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.
4
votes
1answer
355 views
Plotting a SHO in matlab
I have no prior experience of using matlab. My teacher want me to solve this question. I have been trying for a couple of hours now with no luck, please help!
The mass of 100 g hanging in a spring ...
1
vote
1answer
580 views
What makes zinc reactive?
What makes zinc so desperate to give up its electrons? Silver has one extra electron, and zinc has two, but why is zinc more reactive?
2
votes
2answers
637 views
Electric field at a point from a square surface
I'm trying to determine the electric field at a point P (located on the +Z axis) due to a square of side length [L] and centered at the x-y plane origin. The square has a constant surface density [s]. ...
1
vote
1answer
296 views
Mass fixed to a wheel - mechanics problem
I am struggling with a problem from classical mechanics. Imagine a massless wheel (to make it simpler) with a mass $m$ fixed to it rolling without slipping on a horizontal ground. If we now try to ...
1
vote
2answers
289 views
Finding $\psi(x)$ from Fourier modes
In quantum physics we've defined:
$$ \psi (x) = \sqrt{ \dfrac{1}{2 \pi \hbar} } \int^{ \infty }_{-\infty } \phi (p) \exp \left( i \dfrac{px}{ \hbar} \right) dp $$
Now,
$$a(k) \equiv \sqrt{ \hbar } ...
0
votes
1answer
458 views
Proving Operator identities (Quantum Physics)
How would I go about showing:
$$\hat{A}^{\dagger} + \hat{B}^{\dagger} = \left( \hat{A} + \hat{B} \right) ^{\dagger}$$
2
votes
2answers
349 views
Forces on a simple flat slope
This diagram is of a block (b) moving down a ramp unaided.
Taking gravity (g) as $9.8ms^{-2}$, and the mass of the block (b) as $0.2kg$, how can I find the force acting along the slope (f).
BTW: ...
1
vote
2answers
204 views
What is the possible potential?
The professor asked us to do this one:
"..Determine all potentials $V(r,\theta, \phi)$ for which it is possible for find solutions of the time independent Schrodinger equation which are also ...
2
votes
1answer
2k views
How to solve this Schrödinger equation?
I am taking an intro level quantum mechanics class. Our textbook gives a problem like this:
The deuteron is a nucleus of "heavy hydrogen" consisting of one proton and one neutron. As a simple ...
3
votes
1answer
353 views
Hydrostatic equilibrium of a star - simplification math error
I am trying to do this question and getting stuck at interpreting what the question is asking for.
$$dP/dR = -g(R)\rho(R) = -[GM(<R)/R^2]\rho(R).$$
Thus when we descend a distance $\Delta R$ ...
-1
votes
1answer
326 views
How does mass relate to resistance (Ohm's Law)
How can I relate mg to R?
Just to give you a scenario: If a free hanging weight was tied to a motor... I know the voltage (V) and current (I) so I can use V = IR to find R. What if I reduce the ...
4
votes
1answer
336 views
Electric Potential
A nonuniform linear charge distribution given by λ = bx, where b is a constant, is located along an x axis from x = 0 to x = L. What is the electric potential at a point on the y axis? Set potential ...
0
votes
2answers
1k views
Projectile motion without air resistance
Does the mass of projectile affect its trajectory when it is projected in no air resistance environment and why?
2
votes
1answer
136 views
Identifying unrealistic traits of this exoplanet. There are a few obvious ones, but I cant find them all. Help! [closed]
I need to find the inaccuracies of this computer generated picture, the picture shows a non existent exoplanet. I need to identify the unrealistic features of the planet and its surroundings and write ...
1
vote
2answers
215 views
Simple kinematics excercise, throwing something upwards
I am trying to solve this simple excercise:
Question
You throw a small coin upwards with $4 \frac{m}{s}$ . How much time does it need to reach the height of $0.5 m$ ? Why do we get two results?
...
0
votes
1answer
172 views
Standing Wave: How to show that $\frac{\mathrm df}{f}=0.5\frac{\mathrm dF}{F}$ where $f$ is frequency and $F$ is tension of the string?
How to do this?
Show that if the tension $F$ in a string is changed by a small amount $\mathrm dF$, the fractional change in frequency of a standing wave, $\frac{\mathrm df}{f}$ is given by:
...
2
votes
2answers
227 views
Calculating the deflection of an arbitrary beam of light from a thin lens
Suppose we have a lens with known focal length and are using the thin lens approximation. Is it possible to determine how an arbitrary beam of light will be deflected by it? Or, is it the case that ...
2
votes
0answers
647 views
Measuring the spring constant in a system with hydrostatic buoyancy
I have a physics lab tomorrow and I would appreciate it if you could give me your opinion on whether my reasoning is correct for this situation or not:
http://i.stack.imgur.com/WMzA7.jpg
The title ...
8
votes
9answers
6k views
What's the core difference between the electric and magnetic forces?
I require only a simple answer. One sentence is enough... (It's for high school physics)
1
vote
1answer
484 views
converting force from spherical to Cartesian coords
So I am working on my assignment, and have a question about converting coordinates. I dont know whether I should ask here or the math SE, so lets give it a try here.
The force in question is ...
0
votes
1answer
290 views
Angular momentum
I'm given with the following problem - it's an easy one, but it's nearly 1AM, I'm tired and I need some push into the general direction to get the solution:
A particle is assumed to be in the state
...
5
votes
3answers
3k views
Weight on carpet vs. hard floor
Will the scale say I weigh more, less, or the same on a carpet as compared to a hard floor?
You can assume the scale works via spring mechanism. Free body diagrams encouraged!
0
votes
3answers
554 views
Impulse - distance question
What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ?
Thanks!
Update 14.02.2011:
I still wasn't able to find an answer to this. ...
1
vote
1answer
2k views
Finding the steady state solution of a damped oscillator
A damped harmonic oscillator with
$m = 10$kg, $k = 250$N/m, and
$c = 60$kg/s is subject to a driving force given by $F_0\cos(\omega t)$,
where
$F_0 = 48$N.
(a) What value of ...
2
votes
2answers
531 views
Electric potential in a capacitor
Im a writing a school report regarding the electric energy and potential of a capacitor.
In short:
An experiment was carried out where we charged a capacitor, and then decharged it with an electric ...
1
vote
2answers
758 views
How long does it take a block to slide up and down a plane with friction?
So I am studying for my exam on monday for analytical mechanics. I am kind of stuck on a question, so wondering if someone can give me a pointer. I am actually looking for some pointers and some ...
0
votes
2answers
392 views
Understanding weight on an inclined plane
I'm trying to solve a problem where I have an object resting on an inclined plane, with the angle of the plan being alpha, and the weight being w. I'm having trouble figuring out how I can calculate ...
0
votes
3answers
1k views
Vector product in 2 dimensions [closed]
If I have a vector A=4i+3j and B=5i-2j, how can I find the vector product AxB? I know that given the angle, its C=AB sin theta, but how can I solve this without the angle?
2
votes
2answers
378 views
Homework about spinning top
I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 ...
1
vote
1answer
200 views
Top spun up with string under tension problem [duplicate]
Possible Duplicate:
Homework about spinning top
I have a top with an unknown mass. It has a moment of inertia of 4.00 * 10^-7 kgm^2
a string is wrapped around the top and pulls it so that ...
2
votes
3answers
1k views
Torque homework
We have learned that Torque is equal to a force that is perpendicular to a radius (displacement); however, I just cannot grasp one of the study questions we received:
A hammer thrower accelerates ...
0
votes
1answer
2k views
Electric Field for a hollow sphere with point charge
I think I am over thinking this question: A point charge of -2 microC is located in the center of a hollow sphere. The internal and external radius of the sphere is given by 6.5 and 9.5 cm, the charge ...
1
vote
5answers
478 views
Conserved quantities in generalized n-body problem
Given a collection of point-particles, interacting through an attractive force $\sim \frac{1}{r^2}$.
Knowing only $m_1a=\sum_i \frac{Gm_1m_i}{r^2}$ and initial conditions we can deduce the motion of ...
0
votes
2answers
2k views
Homework Help - Physics / Calculus III / Force-Work Problem
I have tried to answer the problem correctly, and I have found similar (and even an identical) problem in my textbook, yet I still can't seem to yield the correct answer with this specific problem.
...
0
votes
2answers
577 views
Mechanical energy problem
Question goes: "An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.6 m above its equilibrium position. It then swings to its lowermost point ...
0
votes
4answers
196 views
Calculating electric field
This problem is giving me a lot of problems. So $E=k*q/d^2$. We'd want to find the distance from q1 to P, which is .1 meters (not cm) using pythagorean thereom. So we know k, which is just $9x10^9$ ...
6
votes
3answers
1k views
Charge density in concentric spheres
Question:
If there are two conducting spherical shells and the inner shell is grounded, what will be >the charge density in the inner shell if there is a charge Q placed on the outer shell?
...
1
vote
2answers
1k views
Transfer function of an RLC circuit
I'm trying to simulate an RLC circuit using transfer function. Circuit is there: http://i.stack.imgur.com/MC8ME.png (I'm a new user therefore I cannot post images)
But I can, L.Motl...
Main ...
0
votes
4answers
823 views
When is the force null between parallel conducting wires?
Consider two long wire with negligible resistance closed at one end of the resistance R (say a light bulb), and the other end connected to a battery (DC voltage). Cross-sectional radius of each wire ...
3
votes
2answers
1k views
How to calculate cord tension in a vertical circle?
Mass m is connected to the end of a cord at length R above its rotational axis (the axis is parallel to the horizon, the position of the mass is perpendicular to the horizon). It is given an initial ...
0
votes
2answers
530 views
Space state equation for RLC to calc voltage on resistor and capicitor [closed]
I have some task to do:
Please write equations in Simulink and
simulate the circuit elements
connected in series RLC (it was the
electrical!). Outputs of the system
should be voltage on ...
1
vote
1answer
1k views
Solving straight-line motion question for time
I apologise in advance if this question doesn't appeal to the advanced questions being asked in this Physics forum, but I'm a great fan of the Stack Exchange software and would trust the answers ...
1
vote
1answer
576 views
Electron/Photon Scattering
Hey guys,
I have a final tomorrow and I am going over some assignments. One of the questions from the assignment was:
A photon having 37 keV scatters from a
free electron at rest. What is the
...
2
votes
2answers
480 views
Does the cube stay on the loop-de-loop?
Suppose a cube of mass $m$ enters a loop-de-loop of radius $r$, travelling halfway around and reaching the top. At the top, it has velocity $v$, and the second half of the loop is frictionless.
How ...
0
votes
2answers
2k views
Spectral Line Width and Uncertainty principle
so I've been at this for about 3 - 4 hours now. It is an homework assignment (well part of a question which i've already completed). We did not learn this in class. All work is shown below.
An ...
2
votes
2answers
346 views
How will you fix the direction of the lines of force due to circular current?
I have tried to learn it myself but I was unable to understand. Can you please explain it in detaails with simple example.
Thanks
-1
votes
3answers
2k views
photoelectric effect
A 1.0 mW laser ($\lambda$ = 590 nm) shines on a cesium photocathode (ϕ = 1.95 eV). Assume an efficiency of $10^{-5}$ for producing photoelectrons (that is, 1 photoelectron is produced for every 10^5 ...
-5
votes
1answer
146 views
Amount of 2 amperage [closed]
I have 2 equation describing the alternating amperage i1 and i2. I need to get amount of these amperages.
My equations:
i1= 10 sin (ωt+30)
i2= 20 sin (ωt-50)
...
0
votes
3answers
679 views
4th equation of motion
Ive been given the 4 equations of motions The fourth being:
$$s=ut+\frac{1}{2}at^2$$
If rearranged it forms the quadratic equation
$$at^2+2ut-2s=0$$
But that means that t has 2 values.
Will ...
0
votes
3answers
3k views
Period of Precession
I'm trying to find the period of precession for a gyroscope. Now I was able to find the angular precession rate, which was 1.132 rad/s, but I have no idea how to convert this to a 'period', and google ...
