In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.
Homework Statement
We have a system with N particles with masses m1, m2, ... mN and electrical charges q1, q2, .. qN that interact electrostatically. We assume these interactions are instantaneous. Construct the formula for the total energy and show that this is conserved.
The Attempt at a...
How to determine the total energy of matter in the universe
Hi all,
while looking at a table of order of magnitudes of energies in nature, I just realize that I really don't know how to determine the total energy contained in the universe (near 10 to the 69).
Can someone get this number...
Hi,
a question at work popped up and it's been too long since I went to school :p
The total energy [Wh] required to heat the system to temperature T is given by f(T)=1.28T. The effect [W] applied to the system is given by g(T)=378-3.16T. How long does it take to heat the material to say 80...
Homework Statement
A rollercoaster cart
mass = 55kg
velocity = 5m/s
height = 5m
what is the total energy that the cart has at this position?
Homework Equations
would s=d/t be relevant?
The Attempt at a Solution
already calculated
gravitational potential energy: GPE = m*g*h =...
Homework Statement
Calculate the total energy of a 2kg mass that is undergoing simple harmonic motion with an amplitude of 1cm and and frequency of 16Hz.
Homework Equations
ma = -w^2x
The Attempt at a Solution
The first thing I thought was using the general solution of x(t) = A...
Homework Statement
I am trying to derive the total energy for an n-dimensional linear (Hookeian) spring-mass damper system and show that the total energy is either decreasing or constant.
Homework Equations
1D spring-mass damper equation
n-D spring-mass damper equation
The Attempt at...
Homework Statement
Derive an expression for the total energy required to asemble a sphere of charge corresponding to a nucleus of atomic number Z and radius R. Assume the nucleus is a sphere of uniform volume charge density \rho
Homework Equations
\rho = mass / volume = 3Am / 4*pi*R3...
2 electrons in box, "hard" walls, total energy E.
Say we place 2 electrons inside an empty 1m cubed box with very "hard" walls, the electrons can penetrate only a very small distance into the walls of the box. Let us say that any photons produced by the scattering of the two electrons stay in...
What is the total energy of the universe?
I would like a gross energy, not a net energy, as I saw somewhere that the net energy of the universe is zero.
Is there a direct relation between the relativistic mass (total energy) and rest mass?
In other words, can we say a proton has higher rest mass than an electron because a proton-antiproton annihilation would produce that much more energy than electron-positron one? And the ratio of energy...
During the (recently departed) matter-dominated era, the total mass of the Universe, including dark matter, is believed to have been fairly constant at around 1055 kg. This was the case in a time period from at least the CMB last scattering surface to nearly the present. Mass content is...
Homework Statement
Hi
I am new to this forum and offering quantum physics at A level. Can anybody help with the following problem:
The rest energy of an electron is 0.511MeV. A positron created in a cloud chamber has 0.158MeV of kinetic energy. It collides with an electron at rest...
A mass of 0.5 kg is attached to the end of a massless spring of spring constant 0.40 N/m. It is released from rest from an extended position. After 0.7 s, the speed of the mass is measured to be 1.75 m/s. What is the amplitude of oscillation? What is the total energy (relative to the mass at...
Homework Statement
A loaded ore car has a mass of 970 kg and rolls on rails with negligible friction. It starts from rest and is pulled up a mine shaft by a cable connected to a winch. The shaft is inclined at 30.0° above the horizontal. The car accelerates uniformly to a speed of 2.20 m/s in...
Homework Statement
The element N has 7 electrons and 7 protons in the atom. An ion of N has all the electrons removed except 1, so it resembles a hydrogen atom with a nuclear charge of +7 e.
E1(Hydrogen)= -13.6eV, r1(Hydrogen)= 5.29x10^-11m.
k = 8.99x10^9 e = 1.6x10^-19
What is...
Why is the total energy of an elliptical orbit given by:
E_{tot}=\frac{-GMm}{2a}
Where a=semi major axis.
I agree for a circular orbit I can do the following:
F_c=F_g
ma_c=\frac{GMm}{r^2}
\frac{v^2}{r}=\frac{GM}{r^2}
v^2=\frac{GM}{r}
Since the total energy also equal to the kinetic plus...
Homework Statement
The power supplied by a certain battery is a constant 6 W over the first 5 min, zero for the following 2 min, a value increases linearly from zero to 10 W during the next 10 min, and a power that decreases linearly from 10 W to zero in the following 7 min. (a) What is the...
I'll ask this in the form of an example. A bus is traveling at some speed and there is no wind. The bus experiences a drag force related to the pressure differential at the front and rear of the bus. Most of the divergence in pressure from ambient occurs behind the bus, where the air is...
Homework Statement
Suppose I have a spherically symmetric static star. What is the total energy of (baryonic) matter inside the star?
Homework Equations
The metric is (parametrizing as in Weinberg):
ds^2=-B(r)dt^2+A(r)dr^2+r^2d\Omega^2
I assume the energy-momentum tensor of a...
The total energy of a pendulum is calculated either by it's maximum height (Gravitational Potential), or by the lowest point with maximum velocity (Kinetic Energy).
For the significant formulas of a pendulum see http://en.wikipedia.org/wiki/Pendulum_(mathematics)" wiki page
If you use the...
Alright, the problem is fairly simple actually; however, I've seen a few methods to solve this that have kind of confused me.
The questions is:
Consider a frictionless roller coaster with a mass of 12,000kg. If the coaster starts at rest at point A, which is 95m above the ground...
According to my physics textbook, the equation E^2=\left(mc^2\right)^2+\left(pc\right)^2 suggests that a particle may have energy and momentum even when it has no rest mass, and that the total energy then is E=pc. This strikes me as odd, since the relativistic momentum of a particle is given by...
Homework Statement
(a) A light particle of mass m orbits in a circular orbit around a massive attractive centre with a potential that is given by
V(r) = Cr^2
(b) Using the equations for circular motion show that the total energy of such a particle must be given by
E = 2Cr^2
Use...
Homework Statement
A charged particle is observed to have a total energy of 0.642 MeV when it is moving at 0.700c. If this particle enters a linear accelerator and its speed is increased to 0.980c, what is the new value of the particle's total energy?
Homework Equations
Rest mass...
Homework Statement
Alright so, there are two different parts that I am having trouble with for this question.
The first problem I need to calculate the total energy of a group of 12 electrons that each individually have a potential of 3 V. This is all that is given for the first part...
Homework Statement
An electron has a total energy equal to five times its rest energy(0.511MeV).
--What is its momentum (in MeV/c)?
Homework Equations
E(total) = [mass(electron)*c^2]/[sq. root of (1- velocity^2/c^2)]
----I converted 2.555MeV (total energy) to 4.088e-13 J and...
Homework Statement
it is a multi part problem i found most just need help on last two but gave answers to the ones i found because they are needed to determin the answer.
What is the translational kinetic energy of the real system, at the instant shown in the right diagram?
Ktrans =...
Hello,
I have measurements of the sound intensity produced by a sound source for a given frequency (*). These measurements were taken on on a grid on an imaginary sphere around the source. From these measurements it is clear that the sound intensity is not equal in all directions.
The...
Homework Statement
Explain why it is possible for potential energy and total energy to be either positive or negative, but kinetic energy is always positive
Homework Equations
The Attempt at a Solution
I'm thinking that Potential Energy and Total Energy can be opposite and take...
Homework Statement
A flash attatchment for a professional camera stores energy in a capactior. When a picture is taken, all of the charge is converted to energy, and the capacitor is fully discharged.
A.Assume the battery charging the capacitor is a 300V battery. When the light flashes, it...
Excuse this beginners question, but someone asked me if the Universe can appear out of nothing. I answered yes, because all the energy in the Universe cancels out to make nothing. So, conversely, out of nothing can come equal positive and negative energy. He seemed half convinced.
Am I correct...
Homework Statement
A solid sphere has a mass of 1.0 kg. It is rolling at a translational speed of 10 m/s. What is the total energy of the rolling sphere?
I think I got the problem but I'm not sure I went about it the right way.
Homework Equations
I = (2/5)mr^2
KE_rot = (1/2)Iw^2
KE =...
Hello!
I've just finished a discussion with my peers and lecturer on some of the postulates of QM,
My lecturer said that "the total energy of any quantum mechanical system is always given by the Hamiltonian, which may be obtained by appropraite application of the classical Hamiltonian"...
Hi all,
I have to compute the entropy, temperature and show that the total energy can be written as
E(T,N) = 3/2*N*hbar*omega*coth(hbar*omega/(2*kT))
I have found that the temperature can be written as
1/T = k/(hbar*omega)*ln([E/N*hbar*omega+3/2]/[E/N*hbar*omega-3/2])
by...
I have a question on the Hamiltonian from a classical viewpoint.
I understand that the Hamiltonian, H, is conserved if it has no explicit time dependence, in other words:
\frac{\partial H}{\partial t} = 0
What I am not clear on is how one can determine whether a given Hamiltonian...
Homework Statement
for this problem i found all of the separate capacitence for each capacitor, each potential difference, and each charge on each capacitor but I am not sure how to get the total energy stored for the whole system. does anybody know the correct equation
Homework Equations...
Many texts and research papers seem to argue the case for the total energy of the universe being zero or constant. Indeed the Friedmann equation is often derived in books using KE+PE=constant, where the constant is zero for a flat universe. The sign of the constant also determines whether the...
Fermi energy:
E_f =\frac{\hbar^2 \pi^2}{2m L^2} n_f^2
The number of states with energy less than E_f is equal to the number of states that lie within a sphere of radius |\vec{n}_f| in the region of n-space where nx, ny, nz are positive. In the ground state this number equals the number of...
Hello everyone, I hope someone can help me with this simple harmonic motion question
I've been trying it for about an hour now and I think i may have found the problem but I want to run it by someone else :)
I'm taking this Phsyics 12U course (Uni prep for Ontario, Canada) through correspondence...
I am looking for an expression for the total energy of a particle of rest mass m_0 that includes kinetic and gravitational potential, if there is such a thing. If I take the product of the time-components of the four-velocity and four-momentum vectors, I get
m_0 c^2 \gamma^2
where...
Thermodynamics asserts that energy can neither be created nor destroyed and thus the total energy of the universe is always constant. Thus the accelerating expansion of the universe indicates that some form of energy is being converted into another form at increasing rate? Can this be explained...
Homework Statement
A gardener exerts a force of 1.5 x 10^2 N (22 degress below the horizontal) in pushing a large 18 kg box of flower seeds a distance of 1.6 m. The coefficient of kinetic friction between the box and the floor is 0.55.
use the law of conservation of energy to determine the...
I was presented with a very simple physics problem today which unfortunately stumped me for some reason:
you have two spaceships: a cruiser weighing a ton, and a battleship weighing 100 tons. Now let's say the cruiser is moving towards the battleship at constant speed. From battleships point...
How can I measure the total energy loss of a Newton's cradle until it comes to rest. The only variables I am given are the horiztonal displacements for each swing (how far the ball travels out after it rebounds off the other balls) and the angle. I have no idea where to start, I was told I...
1. Homework Statement
Plot total energy vs. time graph using MATLAB (damped system)
wn(the undamped natural frequency) = 2 rad/s
damping ratio, z = 0.01
mass = 10kg
initial displacement = 0.1
initial velocity = 0
2. Homework Equations
KE = (1/2)mv^2
PE = mgh
3. The Attempt...
Hi all. I've this problem and I'm stuck on the part where I have to find the total energy.
Homework Statement
A 507 g mass oscillates with an amplitude of 10 cm on a spring whose spring constant is 20 N/m. At t =0s the mass is 5.0 cm to the right of the equilibrium position and moving to the...
1. The length of a simple pendulum is 0.760 m, the pendulum bob has a mass of 365 grams, and it is released at an angle of 12-degree to the verticle. (a) With what frequency does it vibrate? Assume SHM. b) What is the pendulum bob's speed when it passes through the lowest point of the swing? c)...
Homework Statement
An object of mass 2.00 kg is held at a position A, a vertical height of 20.0 m above the ground. Point B is 8.00 m directly below A. Neglect air resistance and use g=10.0 m/s(squared)
What is the ratio of the total energy of the object at position A to position B?
Homework...