Conservation of energy Definition and 1000 Threads

Homework Statement A billiard ball moves at a speed of 4.00 m/s and collides ELASTICALLY with an identical stationary ball. As a result, the stationary ball flies away at a speed of 1.69 m/s. Determine a. the final speed and direction of the incoming ball after the collision b. the direction...

From what I can read on the web, it seems poeple don't agree wether or not dark energy violates conservation of energy. For some, as dark energy density is constant and the Universe expands, the total energy grows. For others, that growing energy is compensated by a growing negative...

Hi Everyone! I have done three years in my undergrad in physics/math and this summer I'm doing a research project in general relativity. I generally use a computer to do my GR computations, but there is a proof that I want to do by hand and I've been having some trouble. I want to show that...

Homework Statement I saw this problem from a few years ago here on Physics Forum (https://www.physicsforums.com/threads/work-energy-theorem-problem.823990/) and wanted some clarification. Here is the problem: A curved plate of mass M is placed on the horizontal, frictionless plane as shown...

Homework Statement Hey all, another problem. There is a 1 meter wooden panel that is on a frictionless surface. A puck is placed on one end of the panel and is pushed towards the other side. The mass of the panel is 10 times that of the puck. Also, there is a friction coefficient of uk=0.15...

Homework Statement Two blocks are connected with a massless, non-stretchable rope, and connected to a spring that is fixed to a wall. One of the blocks is hanging from the side of the table, while the other lies on the table. The mass of each block is m=1.0 kg, spring stiffness is k=50 N/m...

Homework Statement A fireman of mass m slides a distance d down a pole. He starts from rest. He moves as fast at the bottom as if he had stepped off a platform a distance h≤d above the ground and descended with negligible air resistance.What average friction force did the fireman exert on the...

I understand the 1st law of thermodynamics developed as a generalization based on experimental observations, in that an exception has yet to be found in thousands of situations, so it is considered to hold true in all possible situations. If that is how it developed, is there any other theory or...

For collisions between particles, Fdt goes to zero while Fdx does not F = mdv/dt mv + Fdt = mv if you have two particles colliding mva + mvb +Fdt = mva'+mvb' in the above case, Fdt goes away as there are equal and opposite forces between the two particles during the collision, linear momentum is...

A consequence of Heisenberg's Uncertainty principle is that particles energy level can fluctuate their amount of energy, e, for a short amount of time, t, as long as e x t < h/4pi (where he is = to Planck's constant). So does that not violate the law of conservation of energy?

Homework Statement Please see the attached photo. (down) Hminitial= 1.5R M = 2/3m Perfectly elastic collision What is the velocity of object m immidiatly after the collision? (by m,g,R) Homework Equations Conservation of energy Conservation of momentum The Attempt at a Solution I assumed...

Hello! I am having problems with this exercise if someone can please help me. Homework Statement In order to go all the way around a frictionless circular loop of R=2.5 m , how fast must a mass be moving as it exits at the bottom of the loop. 2. The attempt at a solution I am doing this...

Homework Statement What % of PEg must be converted in KE in order to double the speed of a pendulum? So I have spent a couple of days trying to figure out this problem (it's a lab), and I can't seem to figure it out. I have asked my physics teacher about it, and he said the answer to the...

Homework Statement If it can be assumed that the car has the same speed at points A and E, which of the following statements is true? a. The net work done in this system is 0 b. The net work done in this system is positive c. The net work done in this system is negative d. The net work done in...

Homework Statement A block of mass 10kg starts at the top of a frictionless track which forms a quarter circle with radius 10m. It is given an initial downward velocity of 10m/s. What is the velocity at the bottom of the track? Homework Equations KEtranslational, f+ KErotational...

Homework Statement a horizontal spring-mass is composed of a spring with constant 10.0 N/m and an 80.0 gram mass on the end of the spring. the surface supporting the mass is friction less. when the system is first observed, the spring is extended 1.30 cm and the velocity of the mass is 54.1...

Hello! I hope this is the proper forum for my question(s). English is not my native language, so I apologize in advance for language mistakes. In Feynman Lectures on Physics, there is a chapter about the conservation of energy. The first part, which deals with the definition of energy, I...

The second law of thermodynamics predicts the end of the life of the universe being one where thermal equilibrium exists throughout the universe (maximum entropy) - essentially all energy has been dissipated. My question is if according to the first law of thermodynamics which describes the...

Homework Statement Let two particles of equal mass m collide. Particle 1 has initial velocity v, directed to the right, and particle 2 is initially stationary. A: If the collision is elastic, what are the final velocities v_1 and v_2 of particles 1 and 2? B: Now assume that the mass of...

Since the universe is expanding, photons emitted by distant stars are red-shifted, having their wavelengths stretched out. But, since the energy of a photon is dependent on the inverse of its wavelength, doesn't that mean that the expansion of the universe is causing photons to lose energy? How...

Homework Statement Mechanical crane raises 225kg at a rate of 0.031m/s^2. from a rest to a speed of 0.5m/s over a distance of 4m. Frictional resistance is 112N. m1=225kg a1=0.031m/s^2 u1=0m/s v1=0.5m/s s=4m Fr=112N A. Work input from the motor B. Tension in the lifting cable C. Max power...

Homework Statement I am investigating a scenario where a pendulum with a bob attached is released from an angle and pushes a box to a certain distance. My goal is to find the coefficient of friction between the box and the surface it moved on. I have measurements for: - mass of the bob (125...

Homework Statement Playing in the street, a child accidentally tosses a ball (mass m) with a speed of v=23 m/s toward the front of a car (mass M) that is moving directly toward him with a speed of V=20 m/s . Treat this collision as a 1-dimensional elastic collision. After the collision, the...

Hi all, I have a little problem while reading Feynman lecture note volume 2, chapter 40, section 40-3. In that section Mr Feynman talked about Bernoulli equation and a example of a filled water container. In high school we learned that if we drill a hole near bottom of container, we can get...

Homework Statement Consider a massive pulley of mass m and radius r shown in the figure below, with two objects hanging off it having masses m and 2m, respectively. The pulley can be considered as a uniform disk, and the string is massless, does not stretch and does not slip. By considering...

1. Homework Statement A toy car coasts along he curved track shown above. The car has initial speed vA when it is at point A at the top of the track, and the car leaves the track at point B with speed vB at an angle ϴ above the horizontal. Assume that the energy losses due to friction is...

Hello, A dude I'm discussing momentum and kinetic energy with says this: "Place two masses in deep space, the only gravitational attraction is from each other. One of the masses is ten kilograms and the other is one kilogram. From Newton's Third Law we know that the mutual attraction is equal...

Homework Statement A 4.0 kg block starts at rest and slides a distance d down a frictionless 35.0 incline, where it runs into a spring. The block slides an additional 16.0 cm before it is brought to rest momentarily by compressing the spring, whose spring constant is 429...

Homework Statement Theres a pic. Homework Equations ##W_{friction}=W_{fr}=Δ(ME)## ##U_{spring}=U_s=\frac 1 2kx^2## The Attempt at a Solution I found (a) using ##W_{fr}=Δ(ME)## which ##v=7,4 \frac m s## For (b) I wrote;##\frac 1...

Special relativity states that according to an observer at rest, a measuring stick on a moving platform will appear shorter. Would this observer still see the measuring stick as comprising of the same amount of atoms as the observer who is at rest with respect to the measuring stick? If this is...

Homework Statement A super cue ball is made of the same material with the target ball (radius r) but slightly larger: rc = (3)^(1/3)*r The cue ball collides with the target ball on a frictionless table, as shown below, with initial speed of v0. The collision is not head-on, as shown below. a)...

Hello, This has been bugging me for some time now, so I would be interested to see what I have been missing so far. Imagine a single ray of light (made up of many photons) hitting a perfectly non-absorbing (for this wavelength of light) spherical dielectric object, which has finite mass. The...

Conservation of energy Is the law of conservation of energy absolute? If so, doesn't it follow that all the energy of the big bang came from somewhere? That the energy of our universe must predate the big bang? Isn't that circumstantial evidence of the validity of string theory which...

I'm having promblem with b. I checked the solution, but I did'nt understand the logic. Kf+Ugf+Usf = Ki+Ugi+Usi Usf= 0, Ki=0, Ugf= 0 I understand the logic's why they are equal to 0. I don't understand why final potential of spring (Usf) is equal to zero? ------------------ Now, I got...

Homework Statement 2. Homework Equations [/B] Inital energy=Final energy K.Ei+P.Ei=K.Ef+P.Ef The Attempt at a Solution

Homework Statement An object of mass m starts from rest and slides a distance d down a frictionless incline of angle (theata). While sliding, it contacts an unstressed spring of negligible mass as shown in the Figure below. The object slides an additional distance x as it is brought momentarily...

Homework Statement A ball is dropped vertically from a height H on to a plane surface and permitted to bounce repeatedly along a vertical line. After every bounce, its kinetic energy becomes a quarter of its kinetic energy before the bounce. The ball will come to rest after time? Homework...

Homework Statement A pumpkin was dropped from a balcony of a skyscraper. The pumpkin happened to land on a sidewalk force sensor and the below data was collected. The pumpkin weighs 2.7kg. a) From what height was the pumpkin dropped? b) From what floor of the skyscraper was the...

Homework Statement A 45 kg steel ball is projected vertically with an initial speed of 280 m s . While the ball is rising, 8.5E5 J of heat energy are produced due to air friction. What is the maximum height reached by the ball? Homework Equations Ek = 1/2mv^2 Ep = mgh The Attempt at...

Homework Statement A 10 kg initially at rest is pulled 13m across a floor by a 50N force. if friction does 380J of work over this distance, what is the block's final velocity? http://imgur.com/a/zM1MX Homework Equations W=Fd, Ek=1/2mv^2 The Attempt at a Solution Since the block was at...

Homework Statement A spherical satellite of radius r is moving with velocity v through a uniform tenuous atmosphere of density ρ. Find the retarding force on the satellite if each particle which strikes it (a) adheres to the surface and (b) bounces off it elastically. I know the answer should...

Homework Statement THIS PROBLEM CONSISTS OF NOTHING MORE THAN WHAT IS BEING STATED (NO VALUES, NO EQUATIONS, NOTHING) THIS IS A WORD PROBLEM WHERE NO CALCULATIONS ARE TO BE MADE: A mass hangs from a vertical spring and is initially at rest. A person then pulls down on the mass, stretching the...

Homework Statement A firework is shot from the ground at a speed of 50 m/s and an angle of 45 degrees. At its highest point it blows up into two pieces due to internal forces. One piece (.25 mass) falls straight down to the ground below the explosion, where does the second piece land? Homework...

Homework Statement So during collisions between 2 point masses, I know that momentum is always conserved, but energy may or may not be conserved. Now, in this case, where we have a block colliding with a pivoted rod, I know that angular momentum is always conserved, but neither energy or...

Homework Statement A 259 g textbook slides up a 22.1° incline that is 2.55 m long. Using conservation of energy and assuming the incline is frictionless, what minimum initial speed is needed to accomplish this? mass = 0.259 kg Θ = 22.1° length of incline = 2.55 m Homework Equations KE =...

Homework Statement Calculate the escape velocity on the surface of the neutron star in the previous problem (##m = \frac{2}{3} \cdot 2,1 \cdot M_{\odot}##; ##R = 15km##). Hint: Basic physics. Note, however, that the escape velocity is not going to be small when compared to the speed of light...

Homework Statement Ball mass = 0.0027 kg PE (0.5 meters) = 0.01323 J height of ball after three trials = 0.19 meters KE before bounce = 0.01323 J PE at new max height = 0.00503 Total energy = KE + PE Ke after bounce = ? Homework Equations mgh The Attempt at a Solution I did a lab where I...

Homework Statement Masses A and B, each having a mass of 32.2 slugs, are constrained to move in frictionless slots. They are connected by a rigid, massless rod of length L = 2 ft. Mass B is connected to two massless linear springs, each having a spring constant k = 60 lbF / ft. The springs are...

Homework Statement A very Slippery ice cube slides in a vertical plane around the inside of a smooth, 20 cm diameter horizontal pipe. The ice cube's speed at the bottom of the circle is 3.0 m/s Vi = 3.0 m/s Height at top= 2(.20) = .40 Vf = ? Homework Equations KE(initial) + PE(initial) =...

Why do conservative forces conserve mechanical energy while non conservative forces do not? According to me, What makes the conservative forces path independent is that for a particular case they always act in a fixed direction irrespective of the direction of motion of the object on which they...