# Tagged Questions

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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### Is in this case distance same as displacement? [on hold]

I have this graph, and I need to know the displacement in the interval from 0 to 5 seconds, so I found the area of the rectangle that you can see there. A = w*h, which means X = (5 seconds)*(20 m/s), ...
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### Oscillation and wave [on hold]

A box of mass $0.2 \,\text{kg}$ is attached to one end of a spring whose other end is fixed to a rigid support. When a mass of $0.8 \, \text{kg}$ is placed inside the box, the system performs four ...
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### Help with parametrization of surface if I'm given the metric [on hold]

I've got a homework question. Consider a 2 dimensional space with metric $$ds^{2} = \frac{dr^{2}}{1 -\frac{2}{r} } + r^{2}d\theta^{2} .$$ I need to show that this is the induced metric ...
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### How does this series expand the expression? [migrated]

How does $$\sqrt{R^2 + |x|^2} = R + \frac{|x|^2}{2R}+\dots$$ when expanded around the point $x=0$? I tried using a Taylor expansion but it didnt work out.
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### Particle Acceleration in three dimensions [on hold]

So here is the problem I dont know how to approach it.
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### Find acceleration along normal and tangent [on hold]

A small block can move in a straight horizontal line a along AB. Flash lights from one side projects its shadow on a vertical wall which has horizontal cross section as a circle. Find tangential & ...
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### How far will the stone travel in 2.0 s? [closed]

A stone is thrown vertically down from the top of a 40 story building with an initial speed of 1 m/s. How far will the stone travel in 2.0 s? the answer is 22 m and my answer is 17.6 m I used this ...
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### Calculating M squared [closed]

I have a laser beam which has a wavelength of 1064nm. The beam quality is 12 mm mrad (SPP). The diameter of the beam is 10 mm. I was told to calculate: $$M^2$$ I used this formula: ...
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### Calculate temperature at isobaric or isochoric process [closed]

I've had some trouble in regards to calculate the temperatures in the different states. Considering the following pV-diagram: Here is the data I have: The adiabatic constant $\gamma$ is 1.4 ...
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### Projectile Motion Equation - Understanding this Formula [closed]

I don't understand why this formula is relevant to the problem: This was the relevant worked solution: My problem is that I do not understand this formula because I don't even understand what ...
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### Collision (work energy and power) [closed]

A ball is allowed to fall from rest on a horizontal floor from a height of 10m If there is 20% loss of energy due to impact then after one impact ball will go upto?
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### How can I determine the magnitude of an electric field based off of the magnitude of a dipole in the field? [closed]

Point charges q1=− 5.00nC and q2=+ 5.00nC are separated by a distance of 3.50mm , forming an electric dipole. The torque exerted on the dipole has a magnitude of 7.60*10^-9 N*m at an angle of 37∘ with ...
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### Spring launches a mass on an incline plane with friction, find the height [closed]

So I've calculated the answer to this problem, but my answer is different from my book's, so I'm trying to find the error. A spring with coefficient $k=600N/m$ launches a mass of $1.2kg$ from an ...
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### Find net force on a mass centered between four other masses

I'm not going to post the full question, I just want a general idea of how I should go about solving this type of problem. There is a square with 4 charged masses on each of the corners, in the ...
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### A pendulum's rope swings and strikes a peg [closed]

So I have this problem, as far as I can tell I solved it correctly, and it's not equal to any of my answer choices. The problem is: A rope of length $L$ is attached at one end to a ceiling and at ...
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The question is 2.10 taken from: Introductory Chemical Engineering Thermodynamics, 2E by Elliot,Lira Air at 30ºC and 2MPa flows ata steady state in a horizontal pipeline with a velocity of 25m/s. ...
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### A problem says : a car starts from rest and undergoes a constant acceleration. It travels 5 m in the…? [closed]

A problem says : A car starts from rest and undergoes a constant acceleration. It travels 5 m in the t interval 0 s to 1 s, find the displacement of the car during the time interval from 1 s to 2 ...
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### From Paris to … London [closed]

(Excuse the pun in the title, couldn't resist) Paris and London are connected by a straight underground tunnel, as shown in the diagram below. A train travels between the two cities powered only by ...
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### Capacitance changes by a factor of 3 or 9?

This is an example problem with solution in a book I am reading on electrostatics. "We have two square parallel plate capacitors with length $a$ and separation $d$ with $d<<a$. If we triple ...
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### Equation regarding the Riemann tensor in the Cartan formalism [closed]

I have a problem verifying the following equation (in three dimensions) $$\epsilon_{abc} e^a\wedge R^{bc}=\sqrt{|g|}Rd^3 x$$ where $R$ is the Ricci scalar and $R^{bc}$ is the Ricci curvature ...
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### Electric Field of a sphere

Is there a point in space where the electric field is half of the electric field on the surface of the sphere? I just got curious if it would be possible.
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### Help solving 2D motion problem [closed]

I have the following 2D motion problem: A sprinkler mounted on the ground sends a jet of water at a 30 degree angle to the horizontal. The water leaves the nozzle at a speed of 12 m/s. How far ...
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### Nuclear Interaction Stopping Power

Hello again question board. I'm in need of some help with my b) question for homework I have. Following question is verbatim: "How thick should a wall of shielding iron be to absorb a 10 GeV/c pion ...
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### Comparing work done for two accelerations

Suppose at a time $t_{0}$ a car goes from 0 to 30mph at time $t_{1}$, and then maintains a speed of 30mph until $t_{2}$. After that minute it accelerates, reaching 60mph at time $t_{3}$. I want to ...
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### kinematics question about runner [closed]

Here's the question: Your goal is to complete your 10,000-m run in less than 30.0 min. Apparently you've started too slowly because at 27.0 min, you still have 1100 m to go! You can accelerate at ...
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### How do you find the average speed and average velocity? [closed]

The shuttle craft "Galileo" travels at a constant velocity of $2.73*10^3$ m/s up for $34.0$ min. and then turns around to travel $1.45*10^3$ m/s down for $15.0$ min. a) Find its average speed. b) ...
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### A spring with two masses in an inelastic collision

An ideal spring is attached to a wall, and the other end is attached to a mass $m$. The spring is initially compressed a distance $x$. After it is released, the mass collides with another mass $2m$ ...
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### Rabbit and tortoise in a foot race [closed]

A rabbit (H) and a tortoise (t) are in a foot race. When the tortoise is 22 m from the finish line, he has a speed of 4.0 m/s but is 5.0 m behind the rabbit. The rabbit has a speed of 5.0 m/s. The ...
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### How much energy is necessary to set a year to exactly 360 days

How much energy would be necessary to slow down Earth rotation such that a year was 360 days long? In the same spirit: how much energy would be necessary to make the Earth rotate faster around the ...
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### Finding the current in a parallel circuit [closed]

Two resistors are joined as shown. The top resistor receives a current of 3 A. What is the current in the other resistor? What is the current that enters at junction A? I'm confused on how the two ...
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### Calculus of variations applied to a rotating liquid

I thought I knew how to use calculus of variations, but then I started thinking about the problem of a rotating liquid and it confused me a great deal. It would be nice to hear your thoughts on the ...
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### How is weight distributed when legs are astride?

Is there a simple and quick formula to find the weight (the force acting) on each leg, especially when legs are astride and they are not equally stretched? (or, better) not equally distant from the ...
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### Hoop rolling inside a circular hole

A hoop of radius $b$ and mass $m$ rolls without slipping within a stationary circular hole of radius $a > b$ and is subject to gravity. Use the generalized coordinates the rotation angle $\phi$ of ...
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### How to prove the Levi-Civita contraction?

I want to prove the following relation \begin{align} \epsilon_{ijk}\epsilon^{pqk} = \delta_{i}^{p}\delta_{j}^{q}-\delta_{i}^{q}\delta_{j}^{p} \end{align} I tried expanding the sum \begin{align} ...
Given the functional $$F[A]=\int_{\mathbb{R}^3}\{\frac{1}{2\mu(x)}|\nabla\times\vec{A}|^2-\vec{J}\cdot\vec{A}\}d^3x$$ with $\vec{A}$ is a candidate vector potential for the field ...