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)

-1
votes
0answers
7 views

Something about equipotential lines for prospecting [on hold]

I'm an engineering student in geophysic and need that information.
1
vote
3answers
9 views

Doesn't rotational KE of a rolling marble change if there is no friction to provide torque?

The question arise from the following situation: A marble at the border of a uniform bowl begins rolling within it from rest. There is enough friction in the first half the bowl for the marble to not ...
-2
votes
0answers
16 views

showing that the qubit state α|001〉+γ|100〉 can be written as a product state of two of the qubits and the remaining qubit [on hold]

I need to show that the state α|001〉+γ|100〉 can be written as a product state of two of the qubits and the remaining qubit? I have tried this α|0〉∣01〉+γ|10〉∣0〉 α(|0〉+∣1〉)∣01〉+γ|10〉(∣0〉+∣1〉) ...
0
votes
2answers
31 views

Is there any difference between relative motion and motion itself

If relative motion is the change in position of a body with reference to another body, and motion is the change in position of a body with time . Then why is relative motion not associated with the ...
-3
votes
0answers
14 views

Tensile stress in stationary wave [on hold]

The equation of a stationary wave in metal rod is $y=0.002 \sin(\pi x/3) \sin(1000 \pi t)$, where $x$ and $y$ are in cm and t in seconds. Find the maximum tensile stress at point $x=2$ cm if Young's ...
-2
votes
1answer
21 views

Switching off Magnetic Field [on hold]

A line charge (charge per unit length 'k') is put onto rim of wheel of radius 'R' which is then suspended horizontally, so that its free to rotate (spokes are made of non conducting material). In ...
-2
votes
0answers
17 views

Electromagnetic Induction in a loop due to time varying current [on hold]

A rectangular loop (length L and width W) is placed in x-z plane such that one of its width is along x-axis while one of lengths is along z axis. At a distance 'y' from origin a long wire carrying ...
0
votes
0answers
10 views

What decide if the block will topple? The torque, or the angular speed

I'm confronting a problem that is common of toppling. A bullet hit a block and let the block start to rotate with constant angular speed around the corner of its bottom. We deal this problem by ...
-4
votes
0answers
45 views

Is the vector field conservative? [on hold]

$$\mathbf{v}=(\frac{-y}{x^2+y^2},\frac{x}{x^2+y^2},0)$$ is a vector field. If we need to find $$\int_{S}^{}(\nabla\times\mathbf{v}).d\mathbf{a}$$ over a hemispherical surface placed on the $x$-$y$ ...
0
votes
2answers
17 views

Momentum when a people fall down to ground (Related to momentum, gravity, lever)

According to the Newton's laws, free fall is subjected to the pull of gravity at acceleration of 9.8 m/s per second. (Something like this) But I don't think the principle of "free fall" is applicable ...
0
votes
0answers
29 views

Finding Hamiltonian to imitate this physics [on hold]

I have the following assignment problem I need help with A two state quantum system has basis states |+> and |->. These basis states are not eigenstates of the Hamiltonian of the system. At t = ...
0
votes
1answer
11 views

Rest mass of a moving particle that decys into two phtons

A particle of rest mass M is moving along the positive x direction. It decays into two photons having energies 1 GeV and 0.82 GeV, and these go in different directions making angles of 45 and 60 ...
0
votes
1answer
17 views

Solving for the initial height of a projectile

The problem is stated as follows; A cannon is placed at the edge of a cliff at an angle of $30^o$ (With respect to the x-axis) and fires a projectile with initial velocity of $20 m/s$. The ...
0
votes
1answer
41 views

What does it mean to say that something is “relativistic for an electron”?

I want to understand a concept better. I did a homework problem where I solved it all the way, then checked my answer with a solution set. My answer was different, so I followed the solution set from ...
-2
votes
2answers
23 views

A simple pendulum having a solid metal bob [on hold]

A simple pendulum with a solid metal bob has a time period T. The metal bob is now immersed in a liquid having density one-tenth of that of the metal bob. The liquid is non-viscous. Now the period of ...
-1
votes
0answers
22 views

Final Temperature and Enthalpy Homework Question [on hold]

3-36E A spring-loaded piston-cylinder device is initially filled with 0.13 lbm of an R-134a liquid-vapor mixture whose temperature is −30°F and whose quality is 80 percent. The spring constant in the ...
0
votes
1answer
9 views

2-D Elastic Collision [on hold]

A bocce ball moving at 3.60 m/s strikes a second identical ball initially at rest in a perfectly elastic collision. The first ball moves off at a 36 degree angle from its original path and ...
0
votes
2answers
30 views

The separation between the two plates of a capacitor is increased

I had the following question on a quiz recently: A capacitor consisting of two parallel plates, separated by a distance $d$, is connected to a battery of EMF ε. What happens if the separation is ...
1
vote
2answers
46 views

A problem about the harmonic oscillator in Quantum mechanics

When I learned quantum mechanics by reading Griffith's book called Introduction to quantum mechanics, I was confused by his description. In Page 53 of the 2ed edition book, after got the recursion ...
-3
votes
1answer
23 views

A car with mass 840 Kg is rolling at 50ms^-1 and is suddenly opposed by a friction force of 120N [on hold]

A car with mass 840 Kg is rolling at 50ms^-1 and is suddenly opposed by a friction force of 120N. a) Find the Acceleration. b) How long does it take the car to stop. c) How far does ...
0
votes
3answers
19 views

Pressure and altitude

I am going to ask a simple question, for sure. The pressure with respect to the altitude is given by this formula Where sea level standard atmospheric pressure p0 = 101325 Pa sea level standard ...
0
votes
2answers
25 views

The image of a wall clock is to be obtained on the opposite wall 2m away by the means of a convex lens. What is the minimum focal length required? [on hold]

I'm in 10th grade and this question came in my physics test. Nobody was able to answer this question correctly except my physics teacher who says that the answer is 2m. My answer is that there should ...
0
votes
1answer
48 views

How did he find the “lambda” value in this question? [on hold]

There is a pdf i found when searching about Lagrangian Multpliers, but i was not able to understand how he derived lambda from two differential equations. If anyone can walk me through it, i would be ...
0
votes
0answers
44 views

In a $\phi^4$ theory, does the single vertex Feynman diagram (with no internal propagators) contribute to the scattering amplitudes?

If I have an interaction term in the Lagrangian of the form: $$ L_{int}=g\frac{1}{4}\phi^4 + g'\phi^3\chi + \dots $$ How does the trivial diagram (i.e. just a cross with a vertex at the center) ...
-2
votes
1answer
29 views

Phase differences due to reflection etc [on hold]

http://www.physicsgalaxy.com/lectures/1/30/1749/Solved-Example-15#42 see this link(only question) and see 1:21. Phase difference is given as $2\mu t$ but shouldn't it be $2\mu ...
0
votes
1answer
49 views

How to get $a(t)$ and $v(t)$ from $a(x)$ without knowing $x(t)$? [on hold]

Suppose to know, for a one dimensional motion of a particle, the acceleration as a function of the position $a(x)$. Using $\frac{dv}{dx} v=a(x)$ I can get $v(x)$ as a function of the position. Is ...
0
votes
1answer
21 views

Mechanics of Rotational Motion [on hold]

Well, I faced a problem in my Physics Examination Problem: A Circular Disc of Mass $M$ and radius $R$ is set rolling on a table. If $\omega$is angular velocity, ST total energy ...
0
votes
1answer
41 views

What effect would GW150914 have had over a much shorter distance? [duplicate]

In the wake of the recent news of the confirmation of the existence on gravity waves, I was discussing gravitational waves with a friend, and he asked whether this could potentially lead to some kind ...
0
votes
1answer
31 views

Exercise 18b in Schutz's First course in GR

The question is as follows: Show that a timelike vector and a null vector cannot be orthogonal. So we have a timelike vector $\vec{A}$, s.t $\vec{A}^2<0$; and a null vector, $\vec{B}$ s.t ...
0
votes
0answers
25 views

Question on Law of Conservation of energy? [on hold]

A body of mass $m$ is thrown upwards with a velocity $u$. At a point $x$ metre above the ground, the ratio between kinetic energy and potential energy is 1:5. What will be the new ratio at $x$, if the ...
0
votes
3answers
65 views

$F\cos\theta$ is not proportional to $d\cos\theta$?

If I’m working in two dimensions and I wanted to calculate the net electrostatic force on charge C, where charges A and B are stationary, of the same charge, and placed on the y-axis equidistant ...
0
votes
1answer
31 views

Reference point for U tube question

Referring to the following diagram, I am expected to pick out the one case where the fluid in the tube is not in static equilibrium. They are in the other three cases. The answer is that situation 2 ...
-1
votes
0answers
31 views

Physics specific heat question [on hold]

The instructions below outline the procedure for a demonstration. Materials: four 100 g metal blocks, each of a different metal, four polystyrene foam cups, each containing 150 g of 10°C water ...
0
votes
2answers
29 views

Proving charge on outer surface of parallel plate capacitor must be zero

If we have two conducting plates, with charge $Q$ and $-Q$, why is the charge on the outer surfaces of each conductor zero? I've been trying to wrap my head around the problem. Firstly, don't excess ...
-1
votes
0answers
15 views

Capacitor charge [on hold]

It takes 14.8 J of energy to move a 13.0-mC charge from one plate of a 17.0-μF capacitor to the other. How much charge is on each plate? Assume constant voltage.
1
vote
0answers
24 views

Acceleration 4-vector in Schwarzschild metric [on hold]

I am working on A note of a paradoxical property of the Schwarzschild solution by Abramowicz M. A. and Lasota J-P It is a note on surprising cases in the context of the standard Schwarzschild ...
1
vote
0answers
30 views

Two Dimensional Momentum [on hold]

[2] []3> A tennis player receives a ball of mass $60\ \mathrm g$ travelling horizontally at $55\ \mathrm{ms}^{-1}$ perpendicular to the net, and returns it at $28\ \mathrm{ms}^{-1}$ in a direction at ...
0
votes
0answers
12 views

Find total elongation problem? [on hold]

The main question is like this The answer is total elongation = 4FL/AY But in the middle part wouldn't there be a compression . I think there will be a compression . Please clear my confusion
1
vote
1answer
19 views

Speed of pinewood derby car

If I drop a pinewood derby car from 4 feet I know it hits the ground in half a second at about 10.6 mph. If it rolls down the track (starting at 4 feet) it takes longer, but is it possible for it to ...
0
votes
0answers
13 views

Stokes law percentage error [on hold]

I am supposed to find the % error in t , r and D this is for Stokes law to find the viscosity.I have tried to find the % error in t we used a stopwatch so I found the mean from my values for t and ...
1
vote
0answers
38 views

Charge distribution on a line [on hold]

Given a conducting line segment from -a to a, with a total charge Q distributed by the continuous charge density $\lambda(x)$. I can write this system of integrals. Since the charge must total Q: ...
1
vote
4answers
39 views

How can I calculate how high an arrow goes when all I know is its initial speed? [on hold]

I'm not familiar with English physics terms so bear with me. If I shot an arrow straight up and it went off with a speed of 21 m/s, how high up would it go? (air resistance is insignificant). My ...
0
votes
2answers
43 views

How to find the current source Is and the voltage V1 of this circuit schematic? [on hold]

I have Vs= 1.5V, R1=1 Ohm, R2 =6 Ohms, I got the equivalent resistance to be 7 Ohms. Then I set equal Req to Vs for 7I=1.5 and got my current source to be 0.214A. Since it is only Vs and Req in the ...
0
votes
0answers
17 views

induction of voltage from power lines to telephone lines [on hold]

A pair of isolated parallel power lines of 1 cm radius with a separation of 90 cm have a voltage difference of 440 V. These power lines are 60 cm above a pair of telephone lines. The telephone lines ...
1
vote
1answer
63 views

Sakurai Exercise 2.17 (Harmonic Oscillator, Ladder operators) [on hold]

I the field of the harmonic oscillator and ladder operators I am trying to solve exercise 2.17 from Sakurai and want to proof the following relation $$ \langle x^{2n} \rangle = (2n - 1)!! \langle ...
-1
votes
0answers
11 views

Compton Scattering problem verification [on hold]

A photon emergre in an angle $\theta=\frac{\pi}{4}$ in a Compton scattering the kinetic energy of the photon is $K_i=2K_f$. I must find $K_i$ in $MeV$. $\lambda_f -\lambda_i= \lambda_c$. Then: ...
-1
votes
1answer
39 views

Confusion in a problem

This is a very basic homework type question. I guess there is some intermixing of concepts in my head. Help. There was a question I came across - A ball of mass 0.2 kg is thrown vertically upwards ...
0
votes
0answers
24 views

Number of impacts nitrogen molecules make with the palm of a hand [on hold]

What is the number of impacts one mole air makes with the palm of your hand assuming air is entirely made up of nitrogen?
-1
votes
0answers
25 views

Calculus Based Physics Problem with Particle Motion [on hold]

Suppose the position vector for a particle is given as a function of time by $$\hat{r}(t) = x(t)\hat{ i} + y(t)\hat{j}$$ while $$x(t)=at+b \text{ and }y(t)=c(t^2)+d,$$ where $a=1.00\, m/s$, $b=1.00\, ...
0
votes
1answer
22 views

If an object launches off of a table at a given velocity, calculate angle below the horizontal when it hits the ground?

So this is a basic kinematics question that I'm having trouble understanding. Here is the question verbatim: A hockey puck slides off the edge of a table with an initial velocity of 28.0 m/s and ...