Questions tagged [energy-conservation]

The law of conservation of energy, which states that the amount of energy in a system is constant. For questions about Earth's environment, see the climate-science tag instead.

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Shouldnt it be $\frac{mv^2}{2}$ through out the spring? Why do different $dm$ masses have different velocities?

I don't understand why you need integration in this question. Shouldn't it be $\frac{mv^2}{2}$ throughout the spring? Why do different $\mathrm{d}m$ masses have different velocities? A spring of ...
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Does it always take the same amount of energy to get from A to B?

Imagine you have a point A and a point B. Does it takes the same amount of joules to travel from A to B no matter how you do it (if in neutral conditions e.g. no wind)? For example, walking, riding a ...
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COM frame for photons

We know that there is no frame in which the energy of a photon is zero and hence it has zero momentum. But can we find a frame in which the energy of two head on photons is zero, or the center of mass ...
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Work and energy: law of conservation of energy? [duplicate]

According to the law of conservation of energy: Energy can neither be created nor be destroyed Then how did energy come into existence?
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Producing Pressurized Hydrogen Underwater Then Using it To Do Work

This is a bit of a weird one but I didn't know where else to ask this. I was recently talking to my brother and he told me about an idea he had talked with his boss about how to create compressed ...
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Conservation of energy in superconducting transitions with Meissner effect

In Type I superconductors the transition from normal to superconducting state occurs exactly at its transition temperature. Does this mean that we could theoretically use only a little bit of energy ...
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Can particles gain energy during inelastic collision?

We know that when two particles collides inelastically, the net energy equation is given by $$E_i=E_f+Q$$ where $E_i$ and $E_f$ are initial and final mechanical energies of the particles and $Q$ is ...
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Motion of a Particle in a Penning Trap, parameters and solutions

Ideal equations for motion of a charged particle in a Penning Trap are: $$ x(t) = \rho_{+}\cos(\omega_{+}t + \phi_{+}) + \rho_{-}\cos(\omega_{-}t + \phi_{-}) $$ $$ y(t) = (\frac{q}{\lvert q\rvert }) [...
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Understanding the big difference between input power and output power of system

Screw jack. ( Please see the above picture ) According to screw jack formula F=w×p/2πr ( without friction ) Here F= force , w= weight , p= pitch of the screw , r=length of the lever . Now i want to ...
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What is the reason for this apparent paradox caused by a massless spring with a locking mechanism?

Imagine that a ball of mass $m$ is launched at a block, which also has mass $m$. Attached to the block, facing the ball, is a massless spring with a massless board at the end. Alternatively, we can ...
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Energy budget in a buoyant flow

A cavity, subject to gravity, is filled with a fluid initially at uniform temperature. Initially all boundaries are adiabatic surfaces; at time $t=0$ two opposite boundaries (shown in red and blue) ...
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Variance between the energy required to lift/push a particular object to any height, and the potential energy of that object at that particular height

As shown in figure we have two objects , 1 and 2 . Each have a mass of 10 kg and height 1 meter. Suppose i lift object 1 to a height 1 meter. The energy required to lift object 1 is E= mgh ( m is mass,...
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Work-energy principle: What if there is no change in KE, but change in PE?

So I've been taught that the work-energy principle says that the total work done on an object is always equal to the change in kinetic energy of an object. Now let's say that I have a car moving up an ...
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Where does half of the work done in charging a capacitor is dissipated? [duplicate]

The energy stored in a charged capacitor of capacitance $C$ with $V$ voltage across it is: $$U= \frac 12 CV^2$$ Whereas the work done in charging the capacitor is: $$W= CV^2$$ This means that $(1/2)CV^...
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Conservation of energy in explosion

Suppose a shell rested on a smooth surface fires a bullet horizontally ,generating some energy of explosion say E. I know that initially system(shell+bullet) has no energy. When the internal forces do ...
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Why is the loss of energy maxed in perfectly inelastic collision?

I was doing a physics problem, and it had asked me to find the maximum $K_e$ loss, but I don’t understand why the loss is maxed when the objects stick together (the collision is inelastic).
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Finding the angle of inclination given the work done by friction [closed]

My question pertains to part (ii) of the following question: In part i, I found that the speed at point B is $ 7 m/s$. Now, in part ii, there are two ways to approach the question. The first uses the ...
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Energy conservation in projection of a charge [closed]

The question reads, "A positive point charge of mass m is projected with a velocity inside the tunnel as shown. The tunnel has been made inside a uniformly charged non conducting sphere. Find the ...
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4answers
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Perpetual motion: Conditions for rolling a wheel sliding on a bar [closed]

This is a basic question about energy conservation and classical mechanics: Question: Under what situations can this motion be perpetual? Without gravity and without frictions. Without gravity and ...
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Water flow from overhead tank

When water is flowing from an over head water tank as shown in the associated picture, Would water lose all it's kinetic energy due to friction in pipe and thus stop flowing ,if the pipe is ...
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Energy stored in the curvature of spacetime?

Lets assume there are particles with mass. If the mass is big enough, they will accelerate toward the center of mass. Thus the particles gain kinetic energy and hence the total mass gets bigger. Since ...
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To find the angle of slipping of a falling coin

In an attempt to predict the outcome of a toss, I dropped a coin with its edge just touching another sharp edge as shown in figure. (The edge is flat and sharp with very less friction as in case of a ...
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1answer
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What preconditions should be satisfied to make energy conservation law possible?

Let us consider a system whose evolution is given by dependency of $N$-dimensional real-values vector on time: $\vec r = \vec r (t)$ (or in terms of components $x_i = x_i (t)$). Let us also assume ...
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Does momentum change when Kinetic energy changes?

$K.E=\frac{1}{2}mv^2$ , $P=mv$ thus there is a relation between them. I really can't understand why there is no decrease in momentum when kinetic energy is decreased in an inelastic collision. I am ...
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Can why gyroscopes don't fall be explained by conservation of energy?

you know how when you spin a gyroscope it supernaturally stays up even if you bend it over and its parallel to the ground? Well that was unbelievable so I did some math to see why this works. I tried ...
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What form of energy was the energy of the universe before the Big Bang? [duplicate]

It is said that all the energy of the current universe originated from the Big Bang. The first law of thermodynamics states that energy can neither be created nor destroyed simply converted from one ...
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Does work between 2 bodies depend on their relative speed?

Imagine a car standing on the road. Now the car starts to accelerate. On the first part, the car accelerates from 0 m/s to 10 m/s. Some of the fuel was used during this first part. let's call that ...
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Sum of the four-momentums of the system: sum of norms or norm of the sum?

The observer is at rest at point O. At once, he shots two bullets with equal masses $m$ in the opposite directions. Their velocities are equal by modulo $v=v_1=-v_2$. Now, he wants to calculate the ...
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What happens to the rotational kinetic energy? [duplicate]

There is a classic example that a spinning skater pulls his arms back. The angular momentum is conserved, the moment of inertia decreases. And therefore, it's angular velocity increases, so the ...
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Is total Universe “total” Energy relative?

I have read a lot about (what is the total energy of universe? And Is it zero?) here, such as, Is the total energy of the universe zero? and other sources. I thought decades about a question, not ...
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Why does the Schrodinger equation depend on conservation of energy if conservation of energy is violated

The Schrodinger equation: -((h^2)/8 pi m)(d^(2)psi(x)/dx^2)+v(x)psi(x)=E psi(x) is just another way of writing : kinetic energy + potential energy = total energy right? (for those of who can't see ...
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Earth rotation: What provides the energy? [duplicate]

We all know the earth is rotating around its own axis. From a physics energy point of view, some thing has to provide energy for the rotation. What provides the energy to rotate?
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Bungee jumper and conservation of energy

A bungee jumper of mass $75 kg$ is standing on a platform $53 m$ above a river. The length of the upstretched bungee cord is 11m. The spring constant is $65.6 N/m$. Calculate the jumper's speed at $19 ...
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Energy and momentum conservation laws in special relativity

In special relativity the energy of a material point is defined $$E= \frac{m_0}{\sqrt{1-v^2/c^2}}c^2,$$ and the momentum is defined by $$\mathbb{p}= \frac{m_0}{\sqrt{1-v^2/c^2}}\mathbb{v},$$ where $\...
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Threshold energy in relativistic collision: Frame choice matters for finding initial speed of proton? Conservation of energy alone doesn't work?

The situation is a proton colliding with a stationary proton with enough energy to create a pion. I know the typical way to do these problems is to use the center of mass frame, but I wanted to try it ...
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1answer
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Change in direction imply angular acceleration

Does direction change imply angular acceleration. When a non-point mass object changes direction (like a block sliding down a hill of changing slope), why do we not account for rotational $K.E$ when ...
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1answer
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Vertical circular motion inside a tube and with a light rod [closed]

I have a doubt that when the initial velocity given to a mass connected to a light rod fixed at one point, is $\sqrt{4gr}$ (given at the lowest point) then does it complete a circle or just reach ...
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Does a contracted spring become warm?

As far as I remember, if we stretch a solid iron bar mechanically, some portion of the work done by, say, the hydraulic pistons, makes the bar's temperature increase before it pulls apart. I want to ...
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Law of Conservation of Energy on chain falling from table

As shown in the figure, a uniform chain of length 𝑳 is placed on a smooth horizontal table, and 𝑳/4 of it is hanging down on the edge of the table. After letting go, the chain starts to slide down ...
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How deep does the pool at the end of a waterslide need to be?

I am looking at a problem where a woman has travelled down a simple waterslide and into a pool, then hurt her knee by striking the floor of the pool. I need to figure out how deep the pool needed to ...
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Does an AC circuit transmitting 20hz and 2khz audio frequency carry twice as much energy as a 40hz and 4khz frequency?

If a guitar pickup uses electromagnetic induction to induce AC current into a wire, does the low fundamental frequencies in that current carry more energy than the higher frequencies? This is not a ...
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Why Lenz's law works?

When we move a magnet towards a coil, current is induced in it. Magnetic field too develops around it. Since there is interaction of both magnetic fields(that of magnet and coil), there is magnetic ...
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1answer
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Does an electric field induced by a time varying magnetic field has an energy associated with it?

Consider a time varying magnetic field. This induces an electric field upto infinity as per Faraday law and other related laws. Is energy stored in this induced electric field? If so, what kind of ...
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Does conservation of energy hold in quantum mechanics? [duplicate]

Say we have a particle in an infinite deep well that is $V(x)=\left\{\begin{array}{ll}0 & 0 \leq x \leq L \\ \infty & \text { elsewhere }\end{array}\right.$. The energies corresponding to ...
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Can rolling without slipping occur without friction?

If a body is rolling without slipping is it necessary that there is friction acting on it ? I encountered a question in which there is a spherical body and a force is being applied on its top point ......
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Atom kinetic energy transfer

So according to physics laws, energy can't be created or destroyed but transformed from one form to another. But what happens when an atom flows with certain velocity and is stopped by other atom's ...
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Energy Conservation: How is Heat generated in a loop with Time Varying Magnetic Field through it?

Consider a circular loop kept in a time-changing magnetic field. We know, via Faraday Law, that EMF is induced across the loop and hence a current appears in the loop. Let there be some Resistance ...
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Standing wave and energy conservation

Consider a one-dimensional standing wave formed on the interval $0 \leq x \leq L$. Let's say that this is an ideal model motivated by a string as a medium with both ends closed. Assume that there is ...
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1answer
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Where is mass defect in nuclear fusion? [duplicate]

The hydrogen is one proton and the helium is two protons and two neutrons. Neutron is a little heavier than the proton. But there is something strange. Where is the mass defection? As a result, the ...
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2answers
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Where the energy stored in magnetic field goes?

When we bring a magnet towards a coil, current is induced. As magnetic field is generated around coil and there is interraction of magnetic field lines with external field, energy is stored in field.(...

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