Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [homework-and-exercises]

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.

2
votes
1answer
33 views

Time after which the 3 particles will meet?

Problem is from Classical Mechanics: I am a beginner in Physics trying to understand the solution to the given below problem. Problem Statement: 3 particles are placed at the vertices of an ...
0
votes
0answers
22 views

Using Kinematic Equations when acceleration is not constant due to drag force

If you drop a ball in a vat of oil with a mass of 50 g and it reaches terminal velocity of 0.032 m/s, how long would it take to reach 1/2 of terminal velocity? The drag force equals $F_d$ = Dv. I ...
0
votes
2answers
24 views

Frictional force between ground and sphere

In this question I was asked to draw the free body diagram of the sphere. In the free body diagram, there were two forces in horizontal direction (1) normal reaction from wall (2) horizontal ...
0
votes
1answer
38 views

Prove that a transformation is canonical by using $\mathbb{M}^T\cdot \mathbb{J}\cdot \mathbb{M}$

So, I was given the following problem to solve: A system with two degrees of freedom is described by the following hamiltonian \begin{equation} H=p_1^2+p_2^2+\frac{1}{2}(q_1-q_2)^2+\frac{1}{8}(...
0
votes
0answers
20 views

What's wrong with my work? (calculate spring stiffness constant) [on hold]

So the prompt is as follows: A 1100 kg car moving on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.3 m. What ...
0
votes
3answers
22 views

The Lagrangian for gravitational potential energy in a double pendulum

For a double pendulum what would be the gravitational energy. I am trying to work out the Lagrangian for the double pendulum. I got the kinetic energy but I am struggling on the gravitational ...
0
votes
0answers
17 views

Damped forced vibration Calculating amplitude and phase angle

Consider that we have the following forced vibration with preload ($kxo$) spring. $$m\ddot{x}+c\dot{x}+k( x+xo) = F_0 \sin{(\omega t)}$$ Assuming that the solution must be a harmonic form but with ...
0
votes
2answers
48 views

Hamiltonian in Piers Coleman - Introduction to Many-Body Physics book

In the book "Piers Coleman - Introduction to Many-Body Physics (2016, Cambridge University Press)" in page 491 When an electron pair is created, electrons can only be added above the Fermi ...
-4
votes
1answer
26 views

What are typical atomic densities of solids and gases? [on hold]

What are average values for the number of atoms per cubic cm for typical solids and gasses at atmospheric pressure?
1
vote
0answers
27 views

Seeking affine reparameterization of a curve [on hold]

A ray of light propagates along the straight line $$x(p) = \frac{p}{\sqrt{3}}$$ $$y(p) = \frac{p}{\sqrt{3}}$$ $$z(p) = \frac{p}{\sqrt{3}},$$ where $p$ is a parameter. Reparameterize this curve with ...
0
votes
0answers
9 views

What angle does an unwinding ball makes

A particle like ball is connected to one end of a light inextensible cord, other end of which is connected to a very thin frictionless fixed vertical rod. The entire length of the chord is wound ...
0
votes
0answers
15 views

How to find moment of inertia about centriodal axis in easiest way?

Actual question is Find the moment of Inertia of the cross-sectional area of an I section about its centroidal axis: My solution: Here $A_{1}, A_{2}$ and $A_{3}$ are the areas: Centriod at X axis;...
0
votes
1answer
40 views

Calculating exact energy levels of perturbed Hamiltonian

I wish to find the exact energy levels of the following perturbed hamiltonian. $$\hat{H}=\frac{p^2}{2m}+\frac{m\omega^2}{2}x^2+\alpha x+\beta p^2.$$ I believe that it can be solved by using the ...
0
votes
0answers
29 views

Finding eigenvalues and functions for Hamiltonian (perturbation theory)

I am trying to find the Eigenvalues for the following equation (which comes from the Pauli equation when $p^2/m^2c^2\ll 1$): $$i\hbar\frac{d}{dt}\psi=\left[\frac{\vec{p}^2}{2m}-\frac{e}{2mc}\left(\vec{...
0
votes
0answers
17 views

D'Inverno Exercise: velocity between reference frames given angle of a rod

I'm trying an exercise from D'Inverno book "Introducing Einstein's Relativity" that says S and S' are in standard configuration with $v = \alpha c$ $(0 < \alpha < 1)$. If a rod at rest in S' ...
0
votes
1answer
48 views

Finite potential well; finding the energy “in a limit”

I've come a across the following variant of the finite-potential-well-problem in quantum mechanics: The potential is given by $V(x)=0$ for $|x| \geq a/2$ and $V(x)=-V_0/a$ for $-a/2<x<a/2$ where ...
0
votes
2answers
26 views

Acceleration due to central forces in the Lagrangian

On Wikiversity it states that for central forces: Wouldn't $\ddot{\vec{r}}_1$ be the same as $\vec{g}$?
-2
votes
2answers
50 views

Vector Significant Figures [on hold]

I was answering a question and I was told that I should observe proper significant figures. The question is: A car travels 9.00 Km East and then 6.00 Km, 30.0° North of East. Find the displacement of ...
1
vote
0answers
25 views

What importance of battery “ voltage” between cathode and anode in photocell? [duplicate]

In photocell at threshold frequency $f=f_0$ and voltage $>0$ (between cathode - and anode +) Is current $=0$ at $f=f_0$ and $v>0$? When voltage $>0$ and $f=f_0$, Does photoelectron have KE ...
-1
votes
1answer
21 views

The maximum height reached is [on hold]

In this question below  The maximum height which is being asked is the max height achieved from that elevated point A right? Because the formula which we have used just tells when the velocity of the ...
-1
votes
2answers
35 views

Are these resistors in parallel or series? [on hold]

So I am trying to find power dissipated in R2 but I have 2 different answers for if the resistors are in series or parallel and both answers are part of the options in the multiple choice to choose ...
-1
votes
1answer
29 views

What is the $x$-coordinate at $y=0$?

so I was doing this question and i initially got the answer but stumbled upon a question that came to my mind here from the time interval 8-12 seconds there is straight line graph due to uniform ...
-1
votes
0answers
11 views

How to solve wedge block problems considering velocity of block in ground reference frame [on hold]

How to solve this question considering velocity of block directly into ground reference frame I have already solved it considering. Velocity of block in wedge reference frame
1
vote
1answer
20 views

Swinging Atwood and Hoop And Pulley Lagrangian

The picture is showing the swinging atwood and a hoop and pulley. I know the lagrangian for both two, I have no problem with the kinetic energy of both but i couldn't convince myself that for the ...
-1
votes
0answers
11 views

A conducting sphere of radius R has two spherical cavities [on hold]

A conducting sphere of radius R (see photo) has two spherical cavities of radius a and b. The cavities have charges Qa and Qb respectively at their centres. Find (i) The electric field and electric ...
-1
votes
0answers
18 views

How to solve this Compound Circuit? [on hold]

How can I solve this circuit? If R4 is absent I know I can reduce R6, R5 and R2 to a series in parallel with R3. With R4 there how does the current flow when it reaches the junction of R3 and R4 AND ...
0
votes
0answers
32 views

A balloon starts rising upwards with constant [on hold]

So i was doing this illustration when I looked up the solution given below it I got confused at a certain point . Everywhere the acceleration $a$ of the balloon is taken into consideration so where ...
1
vote
1answer
16 views

Punch weapon vs. Swing weapon ,which applies more force to target?

Have been told the punch weapons i.e. katar impact with more force than a swing weapon i.e. broadsword . My question is simple which applies more force to target with an impacted hit ? Please back up ...
1
vote
0answers
57 views

How can we evaluate the following integral using the tricks of delta functions? [migrated]

I am trying to teach myself the statistical field theory formulation of statistical mechanics. Not part of a class, just self study in my free time. I appreciate any help here. I am starting with ...
1
vote
2answers
36 views

Force of repulsion between 2 hemisphere of different charge density [on hold]

Consider two hemispheres of radius r which are given a uniform surface charge density of $\sigma_1$ and $\sigma_2$. Find the force of repulsion when these two hemispheres are grouped together to ...
0
votes
0answers
28 views

Four-Divergence of a massive vector field in the interaction term

In an exercise is given the following Lagrangian $$\mathcal{L} = -\frac{1}{4}F^{\mu\nu}F_{\mu\nu} + \frac{1}{2}MA^\mu A_\mu + \bar\psi(i\gamma^\mu\partial_\mu - m)\psi + \mathcal{L}_{int}$$ with the ...
0
votes
0answers
33 views

River boat problem when speed of river is equal to speed of boat relative to river [on hold]

the river moves in a circular path and the drift is hence (root 3 omega ) but how to find the time taken by the boat?
-7
votes
0answers
34 views

finding result by transforming equations.any 3 questions [on hold]

The football ball m=1kg was kicked up vertically with speed v=20m/s. Make the graph of speed and the y position. The stone was thrown horizontally with speech v=10m/s, from the building at high h=15m. ...
-5
votes
0answers
27 views

physics,finding result by transforming equations [on hold]

The football ball m=1kg was kicked up vertically with speed v=30m/s. Make the model of movement track, also the graph of speed, knowing that Fr=bv2 , b=1 N/m2
3
votes
3answers
146 views

How does a particle move under a constant 4-force?

This question pertains specifically to the case of a constant pure 4-force in special relativity, of the form $\textbf{F} = (f_0, f_x, 0, 0)$, where $f_0 = \frac{γ}c \frac{dE}{dt}$. I understand how ...
0
votes
2answers
68 views

Basics of simple harmonic motion

I was told in my class that simple harmonic motion (SHM) describes the motion of the projection onto a straight line of the motion of a particle undergoing uniform circular motion (i.e. with constant ...
0
votes
1answer
40 views

What is tension in cabel of elevator? [on hold]

A block of mass $m$ is kept on the floor of an elevator of mass $M$ and the system is accelerating upward with acceleration $a$. The acceleration due to gravity is $g$. $F_n$ is Normal force on Block. ...
0
votes
0answers
23 views

Maximum velocity of an electron across a tube with potential [on hold]

Sorry i usually don't ask such fundamental or silly questions but I'm having trouble with this. I'm nearly sure I'm right doing this question based on an x-ray whereby an electron is hypothetically ...
0
votes
0answers
51 views

Special relativity application to a problem [on hold]

Disclosure: This is a homework problem You are on the earth when Einstein starts running away from earth at a speed of $\,0.1c$. When he is $3$ light years away from you (according to you), he ...
0
votes
0answers
33 views

Pressure in the pipe when the pool is draining out

I have a question: the situation is as follows: There is an open pool (in blue) to which a pipe is connected. The pressure above the pool is equal to the air pressure = 1 bar. In normal configuration ...
1
vote
1answer
42 views

An aircraft executes a horizontal loop at a speed of 720 km/h with its wings banked at 15°. What is the radius of the loop?

Though I solved the question as in the image: Solution: Taking Normal force on aircraft as N. $$\begin{array} {l}{N \cos \theta=m g, \quad N \sin \theta=\frac{m v^2}{R}} \end{array}$$ which gives ...
1
vote
1answer
34 views

Generalized Coordinates Property for a System of Particles

I"m looking at "Principles of Dynamics: Second Edition" by Donald T Greenwood. I'm trying to figure out how he obtains Eq. (6-64) $$\frac{\partial\dot x_j}{\partial\dot q_i} = \frac{\partial x_j}{\...
1
vote
1answer
38 views

Help in calculating Partition function and choosing the ensemble

I've been given this situation "A surface contains $N$ identical atoms in a fixed position. Every atom can occupy one of two states with energies $E_1$ or $E_2$ and the temperature is $T$." For ...
0
votes
0answers
24 views

Energy in an RL-circuit [on hold]

Given a circuit made of an electrical resistance $R$, a solenoid $L$ and a battery with voltage $U_0$, I have to calculate (i) the total energy up to $t=\frac{L}{R}$ (switch is closed at $t=0$) (ii)...
0
votes
0answers
18 views

Moment of inertia about of a square about an axis inclined at angle to one side [on hold]

Question-:Find moment of inertia of a square of mass M and side length 'a' along an axis lying in the same plane inclined at an angle 15° to one of its sides and passing through vertex. My attempt-:I ...
-1
votes
1answer
48 views

Dropping a stone velocity

I'm asked to calculate a stone being dropped from rest to hit the water it takes 2.7s I found the final velocity to be 26.46m/s
0
votes
1answer
40 views

How to find equation of state of an ideal gas from heat capacity?

I'm having a problem where I have to derive the equation of state of an ideal gas from the formula for molar heat capacity $C=C_V+ \beta V$. Is this even ideal gas? Can someone help me, or at least ...
0
votes
3answers
79 views

Infinite entropy in ideal gas

Does it make sense that entropy goes to infinity as temperature goes to infinity? For an ideal monoatomic 1D gas I have an expression for entropy \begin{equation} S=Nk_{B}Ln(\frac{Ve^{\frac{5}{2}}\...
0
votes
1answer
44 views

How much force is required to keep an asteroid travelling at 500 m/s in a staight line through deep space [on hold]

will it require no force because it is deep space or will something happen, like slowing down. The asteroid was already travelling at 500 m/s.
0
votes
2answers
66 views

Why is the weight multiplied by 2 and not one for this moment question?

Hi, I have my physics gcse tomorrow and in my CGP guide, to find the anti-clockwise moment they multiplied the weight by 2 and not one even tho it says 1m on the right of the pivot, is this due to the ...