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. Please READ THE GUIDANCE IN META before asking homework questions.

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2answers
79 views

How to convert RL Circuits? [closed]

How do we convert a parallel RL circuit into its equivalent series RL circuit ?
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votes
1answer
118 views

Charge of electrons and protons

I have a question which reads: "A conductor has a charge of $9.6 * (10)^{-19}$ coulomb. The conductor will have- " The problem I face in this question is due to not knowing the exact value of ...
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votes
2answers
275 views

Why is static friction called self adjusting force? [closed]

Explain what is limiting force of static friction.
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votes
1answer
44 views

Determining distance from object in concave lens [closed]

so I was studying for my Yr11 Physics test tomorrow and I came across a question that I got the wrong answer on, all of my friends are getting the same answer. Question: You wish to project the image ...
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votes
1answer
40 views

Scalar Field of a long thin wire

Given the situation that $B=-\nabla A$ where B is magnetic field and A is some Scalar Field. How can I calculate the scalar field, A. We are dealing with current free region, here. I know we can ...
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votes
2answers
118 views

Harmonic Motion [closed]

A light elastic string is stretched between two points, one lying vertically below the other. A particle is attached to the midpoint of the string, causing it to sink a distance h. Assuming that the ...
-1
votes
1answer
185 views

Can you help me with physics lab calculations? [closed]

My question is, how do you find the torque of a rotating spool with a connected string being pulled down by its hanging mass? So in this experiment we had a machine with two rotating discs, one on ...
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votes
1answer
59 views

Centripetal acceleration and gravitational acceleration on a thread [closed]

This is a question from my physics textbook. "A $200$ gram weight is suspended in a $2.5m$ long thread in the roof. The weight is pulled out sideways, creating the angle $\alpha$ and is then ...
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votes
2answers
384 views

Calculate the acceleration of a moving elevator [closed]

An elevator is moving down with uniform acceleration. A man inside the elevator who wants to measure the acceleration drops a coin as soon as the elevator starts. The coin is 6ft above the floor of ...
-1
votes
2answers
111 views

Vectors question? [closed]

I am stuck on this vectors question I have for home work. Does anything think they can help point me in the right direction on how to solve this? An explorer is caught in a whiteout (in which the ...
-1
votes
1answer
346 views

Electric circuit question [closed]

http://www.fisme.uu.nl/nno/opgaven/bestanden/Ronde1-Theorie-2009.pdf, question 5: You have to calculate Id when the switch at S is opened, when its closed, the Id = 0.5 A. All resistors are ...
-1
votes
1answer
181 views

Normalizing a Wave Function

How would I normalize the wave function: $ \psi (x)$ = $Ce^{i\rho_0x/\hbar}e^{-|x|/2\Delta x}$? I squared it, which got rid of the imaginary part-Then I considered breaking up the absolute value-but ...
-1
votes
1answer
95 views

Lunar and solar tides [closed]

I just read the following statement in a book: If the diameter of the earth increased by 20%, both lunar and solar tides would be weakened with lunar tides weakening more than solar tides. What ...
-1
votes
1answer
371 views

Kinetic energy of a rotating rod [closed]

I have no idea where to even begin with this... Find the kinetic energy of a record of uniform density, mass 50 gm and radius 10 cm rotating at 33 and 1/3 revolutions per minute. Normally I would ...
-1
votes
1answer
100 views

Are the forces I'm using correct? (ball in air) [closed]

I have been working on a program which should simulate all the forces on a spherical object. Right now those are balls, but they can easily be changed to something else. These are the formulas I use ...
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votes
1answer
104 views

Expressing a force in components [closed]

If there is an object on some ramp, how do I express its weight in terms of vectors orthogonal and parallel to the ramp surface? For example, if the object has a weight $\vec W=m\vec g$, then how do ...
-1
votes
1answer
192 views

Eigenvalue of Optical waveguide [closed]

Consider you have a slab waveguide having n1=3.5 and n2=1.45. The value of critical angel is 24.5 degree approx. Similarly effective refractive index will be in between 1.45 and 3.5. How can we find ...
-1
votes
1answer
247 views

Problem from Sakurai about a delta-function potential [closed]

Can you help me with this problem from Sakurai: A particle of mass m in one dimension is bound to a fixed center by an attractive delta-function potential: $$V(x) ~= ~-a\delta(x) , \qquad ...
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votes
1answer
318 views

Understanding centripetal force vs frictional force diagrams?

I have an actual physics problem and also a conceptual question to go with it. From some test prep I was presented with this straight-forward question: What is the minimum radius that a cyclist can ...
-1
votes
1answer
166 views

Solving differential Equation for the Two-Body Problem

So, I'm following the derivation in D. Morin, Introduction to Classical Mechanics, of the equations for a two-body system. I understand all of it, aside from this one step. When he's talking about ...
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votes
1answer
64 views

Dynamic equation

I'm asked to give the dynamic equations of a charged particle moving on a potential, under relativistic considerations, basically $dp/dt$, with $p$ the 4-momentum vector. The question for the three ...
-1
votes
1answer
67 views

Calculate energy from an reaction [closed]

I'm trying to calculate the released energy from a reaction. The radioactive substance polonium decays according to this formula: $$^{210}_{84}\mbox{Po} \rightarrow \mbox{X}+^4_{2}\mbox{He} $$ At ...
-1
votes
1answer
248 views

Convert units from cal cm^-1 day^-1. to Wm-2

I am trying to calculate the energy budget of a water body and the last term I'm trying to calculate is the energy advected from the water body ($Q_v$). This equation is given by: $Q_v = V ( (T_1 - ...
-1
votes
2answers
110 views

Proof $\left[ {\hat H,{{\hat p}_i}} \right] = - \frac{\hbar }{i}\frac{{\partial \hat H}}{{\partial {{\hat q}_i}}}$ [closed]

I have a problem with the Hamiltonian, I don't think anything to solve it!! So could you give me some hints! Knowing that: $$\left[ {{{\hat p}_i},{{\hat q}_k}} \right] = \frac{\hbar }{i}{\delta ...
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votes
1answer
70 views

Charge gained due to photoelectric effect [closed]

Here I think, one beam will knock out just one electron. So, I am not able to even understand what the question says. Please someone give a hint as to what the question asks... As source of the ...
-1
votes
3answers
187 views

Impedance of a circuit [closed]

I am trying the following problem. A resistor with $295\Omega$ and an inductor are connected in series across an AC source that has voltage amplitude of $550V$. The rate at which electrical energy is ...
-1
votes
1answer
89 views

Differentiating a sinusoid [closed]

http://i.stack.imgur.com/ndLgm.png I don't see the how the author derived that $\frac { dv }{ dt } \leftrightarrow\overrightarrow { V } j\omega$.
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votes
1answer
914 views

Standing Waves: finding the number of antinodes [closed]

A string with a fixed frequency vibrator at one end forms a standing wave with 4 antinodes when under tension T1. When the tension is slowly increased, the standing wave disappears until tension T2 is ...
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votes
2answers
2k views

Work done by the air resistance [closed]

A ball of mass 0.37 kg is thrown upward along the vertical with a initial speed of 14 m / s, and reaches a maximum height of 8.4 m. a) What is the work done by air resistance on the ball? b) ...
-1
votes
2answers
233 views

Simple Vector Problem [closed]

I'm a bit stuck on a homework question that I've been assigned. The question is as follows: You are paddling a canoe at a speed of 4 km/h directly across a river that flows at 3 km/h. (a) What is ...
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votes
1answer
229 views

General Physics Short question [closed]

Does any one know where this formula come from ? $\alpha (t) = -\omega^2\ \Theta(t)$ Thanks
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votes
1answer
53 views

Is this $W_{r} = \frac{1}{2}kx^2 $ procedure correct [closed]

I have a $0.40 Kg$ of mass that has $v= 0.5 m/s$, and then crashes with a spring with constant $k = 750N/m$ Whats the distance that the spring was compressed? I was using the equation $W_{r} = ...
-1
votes
1answer
397 views

Internal forces in a truss and its geometry

I'm to work out the internal forces in a truss, but I can't get my head around the geometry of the truss itself. I'm starting to think there may have been information on the diagram which I missed. ...
-1
votes
3answers
1k views

A chain 64 meters long whose mass is 20 kilograms is hanging [closed]

A chain 64 meters long whose mass is 20 kilograms is hanging over the edge of a tall building and does not touch the ground. How much work is required to lift the top 3 meters of the chain to the top ...
-1
votes
1answer
228 views

Distance and displacement of an object on a straight line [closed]

I had this homework problem, but don't actually know if what I did is right, or that I even read the problem correctly. Can someone please tell me if this is the right interpretation of the problem ...
-1
votes
1answer
259 views

Properties of expectation values of quantum operators [closed]

$$\langle \hat A \rangle \langle \hat B \rangle=\langle \hat A\hat B \rangle,$$ $$\langle \hat A \rangle + \langle \hat B \rangle=\langle \hat A + \hat B \rangle,$$ $$\langle \hat A^2 \rangle ...
-1
votes
1answer
1k views

Mixing Water at Different Temperature

If I have cup of water at room temperature (say, $25^\circ$C). What would be the resultant temperature if I pour another cup of same amount of water at $100^\circ$C to it? Is it simply ...
-1
votes
1answer
140 views

How to find replacement function of a mass?

I wonder how I can find the replacement function of the center of the blue mass? The center of mass of the blue mass is $(0,0)$ and the blue mass is homogeneous. The masses do not move at t=0 in the ...
-1
votes
1answer
86 views

I think there is a mistake in solutions to this problem. plus and minus sign

! I pretty much had what the solutions had, but we disagreed with one thing, a minus sensitive sign. $\sum W = \Delta K$ $\int_0^{-s} - ks^2 ds = \frac{ks^3}{3} = \frac{1}{2}m(v^2-4^2)$ ...
-1
votes
1answer
571 views

How should I draw this free-body diagram?

The horizontal force P acts on the rim of the homogeneous cylinder of radius R and weight W. Determine the smallest coefficient of static friction that enables the cylinder to start rolling up the ...
-1
votes
2answers
3k views

Finding initial velocity using conservation of momentum and energy [closed]

A 14 g bullet is fired into a 120 g wooden block initially at rest on a horizontal surface. The acceleration of gravity is 9.8 m/s^2. After impact, the block slides 6.97 m before coming to rest. If ...
-1
votes
2answers
369 views

A proton is trapped in an infinitely deep well of L meters. The proton is in the first excited state. How does the excited state change the question.

The real question was: A proton is trapped in an infinitely deep well of 1*10^-14m. I suppose that is unimportant as that should only help us decided the limits of our integration. What I'm worried ...
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votes
1answer
557 views

How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates?

How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates? I use the identities $x=r\cos\phi$, $y=r\sin\phi$, and $r^2 = x^2 + y^2$, but I block at some point.
-1
votes
1answer
146 views

Radiation dosage problem [closed]

A large room is filled with air polluted with Caesium-137 at an average density of 1 Cs-137 particle per $\text{cm}^3$. A human is sitting inside the room for duration of $T$. What is the total energy ...
-1
votes
1answer
434 views

Acceleration Force [closed]

A 6500-kg helicopter accelerates upward at 0.60 m/s² while lifting a 1200-kg car. (a) What is the lift force exerted by the air on the rotors? (b) What is the tension in the cable (ignore its mass) ...
-1
votes
0answers
21 views

Runs of a vacuum pump? [on hold]

After how many runs of a vacuum pomp with volume $v$, the initial pressure $p_i$ of a balloon is reduced to a final pressure $p_f$? Baloon's volume is $V$ ($V>v$).
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votes
0answers
23 views

heat supplied by two heat source in reversible heat engine [on hold]

A reversible engine is supplied with heat from two reservoirs at 900 K and 600 K and rejects heat to a sink at 300 K. The engine develops work equivalent to 90kJ/s and rejects heat at the rate of 56 ...
-1
votes
0answers
15 views

Obtain the electric field [duplicate]

Let $V=(xyt^3T)j+(x^4tT)k$. Find the curl of the magnetic field and the electric field. The curl I found to be $-(4x^3t)j+(yt^3)k$ It's sensible to leave out the units T right? How do I find the ...
-1
votes
0answers
18 views

Mechanics Dynamics_Kinetics [on hold]

Figure shows an engine (e.g. IC engine, electric motor, turbine, etc.,) coupled to a load through a common shaft. The engine generates or supplies energy to the load, whereas the load absorbs the ...
-1
votes
0answers
23 views

Vectors-a tricky problem [duplicate]

A particle subjected to two equal forces along two different directions. If one of the forces is halved, the angle which the resultant makes with the other is also halved. The angle between the forces ...