1
vote
0answers
27 views

What is the fluctuations of the energy of a simple harmonic oscillator? [on hold]

$$\begin{align} \varepsilon&=\frac{\vec{p}^{\,2}}{2m}+\frac{K}{m}\vec{q}^{\,2}\\ \rho(q,p)&=\biggl(\frac{\omega}{2\pi k_BT}\biggr)^3e^{-\frac{\varepsilon}{k_bT}} \end{align}$$ where ...
-1
votes
1answer
25 views

Spring launches a mass on an incline plane with friction, find the height [closed]

So I've calculated the answer to this problem, but my answer is different from my book's, so I'm trying to find the error. A spring with coefficient $k=600N/m$ launches a mass of $1.2kg$ from an ...
0
votes
1answer
30 views

Alignment of a system in equilibrium and its potential energy

Consider a flexible free conductor which is placed near a strong long bar magnet. How will the the conductor arrange itself if current is passed through it? I asked my professor: he gave me a hint ...
2
votes
1answer
155 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
3
votes
1answer
59 views

Why do safety helmets have a softer inner layer nearer the head?

I know that when an object collides onto the helmet, it causes an inelastic collision so that energy is absorbed by the structure of the helmet, so what exactly does the softer inner layer do? Does it ...
2
votes
4answers
78 views

Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
0
votes
0answers
49 views

Does a rotating plank only acquire rotational kinetic energy?

I have another doubt with a Kleppner problem :(. A thin plank of mass M and length l is pivoted at one end. The plank is released at 60$^{\circ}$ from the vertical. What is the magnitude and ...
-1
votes
1answer
24 views

Calculate amount of energy based on height of object

How can you calculate the amount of energy an object produces that falls from a particular height? Or water. In an eg i would like to know how can you calculate the amount of electricity water can ...
1
vote
1answer
28 views

How to calculate required energy to displace a pendulum?

How can one calculate the amount of energy needed to displace pendulum with given mass m and string length L to $\alpha$ degrees from resting position when acceleration due to gravity is known?
0
votes
3answers
48 views

Kinetic energy relationships with momentum and mass [closed]

If I have some arbitrary particle, we will call particle 1 and another particle 2 that have the same momentum, yet particle 1 has half the mass of particle 2, how does the kinetic energy compare ...
0
votes
1answer
47 views

How do you calculate the energy output if you know the volts, amps and time? [closed]

How do you calculate the energy output if you know the volts, amps and time?
0
votes
1answer
259 views

What is the difference between a pulse and a wave?

I wanted to ask what is the difference between a pulse and a wave. According to the definitions of them , they are almost the same. In the websites I looked at , the difference between them was ...
0
votes
3answers
108 views

Energy Required To Push Up a Slope

I'm having a bit of trouble with this problem: A $5.0\:\text{kg}$ block is moved up a slope with constant velocity of $2.5\:\text{m/s}$. The amount of force required to push the block up the slope is ...
1
vote
2answers
55 views

Kinetic energy of a mass rotating about two axes

I'm working on a question where I have to find an equation for the kinetic energy of a mass being rotated by a fold-able arm. The equation for $m_1$ is obvious, however, the equation I derived for ...
2
votes
0answers
40 views

De-excitation and vibrational frequency

By utilising energetic beams of particles it is possible to set atomic nuclei into vibration. For a certain nucleus the subsequent de-excitation results in the emission of photons of energy $1$ $MeV$. ...
0
votes
1answer
41 views

modern physics :emission spectrum [closed]

If in a hydrogen atom all possible transactions take place. The ratio of maximum frequency to minimum frequency is 135/7.what is the principal quantum number of excited state. The max frequency case ...
0
votes
0answers
22 views

Is this how I find the rate of change of internal energy for filling a vessel?

If I am filling a tank with something (lets say air) and both its volume and pressure are changing with time (It's not rigid), it it safe for me to say: $$u=h-Pv$$ ...
0
votes
1answer
90 views

Escape velocity problem

I was given a problem at school: How much Energy do we need to make a rocket of mass $m$ faster than the escape velocity so that it can travel in outer space? Here's how I worked: I know that ...
8
votes
3answers
812 views

Number of planks required to stop the bullet [closed]

A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be? Logically, to me the answer seems to be infinity, as always a ...
0
votes
1answer
61 views

What can cause a change in wave's shape - One dimensional wave

what can cause a change in wave's shape of one dimensional wave moving through a rope? It's velocity ? or the wave's length ? What can cause him change his shape.
15
votes
3answers
676 views

What happens in a car crash?

My mom and I were in a car accident. We are ok, but I want to know how fast the car that hit us was going. We were stopped at a light. The car that hit us from behind was a big GMC SUV. Our car was a ...
0
votes
1answer
54 views

Thermal resistance of thermal interface materials?

Thermal conductivity are often used for surfaces between the computer chip and the heat sink to increase heat transfer and they want high thermal conductivity to decrease the thermal resistance. By ...
1
vote
1answer
54 views

Work done (by gravity) on paired blocks [closed]

Why does gravity do more work on the block going down? The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?
0
votes
2answers
96 views

Potential energy of an infinitesimal length of elastic rod

I am having an embarrassingly hard time with the derivation for the potential energy of an infinitesimal element of an elastic rod of area A. The picture shown below is an element of the rod that has ...
0
votes
2answers
79 views

Conservation of Mass, Momentum and Energy - Airburst Rounds

I have a airburst round with set amount of fragments with a certain shape inside my bullet. After a certain distance has travelled, a charge explodes in the back of the round disintegrating the shell ...
1
vote
1answer
70 views

Work-Energy-Power Relations

A wind-powered generator converts wind energy into electrical energy. Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy. ...
0
votes
0answers
92 views

Determine pipe outlet temperature without length?

Let's say I am flowing a fluid through a pipe that has a constant surface temperature. Is it possible to determine the heat flux on the inner surface without knowing the pipe's length when the only ...
2
votes
0answers
78 views

Finding internal energy using equation of state

I have an equation of state as a function of $p$ (pressure), $T$ (temperature) and $V$ (volume) for a real gas and need to find an expression for the internal energy $U$. I know this is given by the ...
3
votes
0answers
157 views

Practice AP Physics B Exam Question regarding Momentum

I am trying to review momentum for the AP exam coming up. I will be taking the AP Physics C exam for Mechanics, but I was just practicing on any free response questions I could find and I came across ...
0
votes
2answers
227 views

Energy transfer in elastic collision [duplicate]

In a given reference frame where object 1 (with known mass and velocity) collides elastically with object 2 (with known mass and velocity), can we identify which object loses kinetic energy? Is it ...
0
votes
1answer
85 views

Rigid body problem

I have some doubts about the next excercise: A bar of length $2a$ and mass $m$ moves freely with both of its extremes on a ring of radius $\sqrt2a$. The ring can rotate freely in a certain ...
1
vote
0answers
69 views

Helmholtz free energy minimization using Lagrange [closed]

can you please help me with that one: Minimize free energy for a liquid crystal: $F = \int (K_{11} (div(n))^2 + K_{22} (n*rot(n) + q)^2 + K_{33} (n*rot(n))^2 ) dV$ in the case $n = cos(\alpha)*e_z ...
4
votes
1answer
170 views

Virial theorem and variational method: an exercise (re-edited)

I have a hydrogen atom, knowing that its Hamiltonian has been modified turning the standard potential $$ V_{0}(r) = -\frac{Z}{r} $$ into $$ V(r) = -\frac{g}{r^{\frac{3}{2}}} $$ with $g$ a positive ...
1
vote
1answer
190 views

Energy and time evolution of a particle in a potential well

Hoping this is not a silly and stupid question let me ask for help in this problem. I have a particle in an infinite square well (the box is from 0 to a), in the state described by the function ...
0
votes
1answer
56 views

Question about energy [closed]

Tom, weighted 60kg, set a world record of bunjee jumping, he jumped off at 223m height, and reached the lowest point when he's 50m above ground. If 30% of mechanical energy was lost when the cord was ...
2
votes
1answer
90 views

Speed of three objects falling with different masses

The following is the problem that I am working on. Three different objects each with mass $m_1<m_2<m_3$ is launched from the same height $h$ with three different angles $\theta_1 < ...
3
votes
2answers
120 views

Braking force required to allow bike to move down slope with an arbitrary constant velocity

Find the braking force required to allow a bike to move down a frictionless slope, inclined at $\theta$ radians above horizontal, with a constant velocity of v m/s. I'm confused because Newton's ...
0
votes
2answers
55 views

Yearly onshore wind turbine energy production [closed]

I am trying to work out the yearly energy production of an onshore Siemens SWT-3.0-101, hub height 94m, total height 144,5. Here is the power curve at each wind speed level worked out through a ...
-4
votes
2answers
269 views

Alternative derivation for the capacitor energy equation [closed]

I hope this is the right place for this kind of post. A friend is trying to derive the equation for the energy stored in a capacitor by analysing the change in potential on one plate when the ...
1
vote
3answers
158 views

A satellite in orbit fires it's engines for a short interval. Is the new orbit closer or further away?

A satellite is in a circular orbit when its engines turn on to exert a small force in the direction of the velocity for a short time interval. Is the new orbit further or closer to the Earth? The ...
0
votes
1answer
212 views

Muon 3 Body Decay

I'm trying to calculate the maximum energy of the electron in the decay muon >electron + electronantineutrino +muonneutrino in the reference frame of the muon having no kinetic energy. $m_m$=mass of ...
0
votes
1answer
322 views

Physics transformation energy [closed]

A 15kg child slides down a 2.3m -high playground slide. She starts from rest, and her speed at the bottom is 2.1m/s . What is the change in the thermal energy of the slide and the seat of her pants? ...
0
votes
2answers
479 views

How do I express the interaction energy between two charged spheres?

Consider two identical insulating spheres each with radius $R$ and uniform charge $Q$ through their volume. They are separated from their centers by a distance of $d>2R$. Here is my general ...
0
votes
1answer
564 views

Solve a problem of work and energy

A man pulling sled of his daughter by a massless rope, climbing a snowy hill whose slope is equal to 15 °. Considering that the mass of the sled is $4Kg$, the girl's $26Kg$ and $\mu _c = 0,25$, ...
1
vote
1answer
1k views

Where does the energy of a light bulb come from?

Where does the energy of a light bulb come from? Is it from the coil of wire, magnet in the generator, mechanical input to the generator or plug where the generator is connected to the wall?
0
votes
1answer
147 views

Antimatter collision - Energy Released

I think it's about time for me to ask this question, as I've been contemplating this for a while. $$E = mc^2.$$ This is Einstein's most famous equation. But what does it mean? On my own, I had to ...
3
votes
5answers
367 views

Ball rolling into a bowl - where is its maximum KE (speed)… given there is friction. See diagram

Please examine this diagram and answer the apparently trivial questions. I am particularly interested in reasoned answers for part (a)(ii) - where is the maximum Kinetic energy? I say it is at B ...
1
vote
1answer
54 views

Minimum energy for turning over a cube [closed]

This is a strange question from the physics Olympiade I wish to get some explanation for: Using a certain type of wood, cubes are sawn with different edge lengths $R$. When they are on the ground, ...
2
votes
2answers
2k views

Expression of kinetic energy in polar coordinates

Expression for kinetic energy in Cartesian coordinate: Expression for kinetic energy in polar coordinate (applying the transformation of coordinates): Why can't we express it in the following ...
0
votes
1answer
63 views

Energy spent by motor in a period

Consider a single coil that is turning in a constant and uniform magnetic field thanks to a motor. The normal to the coil is given by: $${\bf u}(t)=\sin (\omega t){\bf u_x}+\cos(\omega t){\bf u_z}$$ ...