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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-2
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1answer
21 views

An interesting problem on vectors [on hold]

A particle subjected to two equal forces along two different directions. If one of the forces is halved, the angle which the resultant makes with the other is also halved. The angle between the forces ...
0
votes
1answer
10 views

Area covered by particle between it's path and horizontal lines

Question: The maximum range of projectile is R and the maximum height attained by the particle is H. If the area covered by the particle between its path and horizontal line is A, then A = ...
0
votes
1answer
52 views

Calculate orbit height from tangential velocity

Is it possible to calculate the altitude of a satellite orbiting a planet, just from the planet's mass and the satellite's velocity, assuming that the satellite is in a perfect circular orbit? If so, ...
1
vote
0answers
35 views

calculate force between two magnets [on hold]

I have used a couple of online calculators to estimate the attractive force between two cylindrical bar magnets. Using d=1"; t=1"; x=0.1"; Neo35 (Br=12,300 Gauss): source 1 gives 63.5 lbf source 2 ...
0
votes
1answer
53 views

Classical mechanics; gravitation question [on hold]

There is a crater of depth $R/100$ on the surface of the moon (radius $R$). A projectile is fired vertically upward from the crater with a velocity, which is equal to the escape velocity from the ...
-1
votes
1answer
1k views

Mixing Water at Different Temperature

If I have cup of water at room temperature (say, $25^\circ$C). What would be the resultant temperature if I pour another cup of same amount of water at $100^\circ$C to it? Is it simply ...
5
votes
2answers
103 views

Difference between weight of water and pressure of water

(I didn't even have a basic formal education in physics. I'm learning through the internet out of my own interest, so if there are any silly mistakes, kindly bear with and guide me through.) ...
0
votes
2answers
139 views

Why does the coefficient of performance need to be calculated with $W + Q$?

How much work must a heat pump with a COP of 2.50 do in order to extract 1.00 MJ of thermal energy from the outdoors (the cold reservoir)? The first formula that came into my mind after reading ...
1
vote
2answers
217 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 ...
4
votes
2answers
130 views

Gravitational slingshot maximum

I have recently read an article about gravitation slingshot assist used by Voyagers 1-2, and was thinking on why this hasn't been used for travel between solar and other systems. I mean sligshot can ...
0
votes
1answer
176 views

What strategy should I use to approach this problem? If my straight line approximation doesn't work [on hold]

recently i wrote an assignment in one of the questions i got two different answers for the same question by considering a straight line motion The question was somewhat like this THIS IS A HOMEWORK ...
0
votes
0answers
39 views

Lagrangian for FRW metric

For the metric $$ds^2=-dt^2+a^2(t)(dx^2+dy^2+dz^2),$$ $$L= \sqrt{-g_{\alpha\beta}\frac{dx^\alpha}{dt}\frac{dx^\beta}{dt}}$$ How does this become $$L= \sqrt{1-a^2 (\frac{dx}{dt})^2}~? $$ I guess ...
6
votes
1answer
207 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 ...
1
vote
1answer
188 views

Classical Rutherford scattering (partial) derivation

I am having trouble answering the following question, please could you help! Thank you in advance for any assistance you can give. Consider classical Rutherford scattering of a particle with mass $m$ ...
1
vote
2answers
125 views

A change of units in Bethe formula

I'm reading through the following paper: Monte Carlo simulation of non relativistic electron scattering by W. Williamson and G. C. Duncan. In the following paragraph, I want to know how to arrive at ...
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 ...
-3
votes
0answers
27 views

How to calculate integral? [migrated]

$\int_0^\infty\mathrm{d}l/(r^2+l^2)^{3/2}$ the solution is supposed to look like this, unfortunately I can't derrive it.
0
votes
2answers
23 views

Finding Interatomic Spacing

Here is the problem I am working on For what temperatures are the atoms in an ideal gas at pressure P quantum mechanical ? Hint: use the ideal gas law P V = N kT to deduce the interatomic spacing ...
1
vote
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
votes
2answers
25 views

Work done by a frictional force on a cylinder

A cylinder of mass $m$ and radius $R$, is rolled on surface with coefficient of kinetic friction $\mu_{k}$ about the axis passing through the center and parallel to the surface, with initial ...
1
vote
1answer
618 views

Magnetic field in a cylinder with an off-axis hole

Take a long cylinder of radius $ a$. It has a long cylindrical hole of radius $b$ parallel to the cylinder axis. The distance between the two axes is $d$. If the cylinder has a uniform current density ...
3
votes
4answers
117 views

Calculate water flow rate through orifice

I'm not very good with fluid physics, and need some help. Imagine the following setup with water contained in-front of a wall with an opening on the bottom: How do I calculate the water flow $Q$?. ...
1
vote
2answers
41 views

Rotational inertia of a ball

This question refers to the solution of problem 12 here. It involves a spherical shell of mass $M$ filled with frictionless fluid of mass $M$ rolling down an inclined plane. (This is problem 12 of ...
0
votes
0answers
22 views

How to find this torque? [on hold]

If I want to calculate the total torque, will it be $\sum$$\tau$$=$ $T_1$$l_1$$-$ $T_2$$l_2$$=$$I$$\alpha$ or $\sum$$\tau$$=$$T_1$$l_1$$-$$(T_2+mg)$$l_2$$=$$I$$\alpha$
0
votes
1answer
34 views

How to find the final momenta of these objects? [on hold]

Suppose two objects collide head on, where initially object 1 (mass $m_1$) is moving and object 2 (mass $m_2$) is stationary. Now assume that they have the same mass, so $m_1 = m_2$. Which ...
2
votes
1answer
135 views

Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
0
votes
0answers
46 views

Variation of the action respect to the metric, integration by parts, variation of ricci tensor [on hold]

Im doing the variation respect to the metric of \begin{equation} S=\int d^4x \sqrt{-g} \{\frac{1}{2} R_{\alpha \beta} A^\alpha A^\beta \} \end{equation} Es decir, \begin{equation} =\frac{1}{2} ...
1
vote
2answers
55 views

Angular momentum for 3D harmonic oscillator in two different bases

I know that the energy eigenstates of the 3D quantum harmonic oscillator can be characterized by three quantum numbers: $$ | n_1,n_2,n_3\rangle$$ or, if solved in the spherical coordinate system: ...
0
votes
1answer
74 views

Specific differential equation in RLC circuit

I have been studying differential equations in RLC circuits: (a generator with fixed EMF $=E$,a capacitor $C$, an inductor with inductance $L$ and internal resistance $r$, and a separate resistor ...
-1
votes
1answer
82 views

How to derive this formula? [on hold]

as far as i know the range of an obliquely projected body which is projected with a velocity of u with some angle $\theta$ with the horizontal under the action of gravity is R=$u^2sin2\theta$/g by ...
0
votes
0answers
25 views

Deriving the Laguerre–Gaussian equation [on hold]

How does one derive the Laguerre–Gaussian equation? $$ x\frac{d^2y}{dx^2}+\left(1-x\right)\frac{dy}{dx}+ny=0 $$
1
vote
1answer
26 views

The dimensional formula of distance travelled in $n$th second

I read that the dimensional formula of distance traveled in $n^{th}$ second is same as that of velocity. Okay, the formula for the distance traveled in $n^{th}$ second is $s_t= u+\frac{a}{2}(2t-1)$ ...
0
votes
1answer
2k views

Electric Field for a hollow sphere with point charge

I think I am over thinking this question: A point charge of $-2\space\mu C$ is located in the center of a hollow sphere. The internal and external radius of the sphere is given by $6.5$ and ...
1
vote
1answer
80 views

Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
1
vote
2answers
321 views

A sphere rolling down a rough wedge which lying on a smooth surface

A sphere of mass $m$ and radius $r$ rolls down from rest on an inclined (making an angle $\phi$ with the horizontal ) and rough surface of a wedge of mass $M$ which stays on a smooth horizontal floor. ...
-1
votes
3answers
69 views

Projectile Motion with air Resistance - Adjust only the Angle to hit a target

OK, let me preface this by saying i am not a physics student, nor have i ever been. I am a software engineer working on a development degree. So this is homework but the assignment was just to create ...
1
vote
2answers
59 views

CPT invariance of Dirac equation

We know that Dirac equation is \begin{equation} ( i \partial _\mu \gamma ^\mu - m ) \psi ~=~0. \end{equation} How can we show that Dirac equation is invariant under CPT transformation?
2
votes
4answers
66 views

Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
1
vote
1answer
70 views

Help with ideal gas law manipulation

Equation 1 represents an improvement over the intial assumption of constant mass velocity (i.e., $\rho v=\rho_o v_o$). We can now improve Eqn. (2) to get to Eqn. (3). My question is: what are the ...
1
vote
0answers
41 views

Defining axes for conservation of energy [on hold]

Problem: A bungee-cord jumper is on a bridge that is $y_1$ above water level $y_2$. The bungee cord obeys Hooke's law with spring constant $k$ and has a relaxed length $L$ The jumper stops before ...
4
votes
1answer
148 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
0
votes
0answers
13 views

How much inductance and capacitance generate in copper strip? [on hold]

I have 60m long copper strip and cross-section area of 25mm x 3mm. and also it has some 90 degree turn after 10m distance. So, How much inductance and capacitance will be generated in strip.? and we ...
25
votes
4answers
4k views

Which ball touches the ground first?

This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes ...
3
votes
2answers
143 views

Error in Standard Textbook “An Introduction to Quantum Field Theory” of Peskin and Schroeder?

On page 191 there is a equation for $D$ given by $$D=x(k^2-m^2)+y(k'^2-m^2)+z(k-p)^2+(x+y+z)i\epsilon. \tag{6.43}$$ With $k'=k+q$ and the constraint $x+y+z=1$. Also $p^2=p'^2=m^2$ and maybe $q=p'-p$. ...
1
vote
0answers
247 views

Fourier Transform of Poisson Equation [migrated]

While trying to solve the Poisson Equation by using Green's Function I have to Fourier transform the equation i.e $$-\nabla^{2}\phi(r)=\rho(r).$$ In the book after Fourier transform, the solution ...
-1
votes
0answers
19 views

Solve the given differential equation by using Green's function method [migrated]

I am really struggling with the concept and handling of the Green's function. I have to solve the given differential equation using Green's function method $$\frac{d^{2}y}{dx^{2}}+k^{2}y=\delta ...
1
vote
2answers
86 views

Finding power with Drag Force equation

The mass of the car is 1500 kg. The shape of the body is such that its aerodynamic drag coefficient is $C_D=0.330$ and the frontal area is $2.50 m^2$. Assuming that the drag force is proportional to ...
0
votes
1answer
321 views

1D Kinematics - Relative Motion involving non-inertial frames of reference

I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
-2
votes
1answer
20 views

Calculate the current in mA which will be flowing through the two resistors [on hold]

Three resistors of 3,4 and 5 ohms are joined in parallel in an electric circuit. If a current of 150mA flows through the resistor of 4 ohms,then calculate the values of the current in mA which will be ...
-1
votes
0answers
41 views

Relative acceleration pulley

Considering If we have pulley with strings on both sides giving different velocities to them, we know velocities of points between them, on diameter, as velocity vector is tangent to it, just ...