the roof of a building of height 21.2m with an initial velocity of magnitude 10.7 m/s and directed at an angle of 54.4 degrees above the horizontal. a. What is the speed of the ball just before it strikes the ground? Use energy methods and...

Homework Statement near the surface of the Earth there is an electric field of about 150 V/m which points downward. 2 identical balls with mass 0.540 kg are dropped from a height of 2.0 m, but one of the balls is positively charged with q1 = +650 uC and q2 = -650 uC. use conservation of...

This is not so much a homework problem as it is a question: How do I know whether an object has kinetic energy or potential energy? I know for potential energy you make a point that is PE(grav) = 0, and then if the object reaches a height you make the other PE = mgh. So in (KE_2 - KE_1)...

Please tell me how conservation of energy and mass apply in QM. I want to confirm something I read somewhere about QM not conserving energy.

Me and my roommate have being talking about the conservation of energy and the uncertainty principle and we are wondering if its possible to violate conservation of energy for brief periods of time or not. We have seen various interpretations of the energy-time uncertainty relations but cannot...

My question is "stupid"? I do have very specific questions and I accept your invitation to ask them... SpectraCat said: - "electrodynamics (i.e. Maxwell's equations) describes radiation from charged particles accelerating in a Coulomb field." So I was asking him which one of the...

i don´t quite understand: if you have a system made up of three pool balls. one of them is moving with a speed of 1 meters per second, the two other balls are standing still. if the moving ball hits the two other balls, in a way that the moving ball is standing still afterwards, then the two...

Hi Guys, I am doing an experiment to prove 1) Conservation of Energy 2) Inertia resist acceleration The experiment is simple, rolling objects down a ramp. So I timed the time taken for each object to reach the finishing line from rest. To prove conservation of energy, I increased the...

Homework Statement A 2.4kg block is dropped onto a spring from hieght of 5m. When the block is momentarily at rest, the spring is compressed 25cm. Find the speed of the block when the compression of the spring is 15cm. answer: 10m/s Homework Equations K=\frac{1}{2}mv^2 U_g=mgh...

Homework Statement Consider the system shown in the figure with m1 = 23.00 kg, m2 = 13.60 kg, R = 0.13 m, and the mass of the uniform pulley M = 5.00 kg. Object m2 is resting on the floor, and object m1 is 5.00 m above the floor when it is released from rest. The pulley axis is frictionless...

Homework Statement A projectile is launched with a speed of 40 m/s at an angle of 60 above the horizontal. Use conservation of energy to find the maximum height reached by the projectile during its flight. Homework Equations KEi + PEi = KEf + PEf (Initial kinetic energy + Initial potential...

i have to say physics kicks my butt. i never worked so hard in my life to earn a D in a class. now, i have to take the lab for that course and they are trying to kill us! the TA tore up my lab partners work because he didn't like the way she presented it in her lab book! ok, so that is what i am...

Homework Statement 1.)A particle is released from point A and moves in the potential U(x). Suppose the mechanical energy of the system is conserved. At which position(s) will the kinetic energy of the particle have its maximum value? 2.)A(n) 126 g ball is dropped from a height of 58.1 cm...

[b]1. Homework Statement [/b A 2.7 kg block is dropped from rest from a height of 4.5 m above the top of the spring. When the block is momentarily at rest, the spring is compressed by 25.0 cm. What is the speed of the block when the compression of the spring is 15.0 cm? Homework Equations...

Homework Statement A 10.0 kg mass slides from rest down a frictionless inclined plane from a height of 0.500 m. After traveling 5.0 m along the ramp, it moves along a horizontal surface (frictionless again) where it makes contact with a spring. The force constant of the spring is 100.0 N/m...

There is this cone that rolls uphill by itself, by shifting its centre of gravity. http://plus.maths.org/issue40/features/uphill/index-gifd.html" I wouldn't have looked up the mathematics of the issue if I hadn't seen it working with my own 2 eyes at a friend of mine's university physics...

Homework Statement Consider a head-on, elastic collision between massless photon (momentum Pnot and energy Enot) and a stationary free electron. Assuming that the photon bounces directly back with momentum p (in the direction of -Pnot) and energy E, use conservation of energy and momentum to...

1. In the system shown in the figure, the pulleys on the left and right are fixed, but the pulley in the center can move left or right. The two hanging masses are identical, and the pulleys and ropes are all massless. Find the upward acceleration of the mass on the left, in terms of g. 2. I have...

Learning the basics of quantum theory, one thing I can't quite grasp is how quanta, especially the e=hf equation, works within the law of the conservation of energy. I imagine the heat death of the universe for example, and taken to the extreme end all masses have been converted to energy...

This really isn't a homework problem with specific computations, rather it's a conceptual problem I'm struggling with; hence, the template doesn't really apply. (Please don't delete my thread!) In the derivation of the work-energy theorem W_C = \int_C \mathbf{F} \cdot d\mathbf{r} = T_2 - T_1...

I was watching this video, and it was saying that because the universe is expanding, the wavelengths of light waves were elongating, and therefore the energy of radiation throughout the universe is decreasing. They said that this defies the conservation of energy, but Einstein's general theory...

Something Vexing me about Magnetism and Conservation of Energy I have been thinking about an issue at work and it has been bugging me so I thought I would post something on here to see if anyone can explain where my thought process is going wrong. Say you have a super conducting magnet...

There is one thing i always wanted to ask. Since when HUP is so 'easily' allowed to explain the obvious non-conservation of energy? With what justification we say with such an ease that a particle can borrow(wtf does that mean?) energy ΔΕ but it must return it(what...??) in time Δτ? I really...

Homework Statement A ball is ikicked off a 100.0 m canyon at an angle of 30.0 degrees above the horizontal with a velocity of 24.0 m/s. What maximum height does it reach above the canyon floor? Homework Equations WNC = KE + PE The Attempt at a Solution WNC = 1/2mvf^2 - 1/2mvi^2 +...

Homework Statement A 2.00 kg block situated on a rough incline is connected to a spring of negligible mass having a spring constant of 100 N/m. The block is released from rest when the spring is unstretched, and the pulley is frictionless. The block moves 0.204 m down the incline before coming...

Take a capacitor arrangement...the capacitor having 2 plates which are square shaped. Assuming one of the plates as A and the other as B. If A has been given a static charge, it can be said that the all energy possessed by A can be computed when A is discharged...overall discharging will...

A uniform sphere is rolling without slipping on a horizontal surface at 2m/s. It then rolls without slipping up a hill to height h, where it briefly comnes to rest. Find the vertical height h. [The moment of inertia, I, of a sphere is 2/5 mR^2] where m is the mass and R is the radius of the...

I have come to this forum to see if someone can explain the following in non-mathematical terms. I board a steam train in Yorkshire and travel to London. I understand that energy is in the coal, which is burned and transforms some of the energy into heat which raises the steam which drives...

Homework Statement A small car is given an initial velocity of 4 m/s (prior to reaching the loop), what is the largest value that the radius of a loop the loop can have so that the car remains in contact with the track at all times? This one really has me stumped... please help

If a cart rolled down a ramp 5 meters high and flew off a a table at 3 meters high, what would its velocity be? please let me know where i go wrong, i was using the law of conservation of energy mgh1=mgh2+1/2mv2 mg(h1-h2)=1/2mv2 v=square root of 2g(h1-h2) where h1=5 and h2=3 i plugged in...

Homework Statement The water slide shown in the figure ends at a height of 1.50 m above the pool. If the person starts from rest at point A and lands in the water at point B, which has a horizontal distance L = 2.58 m from the base of the slide, what is the height h of the water slide? (Assume...

This is probably a product of how I was taught, but I am unsure of the status of conservation of energy in classical EM with point particles. Here is the background: When I was taught in undergrad, general arguments were used to show that there needs to be a back-reaction on a point particle...

In a pipe of varying diameter in which an ideal fluid is flowing, there's an increment in the kinetic energy of each particle as it reaches a region of lower cross section from a higher cross section in the pipe. Following the law of conservation of energy, there should be an energy transfer in...

1. Homework Statement Hi, I've been thinking about a formulation regarding "physical quantities" (that is, the quantities that specifically constitute the object of measurement for Physics), energy, and the conservation of energy. It would be very helpful for me that you could confirm me...

Homework Statement A bead slides without friction around a loop- the-loop. The bead is released from a height of 26.7 m from the bottom of the loop-the- loop which has a radius 9 m. The acceleration of gravity is 9.8 m/s2 . Diagram: http://img31.imageshack.us/img31/2377/19550530.png...

There is an interesting article here http://focus.aps.org/story/v18/st4 about a method for tunnelling light through usually opaque materials. Half way through they mention that one light ray becomes two: "When a light ray passing from glass into air strikes the interface at a...

Homework Statement A bullet of mass m = .010 kg and speed v passes completely through a pendulum bob of mass M = 1.2 kg. The bullet emerges with a speed of v/2. The pendulum bob is suspended by a rigid rod of length l = 0.50 m and negligible mass that can pivot about the center point...

Homework Statement A stone of mass m is at rest on a vertical spring which is compressed a distance x. Find its spring constant k. All variables are given in the problem. Homework Equations I solved this problem realizing that because the mass is at equilibrium, the sum of the...

Homework Statement A 0.200-m uniform bar has a mass of 0.790 kg and is released from rest in the vertical position, as the drawing indicates. The spring is initially unstrained and has a spring constant of k = 20.0 N/m. Find the tangential speed with which end A strikes the horizontal surface...

I have this situation here: I'm given the masses for the objects, as well as the radius and mass of the pulley. I have to use conservation of energy laws to find out how fast the mass on the right is going the instant it hits the ground. I can find out what the alpha of the pulley is...

SOLVED Homework Statement A 120g granite cube slides down a 40 degree frictionless ramp. At the bottom, just as it exits onto a horizontal table, it collides with a 225g steel cube at rest. How high above the table should the granite cube be released to give the steel cube a speed of...

Hi guys. I've decided to review my physics after a long time through Leonard Susskind's youtube lectures. I'm at lecture 2 and I'm already confused! in the 1st half hour, he gives a proof of the law of conservation of energy. In the course of this proof he uses the formula: F = -...

When you throw a ball in the ground you give it kinetic energy but because of the friction with the ground the ball come to rest. Where is the kinetic energy goes?! i know that the law of conservation of energy states that this conservation happened in closed-systems. but anyone has ideas...

Homework Statement A 1.9-kg block slides down a curved, frictionless ramp. The top of the ramp is 1.5m above the ground; the bottom of the ramp is 0.25m above the ground. The block leaves the ramp moving horizontally, and lands distance D away. A) What is distance D away? B) Suppose the...

Homework Statement A 0.030-kg bullet is fired vertically at 200 m/s into a 0.15-kg baseball that is initially at rest. How high does the combined bullet and baseball rise after the collision, assuming the bullet embeds itself in the ball? Homework Equations m1v1 + m2v2 = (m1 + m2) v'...

Quick question: I'm having trouble understanding a concept: say you've got a mass hanging from a peg by a string. Using conservation of energy, you can figure out what the minimum velocity is that the mass has to have initially so that it goes around the circle: at the top, mv^2/r = mg, so...

Homework Statement A spring has its right end fixed and is installed on a horizontal table so that the free end, in equilibrium, is at x = 3.00 m. A 1.65 kg block coming from the left slides along the table. When it passes the origin, it is moving at 5.58 m/s. It strikes the spring...