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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1answer
10 views

Car A (1500kg, travelling at 10 m/s) and Car B (1000kg, stationary) bump into each other. What is the momentum of Car A after the collision?

I calculated the total momentum to be 15000 kg m/s (I did 1500*10), but I how do I split up the momentum between Car A and Car B? I am probably missing something outrageously simple, but for some ...
1
vote
2answers
30 views

Number of revolutions of a rolling coin [on hold]

Take two quarters and lay them on a table. Press down on one quarter so it cannot move. Then, starting at the 12:00 position, roll the other quarter along the edge of the stationary quarter. How many ...
-3
votes
0answers
15 views

projectile motion angles [on hold]

A boy wishes to throw a ball through a house via two small openings, one in the front and the other in the back window being directly behind the first. If the boy stands at a distance of 5m in front ...
1
vote
2answers
1k views

Finding max height of a mass launched by a spring?

I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run. A block of mass $M$ is launched ...
0
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1answer
87 views

Geodesic deviation on a unit sphere

Very little interest in the original version of this question so I've rejigged it hoping for a more positive response. I'm trying to use the geodesic deviation ...
0
votes
1answer
39 views

Finding the divergence of this force [on hold]

I've got to find the divergence of this force, $$ \mathbf F=\left(x^2+y^2+z^2\right)^n\left(x\hat e_x+y\hat e_y+z\hat e_z\right) $$ I would know how to do it if the $n$ superscript wasn't there. Any ...
0
votes
1answer
34 views

Simple harmonic oscillator, calculate the trajectory in real space

Potential of a simple harmonic oscillator: $$U=\frac{1}{2}k x^2$$ I'm asked to calculate the trajectory of a particle moving in this potential, with initial conditions $x(t=0) = 0$ and $v(t=0)=v_0$. ...
2
votes
1answer
1k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
0
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1answer
27 views

Help understanding this differential equation of a varying electromagnetic field [on hold]

I'm reading some lecture notes (we're studying blackbody radiation and are approaching Planck's formula) but I'm struggling to understand exactly what's being said. So the lecture notes read as ...
0
votes
1answer
25 views

Error in measuring distance ignoring curvature of Earth [on hold]

Suppose you model distance as a flat 2d plane rather than a curved surface. Given that the radius of the Earth is about 6400 km, approximately how far must you travel before the relative error ...
2
votes
2answers
170 views

Projectile motion maximum distance to origin

Is there an elegant or easy way to derive the maximum distance from the origin to a point of the parabola created by projectile motion (assume initial position is the origin)? Other than ...
-1
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0answers
18 views

Find the smallest turning radius of a car, given velocity [on hold]

So, here's another homework question... A sports car is advertised to be able to "reach 60 mph in 5 seconds flat, corner at 0.85g, and stop from 70 mph in only 168 feet." At 60 mph, what is ...
0
votes
1answer
11 views

Various springs acting on a point mass

The force exerted on one spring is $\vec{F}=-k\vec{r}$. Now suppose we have N slinkys with stiffness $k_1,k_2,k_3,...,k_N$ where they have one end tied to fixed points in space with coordinates ...
-1
votes
0answers
21 views

Quadrature method (vertically falling particle) [on hold]

Consider a particle, that in the presence of the force of gravity, moves only vertically. Obtain the equation of motion of the particle from its mechanical energy(quadrature method). Consider the ...
1
vote
2answers
233 views

Calculating the change in entropy in a melting process

I have a homework question that I'm completely stumped on and need help solving it. I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
6
votes
1answer
219 views

Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
0
votes
0answers
39 views

Lorentz factor, derivation from 4-velocity vector [on hold]

How do I derive the Lorentz factor $\gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$, from the fact, that the velocity 4-vector $(-c,v_1,v_2,v_3)$ has length (norm) equal to 1?
1
vote
1answer
86 views

Closed expression for the Green's function for 2D Helmholtz equation over rectangular domain

I have to use the Green's function for the 2D Helmholz equation $$(-\nabla^2 - E) \psi(x, y) = 0$$ on the rectangular domain $[0, L_x] \times [0, L_y]$ with Dirichlet boundary conditions: $$\psi(0, y) ...
0
votes
2answers
1k views

Can you help me solve a difficult kinematics problem? [on hold]

I've been working on this problem for a while now, but I still don't know how to solve it. It involves 2D kinematics, which aren't in themselves hard, but this one threw me for a loop. A ball is ...
1
vote
2answers
56 views

Change of kinetic energy in a two particle collision

A problem I am working on proceeds as follows: A billiard ball of mass $M$ is initially at rest on a horizontal frictionless table. Another ball of mass $m < M$ and velocity $\mathbf{v}$ in ...
1
vote
0answers
22 views

Energy in a string [on hold]

A nylon string of length L = 50 cm and under a tension of T = 70 N is plucked with an amplitude of 5 mm. What is the energy in the string? Please give me the relationship between energy of the ...
0
votes
2answers
21 views

Thermodynamic equilibrium- mixing of gases

What is the final temperature and pressure after removing diaphragm of a cylinder which divides the cylinder into two equal components each of volume $0.1\,m^3$ and each component contains air at ...
1
vote
1answer
36 views

Joules To Move A Kilogram In Space [on hold]

If roughly ten joules lifts one kg on earth one meter, how many in space? Meter / joule/kilogram Kilogram/meter/joule
2
votes
0answers
23 views

What will be the time taken by a stone to reach the ground if it is thrown with velocity $v$? [on hold]

I was studying from my reference book and I got this question. I tried solving it by finding the total distance n average velocity but it didn't work please help me out.
1
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0answers
22 views

Finding equation for acceleration using mass1, mass2, gravity, theta, and Mu [on hold]

So, the only question I could not solve in this chapter for AP Physics, and I really want to understand it. We have a situation like this: There is a box sitting on an incline. We are trying to ...
1
vote
1answer
81 views

Which textbooks contain info on Bessel functions & their use as basis functions?

As an exercise my research mentor assigned me to solve the following set of equations for the constants $a$, $b$, and $c$ at the bottom. The function $f(r)$ should be a basis function for a ...
8
votes
1answer
175 views

The problem in Sredniki's textbook: How do I calculate loop corrections for $\phi\phi\to\phi\phi$ with this Lagrangian?

The problem in Sredniki's textbook 10.5 : For a free scalar field $\psi$, the Lagrangian is $$\cal{L}= -\frac{1}{2}\partial^\mu\psi\partial_\mu\psi-\frac{1}{2}m^2\psi^2$$ Here we use the metric ...
2
votes
2answers
5k views

What does y with a line over it represent?

I've been asked to complete this chart and have never come across this symbol before, nor can I find anything about it on google: What does the y with the line over it represent? And also, does the ...
0
votes
0answers
32 views

Sturm Liouville Problems [migrated]

I'm currently having a class at university that discusses Sturm Liouville Problems. We have to solve a few problems one of which I can't seem to solve. We use Advanced Engineering Mathematics by Erwin ...
2
votes
1answer
63 views

Doppler shift for a uniformly accelerating observer

This was given in textbook as an example. An observer on a spaceship with a four velocity $u$ is approaching from $x = +\infty$ a star at rest in the reference frame $S$ while undergoing constant ...
2
votes
2answers
30 views

Is a given charge density a surface charge density or volume charge density?

The exact question goes like this: In a certain electronic tube, electrons are emitted from a hot plane metal surface, and collected by a plane metal plane parallel to the emitter, at a distance ...
1
vote
1answer
37 views

Uncertainty in position and kinetic energy

How do you find the uncertainties for $x$ and $K$? Knowing that the general uncertainties = $$ \sigma_A \sigma_B \geq 1/2\int \psi ^*[\hat A,\hat B] \psi dx\, $$ I figured out the commutator, for ...
-4
votes
1answer
42 views

What causes a spacecraft entering the atmosphere to catch fire? [on hold]

What causes a spacecraft entering the atmosphere to catch fire? A) surface tension of air B) viscosity of air C) high temperature of upper atmosphere D) greater proportion of ...
0
votes
0answers
36 views

Kinematics/ Projectile Motion Lab [on hold]

This is a question from a projectile motion experiment. Using kinematics you will be asked to calculate the initial velocity of the projectile by measuring its vertical drop h, and the horizontal ...
1
vote
1answer
40 views

Normal modes of two parallel $LC$ oscillators coupled via mutual inductance

Consider the circuit shown below. The two LC circuits are arranged in such a way that their mutual inductance M results in a coupling between the currents flowing in the two circuits. Find the ...
3
votes
3answers
583 views

Prove a dielectric with infinite dielectric constant behaves as a conductor for static fields

I read the following problem: Prove that a dielectric medium for which $\varepsilon \to \infty$ behaves as a perfect conductor in the presence of static electric fields. So, the easy part is that the ...
-2
votes
0answers
20 views

To find angular speed of a rotating body [duplicate]

A body moving with uniform angular acceleration covers 100 pi (rad)in first 5 s. Its angular speed at the end of 5 s (in rad/s) is?? My ans is 40 pi, but according to the answer given in my book ...
-1
votes
0answers
16 views

To find angular speed of a rotating object [on hold]

A body moving with uniform angular acceleration covers 100 pi (rad)in first 5 s.its ang speed at the end of 5 s (in rad/s)is??
0
votes
0answers
25 views

speed of muons relative to Earth [on hold]

A certain muon detector counts 600 muouns / h at an altitude of 1900m and 380 / h at sea level. Given that the muon half-life at rest is 1.5 × ( 10^-6)s, determine the speed of the muons relative to ...
0
votes
1answer
48 views

When two objects roll down an incline, does the velocity increase?

I know the basics of rotational motion but this question just confused everything: The answer to the question is A. But why? My problems: If first, I treated both the disks as two particles, ...
0
votes
1answer
24 views

Image charge method to find electric field [on hold]

The following is a question from my tutorial on boundary value problems and image charge method- A point charge +q is placed at (0, 0, d) above a grounded infinite conducting plane defined by z = 0. ...
0
votes
0answers
35 views

Vectors in three dimensions [on hold]

A plane travels 40 degrees east of north from the Heliport travelling horizontally distance of 2km while reaching an altitude of 2500m and turns travels horizontally another 3km and loosing 1500m in ...
2
votes
1answer
76 views

Looking for a simple proof of symmetry of linear susceptibility tensor

Getting a diagonal susceptibility tensor: Define the linear susceptibility tensor as $\chi_{ij}$: $P_i = \epsilon_0\chi_{ij}E_j$, using standard notation for the electric field and the polarization. ...
0
votes
0answers
24 views

Kinematics - Projectile motion down an inclined plane

The inclined plane has angle A over the horizontal. A projectile is thrown down the inclined plane at angle B relative to the incline at velocity V. What is the time taken, range, and max ...
2
votes
1answer
336 views

Spring system - 3 DoF system and its properties while changing stiffness

I was given the attached 3 degree of freedom spring system with the purpose of analyzing it. I came up with the following equation of motion and then I ran Matlab to calculate the corresponding ...
2
votes
0answers
34 views

Conceptual question on helmholtz equation

Given the homogeneous Helmholtz Equation $[\triangledown ^2 + \kappa^2] E= 0$, I understand $\kappa$ represents the wavenumber $\omega_0 / c$. In light of this, what physical meaning can be taken from ...
0
votes
0answers
19 views

Propagation of Error Formula

I did a lab, and found the Hall voltage for different currents. From these, I was also given the direction, and magnitude of the magnetic field. I need to find the number of charge carriers per ...
0
votes
1answer
32 views

Temperature Gradient with varying $T$ [on hold]

I'm working on a problem which asks for the temperature gradient at the ends of the rod. The blocks (right and left) are both kept at 0 degrees C. The temperature of the rod is given by $T = ...
1
vote
0answers
24 views

Moment of Inertia of Polygons in the Plane [on hold]

I was reading this link, which describes a method of finding the moment of inertia of a general convex polygon by splitting it into triangles. I then realized I have no idea on how to derive a such a ...
1
vote
0answers
36 views

Potential due to a Uniform Ring [on hold]

Consider a uniform ring of mass $M$ and radius $a$ (?). I would like to prove that for $r > a$: $$\Phi(r) = \frac{GM}{r} \sum_0^\infty[P_n(0)]^2 \left(\frac{a}{r}\right)^n $$ Where $\Phi(r)$ is ...