Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright.
1
vote
3answers
267 views
Same momentum, different mass
The question is: if
A bowling ball and ping pong ball
are moving at same momentum
and you exert same force to stop each one
which will take a longer time? or some?
which will have a longer ...
1
vote
1answer
115 views
Lorentz transformations for sine wave in random direction
Hello i have been struggling to derive Lorentz transformations for a sine wave, which is traveling at random direction. I started by prooving that phase $\phi$ is invariant for relativity and that ...
2
votes
1answer
112 views
helium balloon tied to a car [closed]
A helium balloon is tied to the seat of a car. The doors and windows of the car is closed. If the car now starts moving, in which direction will the balloon move- front or back?
0
votes
1answer
336 views
Calculate the UPS Capacity in amp-hours [closed]
I am trying to find out the UPS capacity in amp-hours for my HP UPS system.
I've already done some calculations based on the UPS information from the HP Power Manager software.
Bellow are my ...
2
votes
2answers
147 views
Energy in electric field
I'm having some trouble understanding a homework question and would appreciate some help.
The question is as follows:
Jenny charges a capacitor with the help of a battery. She then removes
the ...
0
votes
2answers
241 views
How does one calculate the volume of a nucleus and the volume of an atom (in this case hydrogen)?
The hydrogen atom contains 1 proton and 1 electron. The radius of the proton is approximately 1.0 fm (femtometers), and the radius of the hydrogen atom is approximately 53 pm (picometers).
0
votes
1answer
59 views
1D Acoustical Relations beyond nearest neighbor couplings
Consider some 1D Lattice of atoms with nth neighbor coupling of strength k_{n}. I'm looking for the dispersion relation for acoustical phonons under these conditions.
I start with the Lagrangian,
...
1
vote
1answer
45 views
Rays in Symmetric Resonator
I'm having some trouble figuring out how to get started on this question:
If I have a symmetric resonator with two concave mirrors of radii $R$ separated by a certain distance, after how many round ...
0
votes
2answers
374 views
Deriving the Poynting Theorem
I am trying to derive the Poynting theorem. So far, I've only been able to narrow down which equations I think I'll need to do so. These are the equations:
Maxwell's Equations:
$$
\nabla\times{\bf E} ...
0
votes
0answers
74 views
How do I figure out the normal force on a person on an accelerating platform? [closed]
My question is an elaboration on this question: Force on rope with accelerating mass on pulley
The elaboration is to determine what the Force that the platform exerts on the person. Assume the ...
1
vote
1answer
164 views
Bouncing Ball Pattern
If a ball is simply dropped, each time a ball bounces, it's height decreases in what appears to be an exponential rate.
Let's suppose that the ball is thrown horizontally instead of being simply ...
1
vote
1answer
153 views
Questions regarding solving the Brachistochrone problem using Lagrangian
brachistochrone problem: Suppose that there is a rollercoaster. There is point 1 ($0,0$) and point 2 ($x_2, y_2)$. Point 1 is at the higher place when compared to the point 2, so the rollercoaster ...
0
votes
2answers
88 views
Proof of $T=\sqrt{2y/a}$ in uniformaly accelerating object [closed]
Suppose that there is a object that does a y-axis-only free fall to ground. The initial distance from the ground is defined as $H$.
How does one prove that time the object takes to reach the ground ...
0
votes
0answers
74 views
Describing the movement of the object in a particular situation in Lagrangian way
Suppose there is a object M, (sliding motion) moving by the initial speed $v$ and the initial location $x_0$. Otherwise noted, friction is assumed to be nonexistent. It then meets a circular mold ...
0
votes
2answers
127 views
Frequency of a tuning fork in a vacuum
Consider this equation of a damped harmonic oscillator such that:
$$
\ddot{x}+2\gamma\dot{x}+\omega^2_0=0
$$
with: $\gamma=\frac{b}{2m}$ and $\omega_0=\sqrt{\frac{k}{m}}$
Finally, we know that the ...
1
vote
1answer
375 views
Adiabatic expansion [closed]
I'll start off by saying this is homework, but I ask because I don't understand how the math should work (I don't just want an answer, I'd like an explanation if possible). I understand if this is ...
0
votes
1answer
1k views
Distribution of charge on a hollow metal sphere
A hollow metal sphere is electrically neutral (no excess
charge). A small amount of negative charge is suddenly
placed at one point P on this metal sphere. If we check on
this excess negative charge a ...
0
votes
0answers
36 views
What is some analogous experiment about the black holes by using the diary product like eggs, milk? [duplicate]
Possible Duplicate:
Black hole analog experiment?
I will explain my situation a little bit:
My teacher assign a experimental project that must be including the diary product: egg and milk ...
2
votes
1answer
171 views
A differential equation of Buckling Rod
I tried to solve a differential equation, but unfortunately got stuck at some point.
The problem is to solve the diff. eq. of hard clamped on both ends rod.
And the force compresses the rod at both ...
1
vote
2answers
494 views
Barrier in an infinite double well
I am stuck on a QM homework problem. The setup is this:
(To be clear, the potential in the left and rightmost regions is $0$ while the potential in the center region is $V_0$, and the wavefunction ...
2
votes
1answer
362 views
Schrödinger equation with complex potential
In 1 dimension what is the solution of the Schrödinger equation with potential
$$ V(x) = V_r + i V_i $$
Potentials are constant.
1
vote
2answers
304 views
Calculating force required to stop bungee jumper
Given that:
bungee jumper weighs 700N
jumps off from a height of 36m
needs to stop safely at 32m (4m above ground)
unstretched length of bungee cord is 25m
Whats the force required to stop the ...
3
votes
2answers
185 views
Does air resistance ever slow a particle down to zero velocity?
If a particle moves in a place with air resistance (but no other forces), will it ever reach a zero velocity in finite time? The air resistance is proportional to some power of velocity - $v^\alpha$, ...
4
votes
4answers
2k views
Infinitely charged wire and Differential form of Gauss' Law
I have tried calculating the potential of a charged wire the direct way. If lambda is the charge density of the wire, then I get
$$\phi(r) = \frac{\lambda}{4 \pi \epsilon_0 r} \int_{-\infty}^\infty ...
2
votes
2answers
1k views
Magnetic field in a cavity
We are given an infinitely long cylinder of radius $b$ with an empty cylinder (not coaxial) cut out of it, of radius $a$. The system carries a steady current (direction along the cylinders) of size ...
0
votes
0answers
39 views
Could you help and check my four easy dynamics tasks? [closed]
So I have four tasks to do and I have a guess for some of them but would greatly appreciate if you could help me be sure of it or clarify what I don't understand.
A car covers 2000m in 2 minutes and ...
0
votes
1answer
343 views
Satellite Orbital Period [closed]
I know I can calculate the period of a satellite orbit by Kepler's third law, but somehow it does not work out.
The sattelite is 20200km from surface of the earth.
$r=$orbits radius=earths ...
3
votes
1answer
127 views
Angular acceleration of stone disk
I have a conceputal question regarding the following problem:
A round massive stone disk with diameter $0.600 m$ has a mass of $50.0 kg$. The stone rotates at an angular velocity of $115.2 rad/s$, ...
0
votes
0answers
37 views
Off-center vortex
If we have a off-center vortex with strength $n$ in a superfluid contained in a cylindrical container (with distance $r$ away from center), the angular momentum is determined from the following ...
-1
votes
1answer
203 views
Hit a moving target [closed]
There is an object moving from $(X_1,Y_1)$ to $(X_2,Y_2)$ with speed of $V$. there is a third object in in $(X_3,Y_3)$.
now I want to hit the first object with the second one. and imagine that the ...
0
votes
1answer
1k views
Work Done by an Adiabatic Expansion
I am given the information that a parcel of air expands adiabatically (no exchange of heat between parcel and its surroundings) to five times its original volume, and its initial temperature is 20° C. ...
2
votes
1answer
605 views
Work Done in an Isobaric Process
I am given the information that an air parcel undergoes isobaric heating from 0° C to 20° C, and that's all I'm given. I have to determine the work done by the parcel on its surroundings. I know that ...
3
votes
1answer
163 views
Lab observation correct? As distance decreases, velocity increases, stderr decreases
The experiment goes like this:
Allow a moving cart to move from the top of an incline plane ($x_0$) downwards. The time taken will be recorded by the picket fence (those things you see wired up). ...
1
vote
1answer
216 views
Is it possible to prove that the curl of a gradient equals zero in this way?
If $(\nabla\times\nabla\Phi)_i = \epsilon_{ijk}\partial_j\partial_k\Phi$, where Einstein summation is being used to find the $i$th component...
Using Clairaut's theorem $\partial_{i}\partial_{j}\Phi ...
4
votes
1answer
940 views
Shouldn't the electric field in a solid insulating sphere be linear with radius?
I am a senior in High School who is taking the course AP Physics Electricity and Magnetism.
I was studying Gauss's laws and I found this problem:
A solid insulating sphere of radius R contains a ...
0
votes
1answer
304 views
Simple derivation of the tension of a cord on a suspended mass
Just wanted to disclaim this problem -- it is homework. However, I am not asking for the solution, I am wondering if anyone can tell me what I may be doing wrong in solving this specific tension ...
0
votes
0answers
399 views
Conceptual questions in Randall D. Knight- Physics for scientist and engineers [closed]
Where can one get answers for conceptual questions in book Physics for scientist and engineers by Randall D. Knight?
0
votes
0answers
61 views
Velocity of two-dimensional flow [closed]
If the velocity in a two-dimensional flow is given as $\vec u = \left\langle {u(y),v(y),0} \right\rangle$. Why must $v$ be constant? I am not sure where to start. Can anyone help?
-2
votes
1answer
114 views
A closed vessel full of water [closed]
A closed vessel full of water is rotating with constant angular velocity $\Omega$ about a horizontal axis. Show that the surfaces of equal pressure are circular cylinders whose common axis is at a ...
0
votes
0answers
93 views
Two-dimensional flow [closed]
Consider a two-dimensional flow $\vec u = \left\langle {u,v} \right\rangle$ of a Newtonian fluid with constant pressure and dynamic viscosity in a static container V with rigid walls S. Define the ...
0
votes
0answers
50 views
Energy equation [closed]
The energy equation for an ideal inviscid fluid is
$$\frac{d}{{dt}}\int_V {kdV = - \int_S {\left({\frac{p}{\rho } + gz + k} \right)\vec u \cdot \hat ndS}}$$
where $k = \frac{1}{2}\vec u \cdot \vec ...
0
votes
0answers
149 views
Velocity of flow in cylindrical coordinates [closed]
An infinitely long cylindrical bucket with radius $a$ is full of water and rotates with constant angular velocity $\Omega$ about its horizontal axis. The gravity is in the vertical direction. The ...
0
votes
0answers
54 views
Experimental Physics [closed]
A heater and thermocouple are used to measure and control the temp. T of a sample at $T_{0}=250^{o}C$. A feedback circuit supplies power P to the heater according to the equation $P=P_{0}+G(T_{0}-T)-D ...
0
votes
3answers
184 views
Classical mechanics. One-dimensional motion
Here is one task below.
How to solve equation
$$
m\ddot {x} + ax = F(t), x(0) = \dot x (0) = 0
$$
in quadratures by using two methods?
I tried to create a system of equations
$$
\begin{matrix} \dot ...
0
votes
0answers
192 views
What is the tension in the rope at that point? [closed]
A heavy ball with a weight of 120 is hung from the ceiling of a lecture hall on a 5.0--long rope. The ball is pulled to one side and released to swing as a pendulum, reaching a speed of 6.0 as it ...
1
vote
1answer
306 views
Electron Incident On A Finite Potential Barrier
This is problem 2.8.3 from Miller's Quantum Mechanics For Scientists And Engineers. I'm getting stuck when I try to figure out the wave equation on the right-hand side of the barrier. The original ...
0
votes
0answers
74 views
Which Element is reduced in this reaction? [closed]
This question has been reposted to the Chemistry StackExchange, and closed here. If you can answer it, please head over to the Chemistry site and answer it there.
Which element is reduced in ...
0
votes
0answers
50 views
Estimating the radius of the galaxy with trigonometry
It'd be my first question here. I've spent too much time trying to figure it out and I've decided that there must be something I've missed.
With the Tangential-Point Method (which is basic ...
3
votes
2answers
173 views
Find distance between turtles
I've been thinking about the following problem for some time now and was wondering if anyone could shed any light on it.
At time $t = 0$, turtle A sits at ...
0
votes
0answers
39 views
thermodynamic air turbine proble [closed]
can someone help me solve this problem?? Thank you soooooooooooo much!
An evacuated tank of 1 m3 is attached to the exhaust of an air-turbine-driven grinding wheel. Air at atmospheric pressure and ...
