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-3
votes
1answer
47 views

Convert an angle

Can someone show me a formula in order to convert an angle from [V] to degree or rad? (i use aPotentiometer measuring steering angle) Edit: Well let me exlpain it. I photo of my experiment is shown ...
0
votes
1answer
50 views

Object Under Resistive Force

An object of mass $m = 5.00 g$ is moving at constant velocity $v_0 = 3.10 m/s$. At $t = 0$ and $x = 1.50 m$, it is subjected to a resistive force $F_{res} = −mbv^2$ where $b = 0.520 m^{−1}$ is a ...
1
vote
1answer
53 views

Block and Pulley Problem with Friction [closed]

1.) What is the acceleration of the hanging mass? (Indicate the direction with the sign of your answer.) 2.) Determine the tension in the cord. (Indicate the direction with the sign of your ...
0
votes
1answer
152 views

Find out the dimension of $\frac{a}{b}$ [closed]

$E=b-\frac{x^2}{at}$ [x=distance,t=time, E=energy] I have tried following but don't know whether I am correct or not $$\frac{x^2}{at}=E$$ $$\frac{L^2}{aT}=ML^2T^{-2}$$ $$a=M^{-1}T^{1}$$ ...
2
votes
0answers
28 views

Double pendulum find first integral [closed]

Consider the following situation of a double pendulum in 2D. We found the moving equations as $$ \ddot{\theta_1}=-L_1\sin\theta_1 + \frac{m_2}{m_1}\cos\theta_2\sin(\theta_2-\theta_1),\\ ...
-1
votes
1answer
37 views

Finding the direction of the electric field of several charges? [closed]

A clock has negative charges -q, -2q, -3q,...., -12q fixed at a the position of the corresponding numerals on the dial. The clock hands do not disturb the electric net electric field due to pont ...
0
votes
2answers
55 views

motion of an electron near a conducting wire [closed]

An electron is ejected from the surface of a long thick straight conductor carying a current, initially in direction perpendicular to the conductor. The electron will: a) ultimately return to the ...
1
vote
2answers
43 views

Why is initial position negative? [closed]

A student on ground throws a ball straight up, the ball leaves students hand with speed of 15m/s when hand is 2.0mm above ground How long is the ball in the air before it hits the ground? I was ...
2
votes
1answer
60 views

Would it really require 44 car batteries to heat my pool? [closed]

After doing some research and math, I 'discovered' that it would take 44 (give or take 20%) car batteries to heat 1,000 gallon pool by 10 degrees. Is this right or am I missing something? It seems a ...
0
votes
3answers
47 views

Clarification on a morin's problem [closed]

What i don't understand is why The solution to this problem says that,$$\tan\theta=\frac{m_{l}}{m_{r}}$$, isn't mass a scalar quantity? The rest is straightforward
0
votes
0answers
47 views

Conditions that the coordinate must satisfy in order to become local inertial

Consider the coordinate transformation $$ \tilde x^a=x^a+\frac{1}{2}\Gamma^a_{bc}x^bx^c $$ I have shown that at the origin $O=(0,0,0,0)$, $$ \frac{\partial\tilde g_{ab}}{\partial\tilde x^c}=0 $$ ...
1
vote
0answers
44 views

Friction force problem for a 4 wheel drive Car [closed]

The car is a 4 wheel drive in equilibrium, the car doesn't touch the ground with the front wheel (A) but is in contact in B with the sidewalk (the sidewalk has a hight equal to $h$), the friction ...
0
votes
0answers
33 views

(Special Relativity) Points that can be seen by an observer

Let the metric be $$ ds^2=(1+gz)^2dt^2-dx^2-dy^2-dz^2 $$ where $g$ is a positive constant. Let an observer be stationary at $x=y=0$ on the surface $z=0$ and look upwards at an angle $\theta$, how ...
0
votes
2answers
51 views

Rocket towing an object

I'm not sure if my question makes sense, but I don't know where to start. A crate of mass $m_2$ is connected by a massless rope of constant length $l$ to a rocket of mass $m_1$. We take into account ...
3
votes
0answers
183 views

Wald problem 4 of chapter 4

I'm trying to derive equation 4.4.51 in Wald's GR book (the second order correction in $\gamma$ term for the Ricci tensor): where $g=\eta+\gamma$. So ...
1
vote
3answers
43 views

Moment of inertia of a cylinder [closed]

When I tried to calculate the moment of inertia ($I_C$) of a cylinder (mass M, height H, radius R) around the rotating axis going symmetrically through its middle, I came up with a different result ...
-2
votes
1answer
45 views

Finding V in a electric field? [closed]

How will we find $V_{ab}$ when $\vec E = (2i+3j+4k)$ N/C , $\vec R_a = (i-2j+k)$ m and $\vec R_b = (2i+j-2k)$ m ? I know $\vec E= -\frac{d V}{d\vec r}$, but I don't know what should be my initial ...
2
votes
0answers
71 views

Calculate the Riemann tensor and Ricci tensor [closed]

Given a metric tensor $\gamma_{ij}$ (where $i, j = 1, 2, 3$; the metric tensor of 3- dimensional space is denoted by $\gamma_{ij}$ to distinguish it from the metric tensor $g_{\mu\nu}$ of ...
0
votes
0answers
27 views

Guides for solving E&M problems [duplicate]

I am an undergraduate physics student in a university and I am looking for a good guide or a handbook with lots of questions and full answers in subjects such as Gauss' law and Maxwell equations to ...
1
vote
1answer
79 views

Expectation value of an operator

Suppose we have: $$ \hat{Q}|\psi_1\rangle=q_1|\psi_1\rangle \\ \hat{Q}|\psi_2\rangle=q_2|\psi_2\rangle $$ with $q_1 \neq q_2$. Then consider the state: $$ ...
0
votes
0answers
44 views

Quick question on Perturbation theory - How do I evaluate this probability?

We know that hamiltonian for interaction between an electron and external field along $z$ is: $$\hat H = \frac{e\hbar B}{2m}\hat \sigma_z = \frac{\hbar \omega}{2} \hat \sigma_z $$ This has energy ...
0
votes
1answer
23 views

Use microwave cavity in atomic clock

In most of the papers regarding atomic clocks, the author talks about a microwave cavity. In this box, all the unwanted frequencies of the electromagnetic radiation are absorbed and the other ...
3
votes
1answer
125 views

Calculating probability current for scattering problem

I'm trying to calculate the probability current for a scattering problem. The potential is $V = V_0 > 0$ in $x>0$, with $E>V_0$ So I have in the region $x \le 0$: $$\psi = \exp(ikx) + R ...
1
vote
1answer
63 views

Calculation of the differential of the entropy

In this review (for those who wants a precise reference see page 8 eq 21), the Author says that: \begin{equation*} S=-\sum_{i}P\left(i\right)\ln P\left(i\right) \end{equation*} and using the ...
-2
votes
1answer
65 views

How does a cyclotron work? [closed]

Doing high school level physics and I got stuck at a question regarding a cyclotron. I need to know how does it work and the reason alternating current is used and the structure of the two semi circle ...
-1
votes
2answers
104 views

Potential at Center of Earth

If using the surface of the earth as a reference point how much work is needed for gravity to pull me to the center. Is it negative infinity or am I wrong? Also is a single value of potential ...
0
votes
1answer
34 views

Leaving a stellar black hole's orbit [closed]

Say Earth is orbiting a black hole 1900 km in diameter, 1.5E33 kg in mass, and has a gravitational pull of 110,858,725,761.77 m/s^2. It's around 40 AU away Earth's orbital speed is 129,305.15664 m/s. ...
1
vote
1answer
63 views

Height of rebound of a projectile from a sphere

My work here is: First, I use conservation of energy: (taking the plane as zero potential) $$\frac{1}{2}m(\frac{2ga}{5})+2amg=\frac{1}{2}mv^2+a(1+\cosθ)mg$$ ...
0
votes
1answer
30 views

Combining ±% with ±dB in measurement uncertainty

Firstly apologies if this is not the correct place to post this but wasn't sure which site would be good to ask regarding about measurement uncertainty calculation. I am trying to calculate the ...
0
votes
2answers
33 views

Projectile motion - ball hit 180m/s at 45 degrees, what is the hang time? [closed]

Assuming no air resistance etc, how long is the ball in the air for? This is actually part of a longer question concerning the ball trajectory on different planets but I think there must be an easier ...
2
votes
0answers
33 views

Laplacian in 4 spatial dimensions; 4th dimension warped

How can I prove the form of the Laplacian in four spatial dimensions, using the identification $y = y + 2\pi R$ for the fourth dimension and assuming the others as the usual Cartesian ones? I want to ...
1
vote
1answer
29 views

Finding the equation of motion regarding a block pulling a uniform disk [closed]

My problem is finding the equation of motion for the block. Using Newton's Second Law, I did: $$4g-T-R=4\frac{dw}{dt}$$ But the mark scheme says: $$4g-T-R=0.2*4\frac{dw}{dt}$$ And I don't understand ...
1
vote
0answers
28 views

Quick question on convolution - Diffraction through a pair of slits

We know that the fourier transform of the amplitude function (in terms of $y$) gives you the amplitude function (in terms of $\theta$) Consider a pair of triangular slits: Fourier transform of ...
1
vote
0answers
12 views

Coarse-graining on a second channel decreases mutual information?

Let $X_1,B_1,X_2,B_2$ and $Y_1,A_1,Y_2,A_2$ and $C_1$ and $C_2$ be binary random variables. Suppose: $I(X_2:B_2|C_2=0)+I(Y_2:A_2|C_2=1) \leq 1$. This can be thought of as a bound on the capacity ...
0
votes
1answer
41 views

proportion of solar radiation that reaches the earth surface

I have been following the methods suggested by members of this site to calculate the solar irradiance outside of the earth's atmosphere, see here. I now want to calculate the solar irradiance ...
1
vote
1answer
43 views

Travel time for accelerating object [closed]

I have an object which starts at velocity = 0. Accelerates to a known max speed and continues thereon at constant velocity (max speed). My problem: How long does it take to reach a known ...
1
vote
1answer
52 views

Equation of state not linear in energy or system size

Which of these two equations of state are valid? $$S_1 = L_0 \gamma (\theta E/L_0)^{1/2} - L_0\gamma\left[\frac{1}{2} \left(\frac{L}{L_0}\right)^2 + \frac{L_0}{L} - \frac{3}{2}\right]$$ $$S_2 = L_0 ...
2
votes
3answers
67 views

Elastic collision of point particle and rod

A 1 meter long rod on the ice with mass $m_2=1$ kg is perpendicularly hit on one end by a point particle with mass $m_1=0.1$ kg. The collision is elastic and the point particle is bounced back in ...
1
vote
1answer
45 views

Derive force from the pair-wise potential equation [closed]

How can we calculate the force exerted on particle $i$ by particle $j$ given a general potential function $V(d)$? Let's discuss this genenal question with a concrete example below. To simulate the ...
1
vote
0answers
29 views

Calculating a spacecraft's deflection angle [closed]

There is a spacecraft with mass $M_1$ moving in a certain trajectory with a constant speed $V_r$. To modify its trajectory, a engine is turned on and starts ejecting gas at a speed $V_g$, which is ...
2
votes
1answer
76 views

Does the average momentum vanish for an eigenstate of the simple harmonic oscillator?

Suppose we have a simple harmonic oscillator, let's consider the ground state, $|0\rangle$ and the first excited state $|1\rangle$. $\langle 0|\hat p|0 \rangle$ is zero right? Since the particle can ...
1
vote
3answers
232 views

Why is using Newton's First Law failing me?

A factory worker pushes a 29.7kg crate a distance of 5.0m along a level floor at constant velocity by pushing downward at an angle of 32$^\circ$ below the horizontal. The coefficient of kinetic ...
0
votes
0answers
51 views

Circuit analysis, calculating voltage across resistor [duplicate]

i'm solved this question, I'm sure that solution is right, but my instructor says that V1=116V, and also he said that he will not show how he get this result.Please help to identify who is right.
1
vote
0answers
32 views

Deriving tensor in Euler's equations for rigid body rotation

The answer to physics.stackexchange.com/questions/104513 gives the following derivation of tensor $I$: $\begin{align} \frac{\text{d}}{\text{d}t} I &= \frac{\text{d}}{\text{d}t} ...
1
vote
1answer
58 views

Finding out the Potential difference

Find the potential inside and outside a uniformly charged solid sphere whose radius is $R$ and whose total charge is $q$. Use infinity as your reference point. Compute the gradient of $V$ in each ...
1
vote
0answers
30 views

Lagrangian for a system of particles [closed]

If a system of particles attracting each other under inverse square force, then prove that $$ 2<T> + <V> = 0.$$
2
votes
1answer
59 views

Relation between electric potential and wavelength of an electron

"An electron that is accelerated from rest through an electric potential difference of $V$ has a de Broglie wavelength of $\lambda$. Investigate the relationship between $V$ and $\lambda$." I had two ...
0
votes
2answers
60 views

force of hail falling straight

There is a hail storm and it's falling straight down (0 wind factor) will the hail meet a moving car with greater force than a car standing still?
0
votes
2answers
79 views

Quick question on astronomical units

I'm trying to solve for $\frac{M*}{M_0}$ and $p''$ using these two equations: Here is the lecturer's working, I worked it out several times and I got a different answer! Surely when you use ...
0
votes
1answer
41 views

Electromagnetic wave in a medium with $\sigma \ne 0$ [closed]

I want to prove that the reflectancy of an Electromagnetic wave in a medium with $\sigma$ $\ne$ 0 is: \begin{align*} R_{\|}=R_{\perp}=\frac{(n-1)^2+k^2}{(n+1)^2+k^2} \end{align*} any advice, please? ...