# Tagged Questions

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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### Elementary physics question…requires calculus?

A 2500.0kg car is going at a constant velocity of 14.0 m/s and hits the breaks to stop. It skids 25m. What is the coefficient of friction of the tires to the ground? So I have acceleration = -4.0 ...
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### What does “along the handle of the cart” mean? And how does one calculate weight?

A horizontal force is used to pull a $5.0\text{ kg}$ cart at a constant speed of $5.0\text{ m/s}$ across the floor. The force of friction between the cart and the floor is $10\text{ N}$. ...
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### How can a block which is not receiving the direct force have a greater acceleration?

I solved it like this: $$F(\text{st max})=5\text{ N}$$ For the top block, \begin{align} 6\text{ N} - 5\text{ N} &= 1a \\ a &= 1\ \mathrm{m/s^2} \end{align} For the lower block, the ...
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### Find current in a nontrivial circuit

Let us assume that we have this circuit: We know that: $$I_1 = I_2 + I_3$$ $$I_1R_1 + I_3R_3 = V$$ $$I_1R_1 + I_2R_2 + \dfrac{q_c}{C_1} = V$$ Therefore we can write: $$I_1 = k_1 - k_2*q_c$$ ...
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### Problem Of Lazy Fish [closed]

Fish achieve neutral buoyancy (so they don't have to swim constantly to stay in place) via a swim bladder. A swim bladder is a little internal sack that they can inflate/deflate with air, which ...
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### Problem Of Pumping Rubber [closed]

One can work out by either lifting weights or using a tension band, which is like a big rubber band. If we model the rubber band as a big spring with spring constant $400 N/M$ how far in meters must I ...
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I would like to ask you about the separation of variables of the Dirac equation in curved space-time. The metric is given by $$ds^{2}=-dt^{2}+dr^{2}+r^{2}d\theta^{2}+\alpha^{2}r^{2}\sin^{2}\theta ... 0answers 716 views ### Time to travel distance given acceleration/deceleration [closed] A body accelerates at 0.2 m/s^2 & retards at 0.3 m/s^2. Maximum velocity obtained by it is 30 m/s. Find the least time in which it covers 6 km Well, if I do not assume that the body ... 1answer 143 views ### Force on a coil inside of a voice coil as a homework exercise we were given the following question: Given the following voice coil: With depth = 20 mm Permanent magnets with B = 1.23 T, Ur = 1.1 The coils has 20 turns, I = 1 Ampere. a) ... 5answers 306 views ### Current division in ideal inductors? The Question is:- Find the current distribution in the inductors at steady state (i.e. assuming t\rightarrow \infty after the switch is closed and circuit established and consider the ... 0answers 191 views ### Electric fields between 2 spheres with different voltages [closed] Consider two spheres, both with the same diameter. Case 1: sphere A is 100v, sphere B is 0v Case 2: sphere A is 50v, sphere B is -50v Which case has the higher electric field? Electric potential ... 0answers 33 views ### Gyrocompas equation Ok, need a little help for part (b) of the following problem. I set my axis similar to figure 113 and have expressed both \omega and \Omega in terms of the new coordinates. I have been told to ... 1answer 175 views ### Math / Physics Help - Barrel Pressure and Velocity Back in 1993 I derived the following equations to calculate projectile velocity and barrel pressure. Recently, I have noticed that I need to double the calculated results in order to obtain real word ... 0answers 169 views ### Lagrangian Dynamics Question [closed] Two equal masses of mass M are glued to a massless hoop of radius R is free to rotate about its center in a vertical plane. The angle between the masses is 2\theta. Find the frequency of ... 2answers 430 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 ... 1answer 109 views ### Lorentz transformation - need a little clarification So the question states: A's and B's systems are related by the standard Lorentz transform. B simultaneously fires off two photons from transmitters distance D apart along the x' axis, and in the ... 2answers 90 views ### Moment of Inertia [closed] Let f(x) = \frac{1}{L} be a probability function, where L is constant. Find the mean and variance. Discuss your results by making a connection to the moment of inertia definition. 1answer 57 views ### Gradient of the potential originated from two similar magnetic vector potentials is not the same The magnetic vector potential \textbf{A} can be defined up to a gradient of a field. Adding or subtracting such gradient should not change the physics of the problem. The same reasoning is applied ... 2answers 92 views ### can resistance be found without knowing length? is it possible to find to resistance without knowing the length? i am tryigng to solve a problem that requires me to find the resistance.I cant seem do so without knowing the length of the circuit ... 1answer 86 views ### Resistances in a circular loop I have no idea what formula I'm supposed to use.I just want to know the concept that would allow me to get the answer. I know basic concepts of electricity like charge, currents, etc., but as far ... 1answer 82 views ### How uncertainties affect values If I calculate the equivalent resistance of a circuit, for example:$$1/R_{eq} = 1/R_1 + 1/R_2 + 1/R_3 = 1/1472 + 1/3260 + 1/5580 \Rightarrow R_{eq} = 858.22\,\Omega$$And then calculate its ... 1answer 252 views ### Canonical momentum Velocity dependent Lagrangian I have a homework problem wich I think I'm on the verge of solving but need help with some relations: Show that if the potential U in the Lagrangian contains velocity-dependent terms, the ... 1answer 72 views ### Difference between periodic oscillation and periodic movement I'm dealing with a problem here. I'm not sure about the answer of this question: "What is the difference between periodic oscillation and periodic movement?". -For my opinion the difference is that ... 0answers 90 views ### Is the uniqueness theorem correct in superconductivity? There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions. We can treat superconductivity as a completely ... 1answer 343 views ### Inverse Square Law in Beta Radiation Setup: A radioactive source is placed at alternating distances from a Geiger Counter. Counts per second for 10 different distances (each spaced 1 cm apart) were taken for preset times ranging from 200 ... 1answer 136 views ### Why is there a sign error in my derivation? Adiabatic expansion of ideal gas: TV^{1-\gamma} is constant This is the last part of a derivation of the equation for an ideal gas undergoing reversible adiabatic expansion. I'm trying to prove that T V^{\gamma-1} is constant, but my result is that T ... 1answer 113 views ### Calculating sum of heat transfered I have a formula of thermal conductance heat transfer rate. Here it is:$$ Q = \lambda{S (T_1 - T_2) \over L} \Delta t $$For my calculations I have got some constant values available$$ Q = 0.58{1 ...
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A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
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### Reflection formula for spherical surface from Fermat's principle (Query)

The snip shows a part of the method shown by my teacher, to describe the reflection formula for spherical surface. However I do not understand how the relation of AB and BI (which I have ...