Conservation of energy Definition and 1000 Threads

Homework Statement The figure shows an 8.00 kg stone at rest on a spring. The spring is compressed by 10.0 cm by the stone. What is the spring constant? Homework Equations Elastic potential energy= \frac{k{x^{2}}}{2} Gravitational potential energy= mgh Spring force F= -kx The...

I've read that the Alcubierre Drive depends on the existence of negative mass, but I've seen that physicists say it could violate the conservation of energy. Their reasoning is that basically a negative mass and positive mass would interact in a perpetual motion sort of way that eternally...

I've often read posts where the conservation of energy is questioned regarding redshift due to expansion. The question arises because the energy level of photons is directly related to the light's frequency, and this alludes to photons "losing" energy as the frequency lowers. The reasoning I've...

Homework Statement A shot putter throws her shot. At the moment the 4.00 kg weight leaves her hand, it as a velocity of 14.0 m/s and is 2.00 m above the ground. The weight reaches a maximum height of 6.50 m above the ground before falling back down. What is the magnitude of the weighted...

Sorry if this is posted in the wrong place, I'm new to this forum. If an object in negatively charged and it is in oscillating motion is produces light waves which have energy. Does this mean that if I had a negatively charged pendulum in a vacuum (no friction/air resistance) it would...

Okay, so as I understand it, matter and energy can't be created nor destroyed, only converted from one form to another. So the question I have is, does that mean the total amount of energy in the universe is always the same? Presumably it is energy that is driving the accelerated expansion of...

Please look at pictures. There is something really weird going on. They say the bob has to make a vertical circle. Then, in the solutions, they say that, for that to happen, speed at top must be greater than zero. BUT, since the only force acting is mg, that means that mg=mv^2/r. <=>...

Homework Statement A long, uniform spiral spring of total mass m and spring constant k is suspended vertically from a fixed point. A much larger mass M is attached at the other end and allowed to oscillate vertically. As the mass M moves up and down, the spring contracts and stretches...

Homework Statement A bungee jumper of mass m drops off a bridge and falls vertically downwards. The bungee cord is elastic with natural length L and stiffness k. Deduce that at the lowest point of the fall, the cord is stretched by an amount: x=mg/k(1+√(1+(2kl/mg)) Homework Equations...

Does the conservation of energy law apply to: i) The initial impetus that drove the Big Bang; ii) The inflationary phase of the early universe; iii) The present expansion and acceleration of the universe? If not, under what conditions/hypotheses do cosmologists admit exceptions to...

Homework Statement A spring with a constant k=10[N/m] is attached with a long rope to a weight of 0.05 kg. they both lie horizontally on the table. the string is stretched 10 cm and released and the weight travels 40 cm on the table until it halts. what is the coefficient of friction...

Homework Statement This is elementary level stuff and I am pretty much past this, and yet I can't seem to find a suitable way of explaining this.I was thinking about Potential Energy of a particle of mass m falling freely under gravity(ignoring air resistance, again, beginner stuff :P) from...

Homework Statement A 16 kg block is initially at rest on a rough horizontal surface (uk= .2). The block has a small explosive charge inside it. The charge explodes, splinting the block into two fragments and adding 76.8 joules of kinetic energy. The other 10kg slides 1.47m along the rough...

Why is it that when you drop something on a spring, that item dropped on the spring does not bounce back up to where you dropped it from?

I wanted to just make sure I was doing this right. The problem: A marble of mass M and radius R rolls without slipping down a track from height h1. The marble then goes up a frictionless track to a height h2. Find h2. I figure this has to be in terms of other variables, here is my work...

1. Starting from rest, a 64kg person bungee jumps from a tethered balloon 65m high. The cord has unstretched length 25.8m. The cord is modeled as a spring that obeys hooke's law with spring constant 81N/m and the person's body is modeled as a particle. The balloon does not move. a) Express the...

Homework Statement A dog takes a running horizontal leap off a 10 m cliff and jumps with a speed of 3 m/s onto a ledge 4 m below the height of the cliff. With what speed does he land on the ledge?Homework Equations KEi + PEi = KEf + PEf 1/2mvi2 + mghi = 1/2mvf2 + mghfThe Attempt at a Solution...

I read this on a website called Physics for Idiots "If an electron gets near another electron it emits a virtual photon which is absorbed by the second electron and let's it know it need to move away." If a virtual photon is absorbed, doesn't than make it real, and so break conservation...

Homework Statement Hello, I'm having a problem with this. So we drop the weight on this spring, and the question is: how much does the spring compress? The mass is 5kg, the height 0,4m, and the spring elasticity factor k=1700N/m. Homework Equations The Attempt at a Solution I've...

Homework Statement I have a homework assignment that I am stuck on using the attached table. Problem 1: I have to find the velocity when given the mass and height. Problem 2: Then I have to find the height when given the velocity and mass. Homework Equations P.E. = m*g*h K.E. =...

The law of Conservation of Energy states that in a closed system (the entire universe or the Earth and Moon?) the total amount of energy is conserved through time. The gravitational interaction between the Moon and Earth creates tides. Humans can use these tides to create electrical energy...

Homework Statement You are just starting a new job as investigator for the car collision investigation. You assist your superior in order to determine, as accurately as possible, the circumstances surrounding collisions (initial velocity of the vehicles involved, direction vehicles were...

Hi, Could someone help me solve this question , my working has been attached & question, please point out errors. Help is greatly appreciated .

Ok, I'm driving myself mad, so if someone could settle this for me, that would be helpful. So, I'm imagining something like a hockey puck going across ice and coming to a stop. I'm trying to account for the initial energy, Ei, and the final energy, Ef. So this hockey puck starts with a velocity...

Homework Statement Lets say I have a spring with a stiffness of k = 250 N/m originally unstretched. I then gently place a 5 kg block on top of the spring. How much does the spring compress? Homework Equations W = mg F = -ks mgΔh = 0.5k(Δh)2 The Attempt at a Solution Using...

How is conservation of energy experimentally verified if some energy is dissipated, for example, as heat in air friction or friction with a road?

Homework Statement Homework Equations K = E + U E = 1/2mv^2 U = mgh The Attempt at a Solution So I think that for a, half the final velocity of m is equal to the initial velocity of 2m. So that's v = sqrt(2gr)/2? Momentum is not conserved because normal force and gravity are...

The mass is released at height h above the spring, how far will the spring move? Ei=mgh,Ef=kx2/2+mgx...why the second equation isn't Ef=kx2/2−mgx? Since it is below the "zero".

Homework Statement A particle P of mass m is attached to one end of a light string of natural length l whose other end is attached to a point A on a ceiling. When P hangs in equilibrium AP has length 5l/3. Show that if P is projected vertically downwards from A with speed √(3gl/2). P will...

Homework Statement Hi everyone, my teacher gave this problem as an extra credit for last exam, which I just did very bad. The figure is attached to the post. There are 2 objects, which have the same mass (m). 2 objects are connected to each other by a string length (L), which is massless. At...

" The potential energy U is equal to the work you must do against that force to move an object from the U=0 reference point to the position r. The force you must exert to move it must be equal but oppositely directed." The above definition is from hyperphysics. U = -GMm/R According to...

Homework Statement Homework Equations E = K + U K = 1/2mv^2 u = mgh The Attempt at a Solution Sorry if it's hard to read:

Homework Statement Particle goes to free fall from point ##A## to point ##B##. ##\upsilon_{A}=0##. How to define law of conservation of energy. Coordinate system is selected in such way that ##y## coordinate od point ##A## is zero. (See figure energy) Homework Equations For free fall...

Homework Statement A billiard ball moving at 2.58 m/s collides elastically with an identical ball initially at rest. After the collision the speed of one ball is 1.36 m/s. What is the speed of the other? Homework Equations K1+K2=K1'+K2' or P1+P2=P1'+P2' The Attempt at a Solution I get...

Homework Statement In deep space a 7.0 kg rubber ball moving along the x-axis with a speed of 20 m/s collides ELASTICALLY with another ball of mass = 25 kg. After the collision the 7.0kg rubber ball's velocity is directed in the positive y axis. Find the final speed of the 7 kg ball, as well...

Disclaimer: I am by no means an expert in the subject of physics. Apologies in advanced for improper term use or other mistakes. A documentary I was watching on Discovery channel explained that Jupiter's gravity acts on its moons to such a degree that it causes them to change shape, in the...

Homework Statement A 2 meter long pendulum passes its lowest point with a velocity of 4 m/s, then swings back up before temporarily coming to a stop. What angle does it then form with the vertical, if the air resistance is negligible? 2. The attempt at a solution I know that the...

Homework Statement Use the conservation of energy law to find the speed of the blocks and the angular speed of the pulley when the heavier block hits the ground. The system starts at rest. (going to include picture) http://i.imgur.com/CjB3gzK.jpg Homework Equations Moment of inertia for...

I would like to re-start the discussion regarding conservation of energy in the many worlds interpretation. Kith did not agree with my example, so hopefully it becomes clearer now where I see problems regarding the interpretation. Let's prepare a particle in a state like ##|\psi\rangle =...

Homework Statement A block of mass 5kg is released from rest and slides down a distance D down a smooth plane inclined at 30◦ to the horizontal. It then strikes a spring compressing it 10cm before it begins to move up the plane. If the spring constant is 980 N/m and g=9.8m/s², find D. Solve...

Homework Statement Using the Principle of Conservation of Energy, solve: A block of mass 5kg is released from rest and slides down a distance D down a smooth plane inclined at 30◦ to the horizontal. It then strikes a spring compressing it 10cm before it begins to move up the plane. If...

A 20 Kg. mass slides up on an infinitely long inclined plane (that forms an angle of 30º with the horizontal) with a velocity of 12 m/s. It's known that the mass returns to the starting point with a velocity of 6 m/s. Find,μ, the coefficient of friction between the plane and the body. This is...

Homework Statement A small circular object with mass m and radius r has a moment of inertia given by I = cmr^2. The object rolls without slipping along the track shown in the figure. The track ends with a ramp of height R = 2.5 m that launches the object vertically. The object starts from a...

Homework Statement Homework Equations Energy of a moving particle = γmc^2 Momentum of a moving particle = γmv The Attempt at a Solution I feel like there is something wrong here...I know I'm supposed to find the VERTICAL component of velocity, but can the total velocity...

Hi, GR permits wormholes hypothetically right? But surely they should violate conservation of energy because if one were to put one mouth in the ground an the other in the sky then you could enerate infinite energy by continually falling through them. Am I wrong? any help appreciated.

[b]1. A car of mass 800kg is at rest. The engine exerts a resultant force of 2000 N for a distance of 5m. a) What is then its kinetic energy? b) What is then its speed? [b]2. It is required that you must not use any SUVAT equations while solving this problem. Possible equations to use...

Homework Statement http://i.imgur.com/aeleeB9.png Above is a diagram of a simple two-block mechanical system. Block A is initially sliding with some initial velocity and Block B is initially at rest. Block A and block B collide, stick together, and begin moving with some final velocity...

Homework Statement In a physics lab experiment, a spring clamped to the table shoots a 22g ball horizontally. When the spring is compressed 22cm , the ball travels horizontally 5.2m and lands on the floor 1.4m below the point at which it left the spring. What is the spring constant...

Problem Statement: The system consists of a 20-lb disk A, 4lb slender rod BC, and a 1-lb smooth collar C. If the disk rolls without slipping, determine the velocity of the collar at the instant theta=30 degrees. The system is released from rest when theta= 45 degrees. Above I attached a photo...

Homework Statement An outfielder throws a baseball with an initial speed of 79.0 mi/h. Just before an infielder catches the ball at the same level, its speed is 65 ft/s. How much of the ball's mechanical energy is dissipated by air drag? (The weight of a baseball is 9 oz.) Homework Equations...