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.

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3 views

Capacitance between multiple conductors

So, I am having trouble figuring out the capacitance of systems like these( 3 parallel wires) First and third are connected so their potentials are the same, and since their radiuses are also the ...
0
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0answers
19 views

Negative Feedback

In the circuit in figure below the narrow resistor is made of the same material as the thick connecting wires. (a) Sketch a graph of the electric field’s magnitude at different locations. (b) ...
0
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1answer
19 views

Friction Force and Applied Force for Acceleration [on hold]

A person needs to move a 565 N object. The coefficient of static friction for the surface it's sitting on is 0.63. How much force is required to accelerate the object at an initial rate of 0.4 m/s2? ...
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0answers
38 views

Problem with commutator [on hold]

My area is mathematics; however, told me about a problem that can solve with simple math, it says: Using $[\hat{J_{z}},\hat{O}]$, show that $\langle\alpha,j,m|\hat{O}|\beta,j',m'\rangle$ can be ...
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0answers
16 views

Principle of electrical machine by vk R mehta complete ebook needed [on hold]

I need the ebook for my exam on Wednesday(expecially dc generator and dc motor chapter)
2
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2answers
20 views

Wave displacement with phase difference 180

The variation with distance x along a wave of its displacement d at a particular time. A second wave has the same frequency and speed as the wave shown in Fig. 2.1 but has double the intensity. The ...
1
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1answer
22 views

a charged particle path [on hold]

A particle of mass $m$ and charge $e$ enters a homogeneous and stationary electric field $E$ with velocity $v_0$ perpendicular to the direction of the field. Calculate the particle's path? What does ...
2
votes
1answer
44 views

Finding potential energy of a solid hemisphere on top of another solid hemisphere [on hold]

A solid hemisphere with radius $b$ has its flat surface glued to a horizontal table. Another solid hemisphere with radius $a$ rests on top of the hemisphere of radius $b$ so that the curved ...
0
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0answers
36 views

2 masses are attached to hanging string and one is released. What is the max height reached by the other?

A spring is in static equilibrium (not moving) with two masses ($m_1$ and $m_2$) attached to the spring. The spring constant is: 22.0 N/m, while $m_1 = 0.16\,kg$, $m_2 = 0.13\, kg$ and mass 1 ...
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0answers
33 views

Projectile motion, solved with perturbation theory [on hold]

A ball is dropped from rest, the initial height is $h_1$. There is air resistance given by $-mkv$. In the downward motion, the equation of motion can by written as $$\dot v = -g-kv$$ with the y ...
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0answers
19 views

Finding most/least tension between 5 cars attached to a train [on hold]

I am currently doing Grade 11 physics and I have been troubled by this one question for homework for quite a while. Hopefully most of you will be able to help me out. Question: A 40,000kg train ...
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0answers
23 views

Calculate the density of this liquid and determine general formula for finding density of a liquid [on hold]

a) A 3.8 kg aluminum ball is found to have an apparent mass of 1.9 kg when completely submerged in a particular liquid. Calculate the density of the liquid. b) Determine a general formula for ...
1
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4answers
253 views

Having trouble understanding some stuff about delta functions [on hold]

I was going through one of the examples in Griffith's Quantum book and there was a few things in Example 3.3 that I didn't understand that I was hoping to get some clarification on. For instance, we ...
0
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2answers
26 views

Finding the initial velocity of a vertical circular motion [on hold]

A particle P is suspended from a fixed point O by a light inextensible string of length a. When hanging at rest under gravity at A it is given a horizontal velocity u. The particle moves freely ...
0
votes
1answer
37 views

Tangential velocity of a parabola

For an experiment on the parabola motus we decided to calculate the velocity of the object thrown in three phases: When the object leaves the spring that throws it (we solved it using conservation ...
0
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0answers
21 views

Batteries connection to get maximum intenisty [on hold]

The question states: There are 72 batteries, each of which has a 1.5V and the internal resistance of each is 1 Ohm. The external resistance is 3.5 Ohm. What is the maximum intensity that we can ...
6
votes
3answers
669 views

The physics behind Balloons lifting objects?

Apologies for the super basic question, but we all have to start somewhere right? Can somebody please explain exactly how you would calculate the number of helium balloons it would take to lift an ...
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0answers
13 views

How to drive quadrotor moments of inertia

I would like to know how moments of inertia (i.e. around x,y and z axes) of a quadrotor is driven given the total mass and the distance from the origin of the quadrotor to the center of a $i$th ...
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0answers
16 views

A box up an inclined ramp with a coefficient of friction [on hold]

A 6.25 horsepower motor to pull the boxes a distance of 8.35 meters up a ramp inclined at an angle of 36.2º with respect to horizontal. The boxes have a coefficient of kinetic friction of 0.381 as ...
1
vote
2answers
54 views

Is a double integral required to find the moment of Inertia of a non-uniform sphere?

Consider some ball of given radius $R$, with a mass density function that depends on the radial variable, $\rho=\rho(r)$ where $r$ is the distance from the center of the sphere. What is the moment ...
0
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0answers
8 views

What is the force of the wind resistance? [on hold]

A sled of mass 15.0 kg is pulled forward with a force of 35 N. Also a frictional force of 12.2 N acts on the sled. Finally a wind resistance acts on the sled. Over a period of 18.0 s the sled ...
6
votes
2answers
85 views

Two carts connected by spring on frictionless track

I have the following homework problem: Consider two carts of equal mass m on a horizontal, frictionless track. The carts are connected by a single spring of force constant k, but are otherwise ...
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2answers
36 views

Flea jumping question [on hold]

During takeoff, a flea develops an acceleration of $3m/s^2$. It reaches a max height of 36mm. How long does this acceleration last? Finding the initial velocity was fairly easy, but finding the time ...
0
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0answers
18 views

Projectile Aiming [on hold]

I'm having a but of trouble with a game I'm programming. What I have is an enemy who periodically shoots a laser at the player if they're close enough. I've been trying to come up with a way to make ...
1
vote
1answer
39 views

Hooks Law and acceleration [on hold]

A 435 gram sharpened piece of iron rebar into a spring loaded device. It takes a force of 355 Newtons to compress the spring by 27.5 cm. With what speed does the rebar shoot out of the device? ...
0
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3answers
42 views

Determine which circuits are parallel and which are in series

I need to find the Equivalent Resistance across A and B. The problem is, I don't know which one's are in series and which ones are in parallel. How do I identify which ones are parallel or series?
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0answers
15 views

Uniform motion - need help with this problem [on hold]

Body A is moving towards body B (which is moving to A) with speeds v1 (for A) and v2 (for B) on the road s.Body B starts moving after time Δt compared to the body A (so t2 = t1 + Δt).I want to know ...
2
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2answers
775 views

These two operators commute…but their eigenvectors aren't all the same. Why?

The Hamiltonian $$H = \left[ \begin{array}{cccc} a & 0 & 0 & -b \\ 0 & 0 & -b & 0\\ 0 & -b & 0 & 0\\ -b & 0 & 0 & -a \end{array} \right] $$ commutes ...
0
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0answers
28 views

A flight attendant on a plane - special relativity problem [on hold]

the question goes like this: on a plane, flying at 0.8c which is 100m long (in plane system), at the back of the plane there is a flight attendant moving at 0.55c (relativitly to the plane system). ...
0
votes
1answer
23 views

Determining energy stored in capacitor and inductor in RLC circuit

I've been stuck on the following homework problem for a few hours now with little progress. As you can see, it's a relatively simple RLC circuit with a couple independent sources and a ...
-1
votes
1answer
31 views

Question about a spring-mass-damper [on hold]

The following diagram shows the problem I have. The equation I derived using Newton's second law is also shown in the figure. M is the mass of the object the system is attached to and needs to be ...
-1
votes
0answers
24 views

What is the mass of the unstable particle? [on hold]

Consider a massive particle at rest. This particle is unstable and decays into three massless particles: the first and the second are moving at right angles to each other and have 100 GeV energy ...
0
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1answer
38 views

Calculating the induced emf without knowing the change in magnetic flux [on hold]

A conducting rod of length $\ell$ moves on two horizontal frictionless rails, as in Figure P20.30. A constant force of magnitude 1.00 N moves the bar at a uniform speed of 2.00 m/s through a ...
-3
votes
0answers
113 views

How to find the moments of A and B [on hold]

1) A 4.5m beam of weight is 1200N, supported by two points pivots A and B. A is x metres(m). Determine x, given that B is twice A
0
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0answers
34 views

Quantum Mechanics: Eigenstates for Quantum operators [on hold]

1. The problem statement, all variables and given/known data Suppose that a state |Ψ> is an eigenstate of operator B, with eigenvalue bi. 2. Relevant equations i. What is the expectation value of ...
2
votes
0answers
50 views

How to compute the normal ordered angular momentum of a Klein-Gordon real scalar in terms of ladder operators?

I'm trying to compute the angular momentum $$Q_i=-2\epsilon_{ijk}\int{d^3x}\,x^kT^{0j}\tag{1}$$ where ...
0
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0answers
19 views

Heavy beam suspended by nylon and steel cables, angle problem [on hold]

I'm having trouble with the following simple physics problem: A heavy uniform beam of mass 8000kg and length 2,0m is suspended at one end by a nylon rope of diameter 2,5cm and at the other end by a ...
0
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0answers
27 views

Forces exerted on legs of a table

This is actually for a computer science homework problem, but I haven't studied any physics in five years so I'm having a bit of trouble. I'm given a table of three legs with their coordinates and I ...
1
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1answer
31 views

Proportionality and units

This might be very easy, but I'm not 100% sure how it's done. Lets say I have this equation: $$R = R_{0} \cdot \left[1 - \frac{P_{0}R_{0}}{GM_{0}\rho_{0}}\right]^{-1},$$ where I know $P_{0}$, ...
4
votes
2answers
217 views

Position operator in QFT

My Professor in QFT did a move which I cannot follow: Given the state $$\hat\phi|0\rangle = \int \frac{d^3p}{(2\pi)^3 2 E_p} a^\dagger_p e^{- i p_\mu x^\mu}|0\rangle,$$ he wanted to show that this ...
0
votes
0answers
14 views

Electric field due to continuous volume charge distribution [duplicate]

Since the Electric field at point (0,0,z) is $$dE = \frac{\rho vdv}{4\pi\epsilon_0R^2}\hat{R}$$ $$\hat{R} = \cos\alpha \hat{z} + \sin\alpha \hat{\rho}$$ where $\hat{R}$ means unit vector $R$. ...
0
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0answers
11 views

Find the current/potential difference across each bulb [on hold]

I need help solving this problem: Two identical bulbs are connected in parallel to a different source, one with E = 8.0 V and internal resistance 0.8 ohm. Each light bulb has a resistance R = 2.0 ohm ...
0
votes
0answers
28 views

Calculating the distance that a telescope can detect [on hold]

A typical 4-meter telescope is capable of detecting stars with apparent magnitude of +24 with an exposure time of 5 minutes. Using this exposure time, out to what distance (in pc) can this telescope ...
0
votes
1answer
13 views

Compute convective heat transfer coefficient for a condensing steam

I have a question about convective heat transfer coefficients. I am trying to figure out how much steam I can condense in this specific heat exchanger. Steam at 9 MPa is condensed in a 1 shell pass, ...
0
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0answers
23 views

Circuit Diagram [on hold]

Three resistor are put into play, two in parallel and another in series to them. One of the resistors in parallel is decreased. what will happen to the voltage and current.
0
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0answers
27 views

Electric Field due to volume charge [on hold]

Electric Field at point P due to volume charge Since,the Electric field at point (0,0,z) is dE = ρvdvaR/4πε0R2 aR = cosα az + sinα aρ where aR means unit vector R can anyone derive the above ...
0
votes
0answers
35 views

Dry Ice Sublimation time, practical calculations [on hold]

I would like to send a parcel to a family abroad with frozen (to the temperature of -18 ° C.) products.The products are small balls having a diameter of 4 cm. Balls are made from pizza dough.Total ...
0
votes
0answers
42 views

An inclined pulley system [on hold]

M1 and M2 both are 400g. There is no friction and the pulleys are massless. I am trying to work out the acceleration on M2. I am unsure whether the acceleration should be: $a\space =Mg\space -\space ...
0
votes
1answer
58 views

The “classical radius” of the electron [on hold]

According to one theory, the mass m of the electron arises simply as a consequence of the electrostatic energy of its electric field, through Einstein's famous expression ε=mc^2, where ε is the field ...
2
votes
1answer
36 views

entropy of a long molecule chain with respect to its length

Consider a (very long) one-dimensional chain of $N$ moleculs, which can be in either of the energy states $\alpha$ or $\beta$. The configurations have length $a$ or $b$ respectively. Show ...