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.

learn more… | top users | synonyms (1)

1
vote
1answer
43 views

How to find the electric field of a charged tube?

Let's say there is a charged tube(cylinder with no top or bottom) with radius $a$, length $l$ and charge $q$ and a point which is collinear with the centre of the charged tube. Anyway, since we can ...
1
vote
2answers
70 views

Energy to reach the moon

I've been stuck on this question for a couple of days now. Given that the potential energy of a 930 kg object on the Earth's surface is -58.7GJ, calculate the minimum energy required for the 930 ...
-1
votes
2answers
21 views

Finding power in series circuit

A resistor of resistance 12 ohms is connected in series with a cell of negligible internal resistance. The power dissipated in the resistor is P. The resistor is replaced with a resistor of resistance ...
0
votes
3answers
65 views

How fast would the Earth need to spin for us to feel weightless?

It's a classic question with many answers all over the Internet, but none here so I figured I'd ask it: How fast would the Earth need to spin for a person (or anything for that matter) to feel ...
0
votes
1answer
36 views

Expectation value of number operator $\hat{n}$

I'm studying for my quantum mechanics test and I've stumbled on this problem. They want the expectation value of $\hat{n}$, $\langle \hat{n} \rangle$, with this given $\psi$ at $t=0$: $$ \lvert ...
0
votes
1answer
16 views

How do I find the moment of inertia of a regular $n$-gon? [on hold]

Of a regular $n$-gon with radius $R$ and mass $M$. Any hint to solving would also be acceptable. The result I'm looking for is $$I_{CM} = (1/2) MR^2 (1 - (2/3) \sin^2(\pi/n)).$$
0
votes
0answers
31 views

Easy problem on mechanics(hooke's law) [on hold]

I thought a lot about this problem (However it's must be very easy ) At first, i would write the statement of problem and then my wrong solution. statement: Find the minimum stiffness of rope,so ...
-4
votes
0answers
27 views

Can human body survive a negative acceleration of $ 250m/s^2$ [on hold]

Can the human body can survive a negative acceleration trauma accident because of a sudden stop if the magnitude of the acceleration is less than $250m/s^2$. If you are involved in an automobile ...
-3
votes
0answers
29 views

Please tell me the way to solve the following question [on hold]

Question - Consider a box that is divided into two indentical parts of equal volume. The right half contains a gas of $N$ (=100, 500, 1000) particles and the left half is empty. A small hole is ...
1
vote
0answers
31 views

Find the field of two infinite strips of width $b$ [on hold]

Q:The two charged strips in the following picture have width $b$, infinite height,and negligible thickness(in the direction perpendicular to the page).Their densities per unit area are $\sigma$ ...
0
votes
1answer
25 views

What are overtones and how do they relate to harmonics?

Problem 43. Two organ pipes, a pipe of fundamental frequency 440 Hz, closed at one end, and a pipe of fundamental frequency 660 Hz, open at both ends, produce overtones. Which choice below ...
0
votes
0answers
7 views

How to figure out new vector direction after deflection by polar and azimuthal angles [migrated]

I have a direction cosine vector in Cartesian 3D space. The vector starting point is (x0,y0,z0) and direction {i0,j0,k0}. I need to find the new direction cosine vector direction in the Cartesian 3D ...
1
vote
2answers
71 views

How can I derive the Hamiltonian of simple harmonic oscillator from this Lagrangian?

I'm working through Leonard Susskind's Theoretical Minimum: Classical Mechanics and I can't seem to understand how the Hamiltonian of a simple harmonic oscillator is derived from the following ...
1
vote
1answer
21 views

$c/a$ ratio for an ideal hexagonal close-packed (HCP) structure [on hold]

Show that the $c/a$ ratio for an ideal hexagonal close-packed (HCP) structure is $\left(\frac{8}{3}\right)^\frac{1}{2} = 1.633$. I believe $a$ is the length of $a_1$ and $a_2$. I figured that ...
1
vote
2answers
35 views

DC Generator with magnet as rotor

DC generators convert the AC current in them by split ring commutators right and the graph of the current will be like this but the question is how would be the graph if the magnet is the rotor and ...
0
votes
0answers
14 views

What will be the electric field intensity? [on hold]

Ì have a problem here I tried to solve it but I am not able, so it goes like this. If the surface area is 10 cm2 and the electric flux is 25 NM2 C-1, find the electric field intensity?
0
votes
0answers
10 views

Boundary Work with saturated liquid, When to use Specific Heats?

I have a Thermodynamics question for homework that asks: ...
2
votes
1answer
82 views

Can these two terms cancel out?

In trying to prove that $$\Gamma_{\mu\nu\lambda} = \eta_{ab}J^a_bJ^b_{\nu\lambda}.$$ The author canceled out while expanding the first equation $$J^a_{\mu\lambda}J^b_\nu$$ with ...
1
vote
2answers
32 views

Solving equation of motion with exponential friction term

My friend's kid asked me this question. I have no idea how to solve it since I have stopped calculating mechanics for about 15 years since I graduated from high school. The question is: A boat that ...
1
vote
1answer
181 views

Advanced kinematics problem regarding $F = ma$ [on hold]

I really need help with this problem. Thank you for your time. Question: Look at the figure below. Derive the formula for the magnitude of the force F⃗ exerted on the large block (mC) in the ...
1
vote
1answer
29 views

A ball is dropped from the roof of a building. How fast is it moving after 4.9 seconds? (Absolute value) [on hold]

i really need help. A ball is dropped from the roof of a building. How fast is it moving after 4.9 seconds? (Absolute value) in m/s A water balloon is thrown downward from a tall building with an ...
0
votes
1answer
14 views

Flux through planes of a wind turbine [on hold]

The question asks how much wind will flow through each plane of a cube surrounding the turbine. the velocity of the wind is given by a function that depends on position according to v=(az,bz^2,c). The ...
0
votes
1answer
27 views

Potential Differences (Voltage) from Point Charges [on hold]

Identical +1.8 micro Colomb charges are fixed to adjacent corners of a square. What charge (magnitude and algebraic sign) should be fixed to one of the empty corners, so that the total electric ...
0
votes
0answers
8 views

Convex and Concave Bridges forces [on hold]

What are the forces acting on a car when travelling in a concave and convex bridge?
1
vote
1answer
67 views

Time evolution of a quantum system

A quantum system has Hamiltonian $H$ with normalised eigenstates $\psi_n$ and corresponding energies $E_n$ ($n = 1,2,3...$). A linear operator $Q$ is defined by its action on these states: $$ ...
1
vote
3answers
677 views

How can I find the potential created by spherical capacitor with dielectric material?

If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. What kind of a ...
0
votes
0answers
11 views

A homework about Electric field [on hold]

Set up a uniform electric field between two horizontal plates by charging the lower plate positively and the upper plate negatively. The plates have length L and separated distance d. An electron is ...
0
votes
0answers
18 views

average speed and velocity problems [on hold]

I have a science quiz tomorrow, and am lost about how to complete these problems. I know that speed=distance/time and velocity=displacement/time. keep in mind that in a freshman in hs.
1
vote
1answer
161 views

Heisenberg XXX time evolution operator for three qubits

I've a problem to reproduce the result in equation (4) on page three of this paper: http://arxiv.org/abs/0802.2588. So far I've understood that they apply a Heisenberg XXX interaction between ...
0
votes
0answers
15 views

Conductor related stuff [on hold]

I am having trouble dealing with conductors, especially the part where fields outside and inside are asked. The problem 7 deals with conductors. A detailed answer would help me.(Problem 6 not related ...
0
votes
1answer
26 views

Two-block system acceleration when applying a force in the $x$ direction

Two blocks are connected by a light-weight string that passes over a friction-less pulley (a.k.a. Atwood's machine). Block # 1 (called $m_1$) hangs from the edge of a friction-less table. Block # 2 ...
3
votes
2answers
232 views

So what is happening in this angular kinematics equation?

-The wheel of a car has a radius of 20 cm. It initially rotates at 120 rpm. In the next minute it makes 90 revolutions. What is the angular acceleration?_ So the answer is solved by using one of ...
1
vote
2answers
38 views

Draw the charge configuration according to the electric field [on hold]

I'm trying to draw the charge configuration outside the regions that lead to the given electric field patterns. Can someone show me how?
0
votes
0answers
13 views

Circuit Connections definitions in my homework [on hold]

How can i Define the Series & parallel Connections of Circuit? Define: Parallel connection : Series Connection :
1
vote
1answer
27 views

How does velocity relate to energy difference in Compton scattering?

I'm having trouble understanding what my professor is getting at asking in this question. I just visited her office and her explanation minutely helped. I'm hoping to get a bit more clarity on what is ...
1
vote
1answer
166 views

Question about superconductivity

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 $r_0<r<R$ ...
3
votes
1answer
44 views

Calculating time to reach certain velocity with drag force

I was given a problem for homework where we needed to calculate the time for a falling object to reach a certain velocity when accounting for drag force. I did it by setting up acceleration as a ...
1
vote
2answers
55 views

What do they mean by a pendulum losing seconds?

In many pendulum related question, a pendulum is taken do a different place where it loses seconds. For example: A second's pendulum is taken to a mountain and it loses 20 seconds per day. What ...
0
votes
0answers
20 views

Kinematic related question [on hold]

Question: A baseball is hit with a velocity of of 30 m/s at an angle of 42.6 degrees to the horizontal. An outfielder who is good at 2D kinematics knows he is exactly 8 meters from where the ball will ...
0
votes
0answers
25 views

Maxwell equations in cylindrical coordinates [on hold]

Give a coil of radius $R$ and $N$ turns crossed by a mean current of $I_0$ ampere at $10 MHz$ frequency (sinusoidal), I need to calculate the behaviour of the electrical and magnetic field inside the ...
1
vote
1answer
26 views

Finding the velocity of a ball thrown upwards [on hold]

A ball is thrown upwards with a speed of 16.1 m/s. What is the ball's velocity 1.6 seconds after it is released? I tried to solve this using the equation: $v = u+at$, substituting u for 16.1, a for ...
1
vote
0answers
14 views

Kinetic Damping Behavior [on hold]

For a problem I am given a block attached to a spring attached to a wall with mass m and coefficient of friction u. The magnitude when it is sliding is friction=$mgu$ opposite motion. It won't move ...
1
vote
0answers
24 views

Drag - Dimensional Analysis / Buckingham Pi

Dimensional Analysis / Buckingham Pi Theorem I'm working on dimensional analysis and I'm having trouble. Here's a problem from my book I'm working on for practice. I'm suppose to consider a small ...
0
votes
0answers
29 views

Where is the maximum center of mass so it doesn't fall over? [on hold]

I have some sort of barrow with brakes, which its deceleration due to the braking never makes the crate slide down: I have found it is $\mathbf{a} \leq g(\mu\cos\theta - \sin\theta)$ (note that it ...
1
vote
3answers
257 views

Two dimensional elastic collisions with varying angle of incident

If in an elastic collision I know all initial values and that mass for each object remains constant throughout the collision (but different from one another) how can I determine their final velocity ...
1
vote
1answer
40 views

How to calculate the photoelectric effect with photon efficiency?

I am not sure exactly where to go with this problem. The problem states: "A $1.3 \, \mathrm{mW}$ laser ($\lambda = 545 \, \mathrm{nm}$) shines on a cesium photocathode ($\phi = 1.95 \, \mathrm{eV}$). ...
1
vote
0answers
34 views

How torque and friction cause wheel to roll

I apologize if this question has been answered before, but I did not find the explanation that I needed. If a torque is applied to a wheel situated on a frictional surface, what forces cause the ...
1
vote
1answer
38 views

Loading a capacitor in an RC circuit

I have an RC circuit to which I am going to apply voltages of 5V every 100ns. So every 100ns, the capacitor will change its "state" from charging up to uncharging. I have been trying to find the a ...
0
votes
1answer
22 views

Finding the distance between two osclilating particles in a wave

Assume a wave function $\psi = \psi(x,t)$ where $x$ is position from the starting point $(0,0)$ and $t$ is time. Two oscillating points A and B are located at $x_1$ and $x_2$ respectively with $x_2 ...
1
vote
0answers
33 views

Laplace's equation with spherical, cylindrical, and planar symmetry [on hold]

Find the general solution to Laplace's equation for spherical symmetry (everything can only depend on $r$, the radius), cylindrical symmetry (everything can only depend on $s$, the radius), and ...