# 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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### Rolling on a track in vertical plane

A sphere of mass m and radius r is released from rest at point A on a track in vertical plane. The track is rough enough to support rolling between A and B and from B onwards it is smooth. My ...
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### Potential Energy in conservation of energy [closed]

In energy conservation theorem, everywhere $PE=mgh$ is used. What I found is that change in PE= mgh. According to me, while calculating total energy, instead of change in PE, total PE should be used ...
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### Question about Helmholtz's paper “ON THE CONSERVATION OF FORCE”

Below follows the exact extract from Helmholtz's paper "On the conservation of force". Let us now imagine, instead of the system $A$, a single material point $a$, it follows from what has been just ...
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### Confusion regarding the conservation of mechanical energy

If it's always the case that---when all forces are derivable from a potential energy---$$\Delta T = W = -\Delta V$$ so that $$\Delta \left(T + V\right) = 0,$$ why is energy not conserved when $V$ is ...
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### Is energy conserved in a Van der Pol oscillator?

The Van der Pol Oscillator is governed by a 2nd order ODE with nonlinear damping. The 'position' of the oscillator is the solution to $$x''(t) = \mu (1 - x^2(t)) x'(t) - x(t)$$ Here $\mu$ controls ...
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### Is this statement true for all conservative forces or just attractive conservative forces?

'Change in potential energy is always equal to the negative of the work done by a conservative force.'
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### How to calculate velocity of an object at the bottom of a circular hill if there is an energy loss due to friction?

Object slides down a circular hill and loses some of its initial mechanical energy due to friction. As an object slides down, friction increases and force in direction of motion decreases until the ...
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### Mechanics Question - Bullet fired into Block

I am studying for the GRE and came across this question (Question 93 from Sample Exam 2 in Kahn and Anderson's Conquering the GRE): A bullet of mass 5 g is fired at a block of wood of mass 1 kg, ...
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### How is energy conserved in this case?

Consider a permanent magnet introducing a magnetic field at some fixed angle to a loop of wire on a spindle. If a fixed current is allowed to run through the wire, the lorentz force introduces a net ...
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### How does $dS \ge 0$ imply a system cannot receive more energy than work supplied?

I am reading a book that asserts the following: The second law arises from an equation of the form $$dS = \mu\,dE + \mu\,dW \tag{1}$$ where $dS$ is the change in entropy, $dE$ the change ...
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### Energy in inertial frame of reference

If a body A is moving with a constant velocity v and an observer on that body A observes another body B to be at rest then the kinetic energy of B is zero. So is energy dependent on the frame of ...
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### How does flow work arises in enegy balance using Reynolds Transport theorem?

I will use the below mentioned form of Reynolds Transport theorem(usually derived in Fluid Mechanics context) to give a relation between a Control mass system(no mass in or out) and Control Volume(...
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### What happens to the energy of an absorbed photon?

Photons are electromagnetic wave fields that travel at the speed of light. When they are absorbed by an object, their momentum and energy is transferred to the absorbing object. What is that ...