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.

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8 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 ...
-3
votes
0answers
36 views

Is the vector field conservative?

$$\mathbf{v}=(\frac{-y}{x^2+y^2},\frac{x}{x^2+y^2},0)$$ 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 $x$-$y$ ...
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2answers
13 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 ...
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0answers
26 views

Finding Hamiltonian to imitate this physics

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 = ...
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1answer
9 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 ...
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1answer
15 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 ...
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1answer
18 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 ...
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2answers
22 views

A simple pendulum having a solid metal bob

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 ...
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0answers
15 views

Final Temperature and Enthalpy Homework Question

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 ...
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1answer
9 views

2-D Elastic Collision

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 ...
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2answers
26 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 ...
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2answers
43 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
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1answer
23 views

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

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 ...
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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
1answer
21 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?

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 ...
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0answers
32 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: $$ L_{int}=g\frac{1}{4}\phi^4 + g'\phi^3\chi +... $$ How does the trivial diagram (i.e. just a cross with a vertex at the center) ...
-2
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1answer
28 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 ...
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1answer
45 views

How to get $a(t)$ and $v(t)$ from $a(x)$ without knowing $x(t)$?

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 ...
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1answer
20 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
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1answer
39 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 ...
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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 ...
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0answers
24 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 ...
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1answer
35 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 ...
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1answer
30 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
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0answers
29 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 ...
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2answers
28 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
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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.
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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
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0answers
29 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
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0answers
11 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
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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
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0answers
13 views

Stokes law percentage error

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
36 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
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4answers
38 views

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

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
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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
62 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
37 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
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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
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0answers
24 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 ...
-3
votes
0answers
47 views

Physics Centripetal Force problem [on hold]

At what rate a space station 200m in diameter would have to rotate to create gravity equal to 0.7 that at the surface of earth. How fast does it spin, and how long would it take to make a complete ...
0
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1answer
18 views

Estimating the characteristic energy of the neutron

I'm trying to do a question which is as follows: "Applying the uncertainty principle on the smallest scales, estimate the characteristic energy of the three relativistic quarks confined within ...
0
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1answer
26 views

Helmholtz energy in terms of grand partition function

According to my source of notes $$A = kT \left ( N \ln z-\ln Z(z, V, T)\right) $$ where $z=e^{\beta \mu}$, $\mu$ being chemical potential, $Z(z,V,T)$ is partition function for grand canonical ...
0
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0answers
21 views

Force required for balancing a three-bodied frictionless and gravityless system [on hold]

Hello everyone, I made calculations over calculations but I think my free body diagrams were wrong. There are three bodies here: on two of them (the 2 and 3) are applied two forces (F2 and F3) ...
0
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0answers
29 views

Question about a solution of a partial differential equation by separation of variables

I'm trying to understand this text: http://www.ekayasolutions.com/UCDMath/HeatCondSphere.pdf But I'm having problem with this part: Whe have to solve: \begin{equation} \dfrac{\partial ...
-2
votes
0answers
23 views

Find the period of a pendulum system [on hold]

How to solve the following problem, A mathematical pendulum is formed by a cable with length $l$ and a sphere at it's end with mass $m$. While the pendulum swings at it's position of ...
-4
votes
0answers
37 views

The question is related to quantum mechanics [on hold]

The energy gap in germanium is 0.72 eV. Find the maximum wavelength of electromagnetic radiation which can cause transition from the valance band to the conduction band.
-1
votes
1answer
24 views

Calculate the pressure in a container given moles and volume [on hold]

Say there are two containers with the same volume. The first has a temperature T and pressure P and contains 1 mole of $O_2$. The second has a temperature 2T and contains 1 mole of $He_2$. I'd like to ...