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0
votes
2answers
26 views

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), ...
-3
votes
0answers
12 views

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 ...
1
vote
0answers
43 views

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 ...
0
votes
0answers
22 views

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.
-2
votes
0answers
27 views

Particle Acceleration in three dimensions [on hold]

So here is the problem I dont know how to approach it.
-2
votes
0answers
15 views

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 & ...
2
votes
1answer
55 views

H-theorem and Boltzmann equation applied to Boltzmann distribution

Using the Boltzmann equation: $$ \frac{dH}{dt} = \int_0^{\infty} dr \int_0^{\infty} ds W(r,s)[p_r - p_s][\ln{p_r} - \ln{p_s}]$$ and assuming $p_r = e^{-\beta r}$, the equation looks like $$ ...
1
vote
1answer
338 views

How fast must a torus spin to have a felt gravity? [on hold]

Given a rotating torus (like a gyroscope or a rotary) with a radius of 1km, how fast must it rotate to have someone inside the torus feel normal gravity of 1G?
4
votes
1answer
80 views

Conservative Vector Fields

I was always told that to find whether or not a vector field is conservative, see if the curl is zero. I have now been told that just because the curl is zero does not necessarily mean it is ...
1
vote
1answer
63 views

Question about torque and center of mass [duplicate]

If a yo-yo's string is not attached to anything and the yo-yo is dropped, it is obvious it will fall at $g$. In this scenario, Tension of string = 0. If a yo-yo's string is attached to a cieling and ...
17
votes
5answers
4k views

Is this scene from the A Team explainable by Physics?

This scene (youtube link) from the movie The A-team, the four members are in the tank and its falling from the air, they fire the canon and it slows the tank from falling for a moment before falling ...
0
votes
0answers
26 views

A vector field $\vec{F}$ from cartesian to spherical [closed]

I have a vector field F that has the same magnitude and directions at all points in space. If I choose $z$-axis parallel to $\vec{F}$, so the cartesian coordinate of $\vec{F}$ is $\vec{F}=F\hat{z}$, ...
-1
votes
1answer
66 views

Navigating a Time Machine

Notes: The background for this question is working out details of a sci-fi story. Answers to the effect of "time travel isn't possible" or "FTL isn't possible" are therefore not helpful. I'm looking ...
0
votes
1answer
65 views

Time Dilation Problem [closed]

I'm having some trouble using the time dilation formula. Say an astronaut leaves Earth for 10 years, at 0.85c. How much time has passed according to an observer on Earth? I tried using the ...
-2
votes
0answers
30 views

Passing a Car With known speeds vs. Time [closed]

While driving, it takes 22.0 s to pass a car. If my speed was 64.0 mph when I started to pass, and was 80.0 mph as I finished, how far (in feet) did I travel while passing?
2
votes
2answers
58 views

Calculating coefficient of friction

Consider a body attached to a horizontal spring and resting on a surface, inclined at an angle $\theta$ from the ground. The spring constant is $k$. Initially the spring was kept in its ...
0
votes
0answers
27 views

Vehicle crash analysis from trajectory of vehicle [closed]

A rear-wheel driven large sedan, weighing $4 ,120$ lbs, with a $10¼$-foot wheel base, traveled up an inclined ramp of $11$ degrees. The vehicle left the ramp at $22$ mph, traveled through the air ...
0
votes
1answer
27 views

The vector r points from $P'(x',y',z')$ to $P(x,y,z)$ [closed]

For some reason this question is giving me a hard time :( The vector $r$ points from $P'(x',y',z')$ to $P(x,y,z)$. (a) Show that if $P$ is fixed and $P'$ is allowed to move, then ...
1
vote
2answers
17 views

Projectiles Launched at an Angle with unspecified Initial Velocity [closed]

I'm attempting to do my Physics homework, and I did the first one right, but that problem gave me initial velocity. This problem gives me only the angle relative to horizontal and the distance it ...
-2
votes
1answer
34 views

Projectile with air resistance [duplicate]

If you have a projectile with these variables. $x_0 = 1v_{0x} = 70, y_0 = 0, v_{0y} = 80, a_x = 0, a_y = -9.8$ I know how to plot these points with this equation. $$ x = x0 + (v_{0x})t + 1/2((a_x)t^2) ...
0
votes
0answers
46 views

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 ...
0
votes
0answers
35 views

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: ...
0
votes
0answers
26 views

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 ...
1
vote
0answers
51 views

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 ...
1
vote
0answers
19 views

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?
-1
votes
0answers
20 views

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 ...
-1
votes
1answer
24 views

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 ...
0
votes
2answers
35 views

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 ...
0
votes
1answer
40 views

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 ...
2
votes
0answers
40 views

Steady-state adiabatic nozzle, unknown exit velocity & temperature [closed]

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. ...
0
votes
2answers
52 views

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 ...
0
votes
1answer
120 views

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 ...
0
votes
0answers
36 views

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 ...
1
vote
0answers
50 views

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 ...
-1
votes
1answer
32 views

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.
0
votes
0answers
24 views

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 ...
0
votes
0answers
38 views

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 ...
0
votes
1answer
22 views

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 ...
0
votes
0answers
133 views

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 ...
-1
votes
1answer
40 views

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) ...
0
votes
2answers
51 views

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 $2m$ ...
-2
votes
2answers
56 views

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 ...
0
votes
1answer
77 views

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 ...
1
vote
2answers
41 views

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 ...
0
votes
0answers
28 views

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 ...
3
votes
1answer
148 views

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 ...
2
votes
0answers
85 views

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 ...
3
votes
3answers
86 views

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} ...
1
vote
1answer
70 views

Finding the magnetic vector potential by calculus of variations

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 ...
2
votes
1answer
108 views

Add air resistance to projectile motion

I am given an initial x and y position and initial velocity and I was asked to graph the trajectory in 1 second intervals. This is what I have so far: If $x_0 = 1, v_{0x} = 70, y_0 = 0, v_{0y} = 80, ...