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-like questions.

learn more… | top users | synonyms (3)

-2
votes
0answers
17 views

Why does depth and height replace volume in this problem?

In the following problem, why does H/𝛿 replace V/V? The two ratios have different units. Is there something I'm missing here?
0
votes
0answers
14 views

Thermal radiation

The emissivity of a hemi-sphere varies as: $$ e=E\cos\theta$$ What is the ratio of emissive energy between the given sphere and a normal black body sphere.
1
vote
0answers
25 views

Gravitational Strength on a theoretical flat planet

Ok, so let me clarify: a planet that overcame all structural problems with being planetary size, I.E. collapsing into a ball. What would be the gravitational strength on a flat planet with the ...
0
votes
2answers
30 views

Use of $g$ for centripetal acceleration

I have attached an image above including the question I'm unsure of (part B) In a nutshell, a satellite is orbiting Earth at the surface. Given is $g$ and the radius of the Earth. For part bi) the ...
-1
votes
0answers
28 views

What will be the new moment of inertia? [on hold]

Let assume we have a sphere of radius $R$, and we can simply calculate the moment of inertia if we consider the axis is going through the center O. Let's cut a sphere small radius $r$ from the sphere ...
-2
votes
0answers
25 views

Relative motion of a Boat [on hold]

An boat goes down a river in a velocity of 5 m/s relative to the river.At t=0 the man in the boat sees a bottle going down the river.If boat turn and start to return at t=30min, After how much time ...
1
vote
1answer
37 views

Relationship between position and momentum matrix elements

I am going through Faist's Quantum Cascade Lasers book. In the first section of the fourth chapter, he asserts that (in the context of a perturbative analysis of electronic transitions) the ...
-6
votes
0answers
24 views

the quantity of matter contained in a body is the ______ of the body [on hold]

I didn't understand this on my test I think it was mass
-4
votes
0answers
13 views

waves motion and sound and organ pipes [on hold]

in an open organ pipe whose one end is at x=0, the pressure is expressed by P=P0cos(3pi/2)sin(300(pi)t) where x is in meter and t in sec.then the organ pipe can be- a)closed at one end ,open at ...
-4
votes
0answers
90 views

A riddle with a physics related answer [on hold]

This question is from this book which has riddles with answers related to physics. I can't seem to get this one. My origins are humble. I started with a couple of people trying to understand ...
0
votes
0answers
39 views

High School Physics [on hold]

Two girls are standing on a bridge over a river. One girl falls freely and the other ties a rope to her legs. Both jump at the same time from the bridge. The length of the rope is more than the ...
0
votes
3answers
90 views

How much water did I actually drink? [on hold]

Water expands at temperatures over $5^\circ\mathrm C$ strictly monotonic. If you now drink $1~\mathrm{L}$ water ($5^\circ\mathrm C$) which will expand in your body on $37^\circ\mathrm C$, did you ...
0
votes
0answers
19 views

Fierz identity in Spin(5,5)

I am trying to understand(derive) equation 3.8 in 1208.5884 which is First, here $\gamma$ is $16\times 16$ chirally projected gamma matrices. which $\alpha=1,2,3,4,...16$ and $a=1,2,3,4,5,6,7,8,9,10$...
0
votes
2answers
52 views

Mass density of a cylinder increasing with the square of the radius

I’ve had to deal with a question like this on a test on friday and I just can’t get it out of my mind. I was supposed to calculate the moment of inertia of a cylinder with an inhomogenous yet ...
-1
votes
0answers
46 views

High School Physics-Electromagnetism [on hold]

An insulated smooth square frame ABCD of side $a$ is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
-1
votes
1answer
36 views

basic question about work exercise

I am learning independently from Tobochnik's statistical physics text. He asks a warm up question about work: A person pushes a block up a frictionless ramp. Is the work positive, negative, ...
-1
votes
1answer
31 views

Horizontal Velocity of a Projectile thrown from a Cliff [on hold]

If I were to throw a rock of a cliff at 12 m/s as a horizontal velocity, what will the final velocity of the rock become when it hits the ground? I am tempted to say 12 m/s because the horizontal ...
0
votes
3answers
87 views

How feasible is it to power your home with a bicycle? [on hold]

This article claims "60 Minutes On This Bicycle Can Power Your Home For 24 Hours!" How feasible is this claim? Sounds great - but the skeptic in me says "yeah, right." Hope this is an acceptable ...
1
vote
0answers
29 views

How does this dumbbell rotate?

I am reading the book Spacecraft Attitude Determination and Control by J.R. Wertz, and on page 488 it says: My question is: how does the axis of rotation, $\hat{\omega}$, rotate? How does ...
4
votes
1answer
45 views

X-Ray diffraction - Braggs law

"Based on the Bragg equation, if crystal A has larger spacing in its diffraction pattern than crystal B, what conclusion can you draw about the spacing between layers of atoms in A compared with B?" ...
1
vote
2answers
50 views

Question regarding elastic collisions and the conservation of momentum / energy [on hold]

I've been working on this question for a few hours and I cannot quite convince myself that my answer is correct. I've read the relevant section in my textbook, but I guess the lightbulb just isn't ...
-2
votes
0answers
43 views

How far would the atmosphere have to extend before we couldn't see the sun? [on hold]

Ignoring dust, haze, clouds or ice crystals. Just 100% clean air.
1
vote
0answers
24 views

Sectional curvature of 3-hyperbolic space [migrated]

For a pair of $(X,Y)$ of linearly independent vectors in $T_pM$, $p\in M$, the sectional curvature is defined as $$K_p(X,Y)= - \frac{\bigl\langle R(X,Y)X,Y\bigr\rangle}{|X|^2 |Y|^2 - \langle X,Y\...
-1
votes
0answers
22 views

Vertical Motion Question [on hold]

Question: An object is projected vertically to to the ground in a 20 m/s velocity. After 3 seconds another object is projected from the same position in the same velocity to the same direction. ...
0
votes
0answers
20 views

How to find the change in internal energy for a gas? [on hold]

So I'm given this problem, and for some reason when I solve for Q and delta U my answer is off, should be $\Delta U = 249.3J$ and $Q = 415.5J$ ...
2
votes
1answer
25 views

Principal moment of inertia for a rotating body

My major is not in physics. I am reading the following paper: (my problem is simple and not related with any optimization) http://arxiv.org/abs/1410.2841 (p.5~p.6) Suppose The ...
1
vote
1answer
39 views

Free particle Schrodinger equation: propagator

I am going through Shankar's Principles of Quantum Mechanics and am having trouble finding the free particle propagator $U(t)$ that satisfies $\lvert\psi (t)\rangle = U(t)\lvert\psi (0)\rangle$ due to ...
-2
votes
0answers
16 views

Simple harmonic motion [on hold]

A body executing shm has 10cm as amplitude and time period is 1.5s. Calculate the time taken by the body to travel a distance 5√3 cm from the mean position. I have used the formula x=asim(wt) And ...
3
votes
1answer
54 views

Velocity of satellite to crash into the earth

I was reading through this post today and was very impressed by the response that was given. However, what would have to happen to the velocity in order to collide with the Earth? Velocity of ...
-1
votes
0answers
13 views

Water Mist Problem? [on hold]

If a 150 USGPM 20 deg.C water in a 40 mm diameter with pressure of 25 bar need to be reduced to 2.5 bar through an orifice: will the water mist manifest?
2
votes
1answer
40 views

Simple Disk rolling with slipping on a horizontal plane

This is the first time I've encountered this scenario. I want to understand how to handle it. Since the disk is slipping, what would be the work done by the frictional force? What is the ...
0
votes
0answers
11 views

Determining velocity and angular velocity after a collision between two 2D rectangles [on hold]

Say I have two rectangles, which each have four vectors (which represent their vertices), a velocity, a mass, an angular velocity and a rotation (which is only used to simplify calculations as I don't ...
2
votes
0answers
28 views

Degeneracy of energy levels of a particle in a spherical step potential?

I have a particle of mass $m$ and spin $1/2$, in a spherical step potential, $$ V(r) = \begin{cases} 0 & r<a, \\ V_0 & r>a. \end{cases} $$ Now they ask me to find, without solving the ...
0
votes
0answers
48 views

Entanglement of bi- and tripartite pure and mixed states

since I'm not sure on how to find out whether a system is entangled or not I thought about examples that could clarify the whole thing. first example: system is in the state $\rho=1/2 (| 000 \rangle \...
1
vote
1answer
55 views

Trouble understanding Nielsen & Chuang exercise

I am probably just stuck on something very simple, but I'm having trouble understanding a premise of Exercise 10.40 in Nielsen & Chuang. The full details of the exercise are not important for my ...
0
votes
1answer
36 views

Bulbs glow with different brightness in one arrangement and the same brightness in the other arrangement

The question is: Mr.X decorated his house with fairy lights on a celebration.He bought 40 bulbs and operated at 220V. He found all the bulbs are glowing with different brightness. He called his friend ...
0
votes
0answers
24 views

Stuck with 2D kinetics problem [on hold]

I've been trying to solve this exercise for the last four hours and I'm totally stuck. The problems goes like this: Given the mechanism in the image, located in the vertical plane, the OB cord ...
-2
votes
0answers
24 views

Electric Field around Uniformly Charged Rod [on hold]

Question: A uniformly charged rod (length = $2.0~m$, charge per unit length = $3.0~nC/m$) lies on the x-axis. In consultation with your lecture notes, calculate the magnitude of the electric field at ...
-1
votes
0answers
35 views

Question about electric flux [on hold]

Question: Suppose a point charge is located at the center of a spherical surface. The electric field at the surface and the total flux through the sphere are determined. If the radius of the sphere ...
1
vote
0answers
35 views

From $\gamma$ to $\sigma$, finding proper basis

For $d$ dimensional case, usual gamma matrices have basis $\Gamma^A = \{1, \gamma^a, \cdots \gamma^{a_1 \cdots a_d}\}$ (Let's think about even case only for simplicity, I know for odd case only up to ...
6
votes
1answer
180 views

Potential function - numerical simulation

Using MATLAB, I fixed the potential in a region inside a rectangular plate (100 V) and in the border (50 V). I got the following result of the potential along the plate: I can't find an intuitive ...
-1
votes
0answers
15 views

Mistake in equating the induced EMF from a motional EMF problem [on hold]

I was going through problems like this: And solving for $\epsilon$ is straight forward: $$ \epsilon = -vBL$$ I tried the relationship: $$ \epsilon = -\frac{d\Phi_B}{dt} = - vBL$$ And never got ...
-2
votes
0answers
17 views

Finding the index of refraction [on hold]

I'm given the angle of incidence which is 60 degrees and the angle of refraction 27 degrees. And two possible indexes of refraction for the second medium which are 1.923 or 2.417. How do I figure out ...
-3
votes
0answers
38 views

Movement of a box containig a particle [on hold]

A small thought experiment: Imagine a rectangular box in space, containing particle, all resting at $t=0$ from your point of view. At some point in time $t>0$ the particle starts to move with ...
-1
votes
0answers
23 views

Projectile motion and bouncing [on hold]

Prove that the number of bounces n after throwing an elastic ball on a frictionless surface with a known angle (j)relative to the horizon and the angle of the initial velocity is known also (k)..is ...
0
votes
1answer
52 views

Conservation of Energy - Conceptual [on hold]

Two springs are attached by a piece of cloth. Both masses of the springs and of the cloth are negligible. The sizes of the cloth also are negligible. The initial tension in the springs are $|\vec{T}| =...
1
vote
0answers
43 views

standing waves on a string [on hold]

I've a problem that I can't solve, could someone please help me? The problem says: Two strings of a bass vibrate in a normal oscillation mode with the same period of 8.0 milliseconds. If the ...
-4
votes
1answer
28 views

projectile on an inclined plane [on hold]

Is the time of ascent equal to the time of descent? I tried it but I am not being able to prove it mathematically.
1
vote
1answer
39 views

I don't understand the approach used in solving this kinematics problem

The problem text is as follows: During the first half of a straight path, which is at $\alpha_1=60°$ relative to a reference line, a car is travelling at $v_1=72 km/h$. During the second half of the ...
-2
votes
0answers
32 views

Flat Disk Rotating Torque [on hold]

I have been trying to work out something. If you had a top like in the following description, how would you calculate the vector torque of the disk? And would it be just due to gravity? If so is the $\...