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.

learn more… | top users | synonyms (1)

-1
votes
1answer
258 views

Properties of expectation values of quantum operators [closed]

$$\langle \hat A \rangle \langle \hat B \rangle=\langle \hat A\hat B \rangle,$$ $$\langle \hat A \rangle + \langle \hat B \rangle=\langle \hat A + \hat B \rangle,$$ $$\langle \hat A^2 \rangle ...
-1
votes
1answer
140 views

How to find replacement function of a mass?

I wonder how I can find the replacement function of the center of the blue mass? The center of mass of the blue mass is $(0,0)$ and the blue mass is homogeneous. The masses do not move at t=0 in the ...
-1
votes
1answer
86 views

I think there is a mistake in solutions to this problem. plus and minus sign

! I pretty much had what the solutions had, but we disagreed with one thing, a minus sensitive sign. $\sum W = \Delta K$ $\int_0^{-s} - ks^2 ds = \frac{ks^3}{3} = \frac{1}{2}m(v^2-4^2)$ ...
-1
votes
1answer
568 views

How should I draw this free-body diagram?

The horizontal force P acts on the rim of the homogeneous cylinder of radius R and weight W. Determine the smallest coefficient of static friction that enables the cylinder to start rolling up the ...
-1
votes
2answers
3k views

Finding initial velocity using conservation of momentum and energy [closed]

A 14 g bullet is fired into a 120 g wooden block initially at rest on a horizontal surface. The acceleration of gravity is 9.8 m/s^2. After impact, the block slides 6.97 m before coming to rest. If ...
-1
votes
2answers
369 views

A proton is trapped in an infinitely deep well of L meters. The proton is in the first excited state. How does the excited state change the question.

The real question was: A proton is trapped in an infinitely deep well of 1*10^-14m. I suppose that is unimportant as that should only help us decided the limits of our integration. What I'm worried ...
-1
votes
1answer
551 views

How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates?

How do I express the Kepler general orbit $r(\phi)$ in rectangular coordinates? I use the identities $x=r\cos\phi$, $y=r\sin\phi$, and $r^2 = x^2 + y^2$, but I block at some point.
-1
votes
1answer
145 views

Radiation dosage problem [closed]

A large room is filled with air polluted with Caesium-137 at an average density of 1 Cs-137 particle per $\text{cm}^3$. A human is sitting inside the room for duration of $T$. What is the total energy ...
-1
votes
1answer
431 views

Acceleration Force [closed]

A 6500-kg helicopter accelerates upward at 0.60 m/s² while lifting a 1200-kg car. (a) What is the lift force exerted by the air on the rotors? (b) What is the tension in the cable (ignore its mass) ...
-1
votes
0answers
22 views

How do I know which force to use in moments calculation?

I'm working on some Statics problem, with the method of joints, etc and for all of them, we use sum of moments = 0. However, I'm very confused about which forces I should use to find the sum of ...
-1
votes
0answers
24 views

Trying to calculate the average speed from this question [on hold]

I already checked the average speed question that was posted before and tried applying the methods to my question but nothing seemed to work. I would like to know if anyone can explain to me how to ...
-1
votes
0answers
39 views

Moving object under water [on hold]

If a cube of side 20ft is at 50 ft below in fresh water and it extends 20 feet horizontally giving it a measurement of 20 ft high, 40 ft long by 20 ft wide and the moving section weighs 700lbs. How ...
-1
votes
0answers
24 views

Kinematics of point moving on a circle [closed]

Let $A$ be a fixed point on a circle. Let a point $P$ move along the circle in such a manner that the acceleration vector always points to $A$. Show that the acceleration is proportional to ...
-1
votes
0answers
10 views

Volume change of rod under loading given Poisson's ratio [closed]

I would usually use a combination of the following equations to solve these type of problems: But not sure how to calculate volume change as I am not given any lengths such as diamter, ...
-1
votes
0answers
15 views

Spherical Trigonometry Question [migrated]

Given that $\cos(\lambda) = \sin(\delta)\cos(\epsilon)-\cos(\alpha)\cos(\delta)\sin(\epsilon)$ Can you solve for $\delta$?
-1
votes
1answer
22 views

Masses and Pulley

I have a two mass and a pulley system as shown here: I have the following two questions: First, why does $\dfrac{d^2}{dt^2} y_p$ is not zero, i I mean I don't understand why does $ y_p$ is going to ...
-1
votes
1answer
48 views

Calculations with operators - Proof: Equation of Operators [duplicate]

I have a problem in Quantum mechanics 1 with Operators. I have to prove the following equation. I tried it for about 4 hours without any result: Condition: $[[\hat A,\hat B],\hat A]=[[\hat A,\hat ...
-1
votes
1answer
43 views

Initial velocities of a collision [closed]

This is the question: A car of mass 900 kg and a van of mass 1300 kg collide at a crossroads. Investigation into the collision discloses that the car was travelling south east and that the van was ...
-1
votes
1answer
59 views

Determine the maximum capillary rise

The problem I have is this: A capillary tube is immersed vertically in water. Knowing that water starts to evaporate below 2kPa, determine the maximum capillary rise and tube diameter. Assume the ...
-1
votes
1answer
40 views

Finding dimensional formula

$$y(x,t)=2A\sin(Kx)\cos(\omega t)$$ $A$ and $x$ are in metre, $\omega$ is angular frequency. Then find dimensions of $A$ and $K$. In this equation how can I find the dimension of $K$?
-1
votes
1answer
22 views

Finding current in a sphere while given a changing current density

im trying to calculate the current running through a sphere while given a current density $$J=Jcos(2\theta)e^{-t/r} \hat r $$ J is given in spherical coordinates. I know that: $$I=\int J\,da $$ But I ...
-1
votes
2answers
77 views

What is the lenght of the rope?

The $E$ string of a violin has a linear density of $0.5 g / m$ and is subjected to a $80\text{N}$ of tension, tuned for a frequency $u = 660 \text{Hz}$: What is the length of the rope? I know ...
-1
votes
1answer
79 views

Boundary conditions for the heat equation when solving a mass density gradient

I'm working with a mass density gradient with length $L$ and I'm trying to solve the heat equation in 1-D (mass diffusion equation, $\partial_t\rho(t,x)=D\Delta\rho(t,x)$), but I'm not sure which ...
-1
votes
1answer
33 views

How to calculate Acceleration

Assume you are moving 10 meters in 10 seconds northward. What is the acceleration?. Using this equation: $a = (v_f - v_o)/\Delta(t)$ and filling it in with this data: $v_f=1$ which comes from $10$ ...
-1
votes
2answers
43 views

Free fall question: Bill shoots his gun [closed]

Bill borrows his dad's gun and when he gets outside he fires it straight up into the air. If the bullet left the gun at 400 m/s: How long does it take the bullet to reach its highest point. I know ...
-1
votes
1answer
48 views

A block falling from a height on a block suspended by spring [closed]

The block suspended by the spring is hanging freely and its mass is M. The small block of mass m is dropped on the bigger block from height h. After the small block is dropped 》》》 I want help in ...
-1
votes
1answer
48 views

What are the the characteristics of a standing wave? [closed]

May someone explain #24 from this picture? B is apparently the correct answer. Can any of the other answers be correct here? Isn't D also correct?
-1
votes
1answer
152 views

Newton's Second Law Questions [closed]

The total mass is 2300kg (weight = 5072lbs). Find the size of the force due to wind and rolling friction when the van speed is 44.86mph (1mph= 0.447m/s). I am really at a loss of what to do here. ...
-1
votes
2answers
2k views

What is the fringe separation in Young's double slit experiment?

In the double slit experiment, a pattern of dark and bright bands appears on the screen. Is the fringe separation the distance between two bright bands? Question: In a double slit experiment ...
-1
votes
0answers
16 views

The magnitude of the resultant? [closed]

The two structural members, one of which is in tension and the other in compression, exert the indicated forces on joint O. Determine the magnitude R of the resultant R of the two forces and the angle ...
-1
votes
1answer
40 views

Finding charge (electromagnetism course) [duplicate]

I'm a maths undergrad taking a course on electromagnetism, I've drawn a diagram to represent this following question, but I'm having a bit of trouble approaching it: "Two tiny balls of mass m = 0:1 g ...
-1
votes
1answer
73 views

Oscillator, angular frequency equation

I found the highlighted equation on the Wikipedia on angular frequency, however it doesn't say how it was obtained, could someone please explain that? Also, it says that the spring is massless, if ...
-1
votes
1answer
66 views

What is the frictional force of this car? [closed]

The breaking acceleration for a car is $-12.2\frac{m}{s^2}$. The car has a mass of 925kg. I want to find the frictional force. Here is what I have so far: $$\Sigma\vec{F} = m\vec{a}$$ $$\Sigma\vec{F} ...
-1
votes
0answers
50 views

Mechanics Newtons third law [closed]

In the system suppose that the mass of the lower cylinder is $12 kg$. The system is held at rest in the position shown, with the tape taut and then released. Find the acceleration of a) the ...
-1
votes
0answers
60 views

Moments of inertia [closed]

A compound flywheel is to be constructed in the form of a circular disc with a radius of 0.25m, a thickness of 0.05m and a moment of inertia about its axis of 2Kgm2. the flywheel is to have a ...
-1
votes
2answers
52 views

A block in motion explodes [closed]

A 9.5 kg block (A) is traveling in the positive x-direction with a speed of 3.0 m/s. At some point, it explodes and breaks into two pieces. After the explosion, block C, which is 6.0 kg, moves off ...
-1
votes
1answer
68 views

friction between 2 bodies [closed]

There is a plank on which a block is kept. the block is given some velocity. Now if there is friction between block and plank it will act opposite to it's velocity for sure. but the plank is free to ...
-1
votes
1answer
62 views

Homework - Mechanics [closed]

Just started mechanics and I'm not sure what I'm doing wrong on a question. Car accelerates uniformly from a speed of $50\: \mathrm{kmh}^{-1}$ to a speed of $80\: \mathrm{kmh}^{-1}$ in $20$ ...
-1
votes
1answer
3k views

Rope tension between two objects [closed]

Let me explain the picture just to make sure. Object with mass 2 kg is being pulled with a force of F = 14.4 N. The whole system has an acceleration of a = 2.8 m/s^2. The friction coefficient ...
-1
votes
1answer
1k views

Finding the point of collision between two objects when acceleration is constant

$\newcommand{\accunit}{\mathrm{m}/\mathrm{s}^2}$ A coin is dropped 60.0m above the top of an elevator car. The coin is dropped just as the car begins to move upwards. The elevator first ...
-1
votes
1answer
274 views

Speed of a falling pencil [closed]

If you balance a pencil of length $d$ on its tip, and let it fall, how do you compute the final velocity of its other end just before it touches the ground? (Assume the pencil is a uniform one ...
-1
votes
1answer
28 views

Averaging energy density

Let we define energy density by, $$E= a^2 \cos2 t +b^2 \sin2 t+ c^2 \cos 3t$$ where, $E=$ total energy, $a,b,c =$constants, and $t$ is the time. I'm confused from someone's statement that ` There ...
-1
votes
3answers
206 views

Forces involved in a climbing jet aircraft

I have a problem with which I need help. The question is: A jet aircraft is climbing at an angle of 45° above the horizontal and is accelerating at 4.5m/s2. What is the total force that the cockpit ...
-1
votes
1answer
239 views

Acceleration, velocity and speed

It is given that acceleration is constant, so can we infer that average speed and velocity are the same?? Moreover, circular motion is out of the question, as the function of x(t) where ...
-1
votes
1answer
127 views

Neutron conversion to energy? [closed]

Numerical: If a neutron be entirely converted into energy how much energy would be produced. ($M_n = 1.6743\times 10^{-27}$kg.) Explain
-1
votes
3answers
207 views

What needs to be integrated to solve this problem?

An object is placed on a frictionless table with its one end attached to a cord which is connected to a pulley and the tension is maintained constant at 25 N. what is the change in kinetic energy ...
-1
votes
1answer
707 views

Potential due to a spherical surface charge

The potential at the surface of an insulating sphere (radius R) is given by $$V(R,\theta) = k \cos(3\theta)$$ where $k$ is a constant. Use separation of variables to find the potential inside the ...
-1
votes
1answer
152 views

electrical forces of two charges repelling each other

If I place two positive charges of different magnitudes on the x-axis (one at the origin, one at the some position x), as the two charges repel each other are the forces that they impart on each other ...
-1
votes
1answer
402 views

Find generating function $F_1$ for canonical trasformation

I'd like to know the steps to follow to find the generating function $F_1(q,Q)$ given a canonical transformation. For example, considering the transformation $$q=Q^{1/2}e^{-P}$$ $$p=Q^{1/2}e^P$$ ...
-1
votes
3answers
289 views

A simple logical problem regarding pressure and force

Suppose a 2 meter long pipe, with area of cross section is $1 m^2$. The pipe is vertically placed, with the bottom end closed. Inside the pipe, at the closed bottom end, there is $1 m^3$ of air, ...