Potential energy Definition and 1000 Threads

Hello! The (potential) energy of an electron in a solid structure is always negative; also the E_c and E_v levels (conduction band and valence band limits) are negative, in the band diagram of a pn junction. When the junction is built and thermal equilibrium is reached, the depletion region...

Homework Statement Homework Equations The Attempt at a Solution Kinetic Energy + Potential energy=0 1/2mv^2 = mgcos(20) 100v^2 = 1.96cos(20) v^2 = .0184 v = .136 m/s No idea if this is correct or if I should proceed with energy considerations. Please advise.

Homework Statement A child starts from rest and slides on a sled first slope down over a distance of 25 m . Then, the child slides further over a horizontal plane. The angle of inclination is 35 ° and the kinetic coefficient of friction between the sled and the snow is 0.100. The mass of the...

I have read posts about this but still don't have a good handle on it. I am confused about something that I know is simple. If a mass is attached to a spring, the spring will stretch according to Hooke,s law, correct? So won't the weight, (mg) balance out the spring force of -kx? So in other...

While studying energy conservation on Morin I found this explanation about the work-energy theorem for a system. Using Koenig theorem $$\Delta K_\textrm{system}=\Delta K +\Delta K_\textrm{internal}$$ so we have I've got two main question on that: Why are only external forces considered for...

For a conservative force \vec{F}=-\vec{\nabla} U \implies dW=-\vec{\nabla}U \cdot d\vec{s} Where d\vec{s} is the infinitesimal vector displacement. Does the following hold? -\frac{\partial U}{\partial \vec{s}}=-\vec{\nabla} U \cdot d\vec{s}=d W, i.e. the infinitesimal work is minus the...

1- Potential energy stored in a dipole placed in an electric field E is maximum when a- E is perpendicular to the dipole moment b- E is parallel to the dipole moment c- E is anti-parallel to the dipole moment

Homework Statement Homework Equations Find Time Period. Find the error in my solution. The Attempt at a Solution Where i am wrong ?

I do not understand the reason why a conservative force always "tries" to reduce the potential energy of a system at its minimum (forgive me if I said it in a wrong way). The explanation I gave me is: since for a conservative force, from the definition of potential energy, W=-\Delta U that...

Homework Statement A 400-N child is in a swing that is attached to a pair of ropes 2.00 m long. Find the gravitational potential energy of the child-Earth system relative to the child’s lowest position when (b) the ropes make a 30.0° angle with the vertical Homework Equations Ug=mgy The...

Could anyone help me with this sum - To generate electricity, 180000 kg water is dropped from a height of 50 m (let g = 10 m/s^2). If half the gravitational potential energy is converted to electric energy, how many 100 W bulbs can be lit ? Formula - Ep = mgh I calculated the potential energy...

Homework Statement An object with charge +2.0×10−5 C is moved from position C to position D in the figure (Figure 1) . q1 = q3 = +10.0×10−5 C and q2 = −20.0×10−5 C. All four charged objects are the system. Here's a picture to the problem Homework Equations $$ F = \frac {kq_1 q_2}{r^2} $$ $$...

Homework Statement A 975 g block is released from rest at height h0 above a vertical spring with spring constant k = 410 N/m and negligible mass. The block sticks to the spring and momentarily stops after compressing the spring 24.2 cm. How much work is done (a) by the block on the spring and...

Just signed up, hi everyone! 1. Homework Statement A man weighs 150 lb, and attaches a bungee cord having a stiffness of k = 500 lb/ft, to his feet. If he jumps from rest off the side of a bridge, determine the required unstretched length of the cord so that he can just touch the surface of...

1. Homework Statement For part (iii) , I used the principle of conservation of energy, K.E of the 2 kg particle after collision + E.P.E = K.E of the 2 kg particle at the furthest distance away from A + E.PE, But the solution for this question did not include the E.P.E of the string...

Homework Statement A proton is in a place where the electric potential is V, and as a result it has a potential energy E. If you replace the proton with an alpha particle (twice the charge of the proton and four times the mass) in the same place, it will experience an electric potential...

Homework Statement Two neutron stars are separated by a distance of 4.80 E 10 m. They each have a mass of 3.60 E 30 kg and a radius of 1.30 E 5 m. If they are initially at rest... How fast is each star moving when their separation has decreased to half its initial value? How fast is each star...

This pertains to a homework question but I get the concept of PE or U = -GmM/a for an elliptical orbit. I also understand the derivation of the total energy of an object in an elliptical orbit as E = -GmM/2a. However, I have a homework question that asks for the ratio of an object's kinetic...

When a particle (or any objects) accelerates when acted upon by fundamental forces, what is happening to the amount of energy in that particle? A large example would be an asteroid in space caught by Earth's gravity and accelerates toward Earth as a result. The fundamental forces here can be...

Homework Statement Homework Equations ΔU = Uf - Ui The Attempt at a Solution Would I have to make the left side of the equation equal to m*a*x? Is the x on the left side equal to -100 m?

Homework Statement The potential energy function for a system of particles is given by U(x) = −4x^3 + 3x^2 + 8x, where x is the position of one particle in the system. (a) Determine the force Fx on the particle as a function of x. Homework Equations du/dx[U(x)] = Fx The Attempt at a Solution...

given a force F = f(x) i^ + g(y) j^ + h(z) k^ (x,y,z,are coordinates of body) how can i prove or disprove that the force is conservative ?

I have 3 questions regarding the topic: 1-Why is that we are allowed to add or subtract a constant to a potential energy function V(x) to set it to zero where it is constant? 2-What does adding/subtracting a constant physically correspond to if anything at all? 3- Do we do it simply for...

Homework Statement In the figure below, a right triangle, determine the magnitudes of the a. Net e-field at p (assume a proton is placed at p) b. Net electrostatic force at P c. Net electrostatic potential at P let q = 1.70 x 10^-8, R = 78cm and P is halfway between Q1 and Q3 Red dot is P A^2...

In Griffith's "Introduction to Quantum Mechanics, second edition" he states: For the delta-function potential, when considering the scattered states (with E > 0), we have the general solutions for the time-independent Schrodinger equation: $$\psi(x) = Ae^{ikx} + Be^{-ikx}~~~~\text{for }x<0$$ and...

There's this problem that was given in my physics class.. "Three identical, negatively charged particles are situated at rest in a straight line, as shown below. All three are released simultaneously, and are free to move. Find the maximum velocities attained by particles A, B, and C. They have...

I am confused about the signs in calculating the potential energy change from the electrostatic force. Suppose there was a point charge +q1 and I moved a second point charge +q2 from a distance of b from q1 to a distance of c from q1. c is smaller than b. So the potential energy change is - ∫...

Homework Statement Potential energy in a molecule[/B] (b) The figure below shows all of the quantized energies (bound states) for one of these molecules. The energy for each state is given on the graph, in electron-volts (1 eV = 1.6 ✕ 10-19 J). What is the minimum amount of energy required to...

Since capacitors can store electrical energy in the form of a electrostatic field between its plates, one can derive that potential energy by looking at the work it takes to "push" the charges around to create the voltage. Therefore Work = integral from 0 to Q of V(q) dq = integral from 0 to Q...

Does the equation http://m.imgur.com/2KAADas Accurately describe the potential energy gained by an object falling by 100,000 units? I asked my physics teacher and he said he didn't know enough about integrals to answer it. I asked my math teacher and she just asked "Are you trying to find the...

Homework Statement An 18.5kg box is slid up a 5.6m long ramp that makes an angle of 33 degrees with the floor. What is the gravitational potential energy of the box relative to the floor? Homework Equations Ek = 1/2mv2 The Attempt at a Solution My teacher gave me an answer of 550J, but I'm...

Homework Statement Three electrons form an equilateral triangle 0.800 nm on each side. A proton is at the center of the triangle. Homework Equations U = k[(q_1*q_2)/r] The Attempt at a Solution I tried to use the following equation: k*[(3e^2)/(0.8*10^-9) - (3e^2)/(0.4*10^-9)] I plugged in...

Homework Statement A) An object moving along the x-axis is acted upon by a force Fx that varies with position as shown. How much work is done by this force as the object moves from x = 2 m to x = 8 m? B) A 50-kg child riding a Ferris wheel (radius of wheel R = 10 m) travels in a vertical...

Hello If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and B having different temperature: A: having only internal potential energy and B having...

Homework Statement 2 concentric shells are placed with inner shell having charge q and outer charge -q, with radii a and b respectively. Homework Equations don't know The Attempt at a Solution the question asked me to find self energy of the 2 shells and interaction potential energy,i found...

Homework Statement Find the potential energy function for the three mass, earth, and pulley system as shown. The potential energy will be as a function of the vertical position downward as shown in the diagram. Also, find the equilibrium position of this system. The two outside masses are...

Homework Statement Is the potential energy between atoms in solids, liquids and gases, elastic or electrical? I've read in some sources that for solids, p.e. > k.e. because it has the strongest intermolecular forces among the three states of matter. So I'm assuming it is elastic potential...

Homework Statement Why is potential energy variation between two points equals to the work of the opposite of conservative forces between these two points? Homework Equations If we call these forces $$\vec F_ext^C$$ \begin{equation} \Delta E_p=E_p(B)-E_p(A)=-\sum W_{A\rightarrow B}(\vec...

Note: I know this question has been asked before, but I wasn't allowed to ask my question on that thread 1. Homework Statement The gravitational self potential energy of a solid ball of mass density ρ and radius R is E. What is the gravitational self potential energy of a ball of mass density...

Science fair help needed! Horses use the energy stored in their tendons to help propel them over a jump- much like a spring. By determining the spring constant for the leg, the student wants to then calculate the potential energy stored in that leg. Would this work? From her research...

Homework Statement There are two concentric shells of radii a and b respectively ,inner shell has charge Q and outer shell is neutral what will be potential energy of outer shell due to inner shell Homework Equations ##V##=##\frac{KQ}{R}## PE=Charge .V The Attempt at a Solution I know what...

in shm,if minimum potential energy of an shm is not zero,does that mean that in mean position ,spring is stretched. eg mass attached to a vertical spring.

The motivation for this post comes from a discussion on another thread https://www.physicsforums.com/threads/questions-regarding-mass-volume-x-density.851172/ It seems worthwhile to me to try a simplification in this post to hopefully avoid the complications raised in the cited thread. Assume...

Hi everyone I'm kinda new here, your support will really be appreciated ! :D 1. Homework Statement Let's say the cylinder has radius R, and height T. Homework Equations U = ∫GmdM/x The Attempt at a Solution My attempt is shown in the picture, I took a tiny element of the cylinder with...

I present the following problem to my AP and have received a variety of answers, being a new physics teacher I am not sure that my answer is correct. I would love to see the solution and justification. Thanks One attempt based on the inference that one block is gaining U (A) and the...

I'm working on a homework problem which states: "Some object, starting from far down the negative x-axis and moving in the positive x direction, experiences a force, the potential energy U of which is modeled by the function U = 2e^(-x^2), where x is in meters and U is in Joules. The total...

Hello, I have this problem statement : "Due to air drag, the radius of a satellite’s circular orbit decreases from r to r - △r, where the positive quantity △r is much less than r. The mass of the satellite is m. Show that the increase in orbital speed is △v = +(△r/2)[(GM/r^3)^1/2]; that the...

Homework Statement A 0.50-kg object is attached to an ideal massless spring of spring constant 20 N/m along a horizontal, frictionless surface. The object oscillates in simple harmonic motion and has a speed of 1.5 m/s at the equilibrium position. (a) What is the amplitude of vibration? (b) At...

I am looking for a simple number which is the potential energy that can be stored in rubber. ( Joules per gram or something similar ) I know there are a number of forms of rubber and I keep reading numerous articles on how to calculate the energy content of a rubber band. Can anyone just tell...

Homework Statement A stone of mass 0.2kg is dropped from the top of a building 80m high. After t seconds it has fallen x meters and has a velocity of v. What is the potential energy of the stone t seconds later Homework Equations The answer is 2(80 - x) = 160 - 10t^2 Using suvat: s = ut +...