# Questions tagged [homework-and-exercises]

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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### How to determine the direction of acceleration for block A and man? [closed]

My confusion is how to determine the direction of acceleration of block and man. I know that in the same direction. acceleration of Man wrt rope/block will be Acceleration of Man minus Acceleration ...
0answers
63 views

### Conserved quantities of a simple Lagrangian

Suppose the following Lagrangian with 2 degrees of freedom: $$L = \frac{3}{2}\dot{q}^2_{1} \ + \frac{3}{2}\dot{q}^2_{2} \ + \dot{q}_{1}\dot{q}_{2}$$ My aim is to find all the conserved quantities of ...
1answer
54 views

### Show for $r \in \mathbb R$, $e^{(a_1 ^\dagger a_2^\dagger - a_1a_2)r}|0,0 \rangle = \frac{1}{\cosh r} \sum_{j=0}^\infty (\tanh r)^j |j,j \rangle$

Let $a_1, a_2$ be annihilation operators for the first and second component in the product state $|m,n \rangle$ using Fock basis. Following "Quantum continuous variables, A primer of Theoretical ...
0answers
30 views

### Determining whether I hit the bed when jumping from a cliff [closed]

For simplicity, assume a perfectly spherical object with uniform density falling from some height to a lake. How can I determine whether I hit the bed of the lake? Maybe this has something to do with ...
0answers
28 views

### Relation between current (not at saturation) and voltage in photoelectric effect

This is the question I got for an assignment. How do I determine stopping potential from this data? I can see that the relation between $V$ and $I$ seems to be linear, so can I just use the equation ...
0answers
31 views

### The exact location of normal force and friction vectors [on hold]

I am struggling with a following question: "A cylinder of radius $r$ and height $h$ is standing on an inclined plane pitched at an angle $\theta$ to the ground. Given the coefficient of friction $\mu$ ...
0answers
35 views

### Please check my problem about SI prefixes [closed]

2.2 A single logic gate in a prototype integrated circuit is found to be capable of switching from the “on” state to the “off” state in 12 ps. This corresponds to: (a) 1.2 ns; (b) 120 ns; (c) 1200 ns; ...
1answer
33 views

### Change of variable in 4D space-time

I was reading Sidney Coleman's article "Fate of the false vacuum: Samiclassical theory" and i stumbled upon a change of variables that i can't seem to prove. The problem is this: trying to solve the ...
0answers
12 views

### Why the sum of deformations in given figure is zero?

When a vertical block is kept between two fixed support and when the bottom support is removed, it has the possibility of facing a deformation downwards which was impeded by the upward reaction force ...
0answers
23 views

### Toilet Paper roll [closed]

Why we don't replace R in formula （RT=（1/2)m(R2+r2)(a/R)) into (R,outer diameter +r,inner diameter)? Does the inner roll also rotate?
1answer
42 views

### Inverted pendulum, EOM

Consider the inverted pendulum shown below: where $F$ is an external force, $B$ is the CoM of the rod, $A$ is the position of the joint where the rod attaches to the car. Angles increase in the ...
0answers
24 views

### external pressure vs internal volume plot of 1. expanding and 2. contracting cylinder-piston-gas system that obeys Boyle's law [closed]

A gas which follows Boyle's law, is enclosed inside a standard piston-cylinder system having volume V and pressure P. If an external pressure is applied to that massless piston to 1. slowly compress ...
0answers
28 views

### How to solve for stable/unstable equilibrium in this question [closed]

A solid cube of side b is at rest on curved surface of a cylinder(horizontal axis) of radius R. Assume no slipping. We have to derive condition for stable equilibrium. My approach: Slightly we can ...
2answers
45 views

### Can someone explain these circled points…?

Why is direction of friction in the direction of motion and here it is the platform that moves....the movement is not caused by friction so how is friction doing work? In the second one there is no ...
1answer
80 views

### How can i obtain the correction to the eigenvalues as a result of adding the gravitational potential to the hydrogenlike atom?

In treating the hydrogen-like atoms, we normally neglect the gravitational potential for the system. I am able to justify the above statement by comparing the gravitational potential to the ...
0answers
30 views

### What will be the equation of the path of spider? [closed]

A cobweb thread of negligible relaxed length is traced between points A and B on two opposite walls as shown in the figure. In this state the thread makes an angle $\theta$ with the horizontal and ...
0answers
12 views

### Factors effecting amplitude of damped spring

Let say we have a spring under simple harmonic motion. What are the independent variables that effect the time taken to reach half the initial amplitude during damping? I am guessing a few would be ...
0answers
39 views

### What's the shortest “safe” distance from a neutron star merger?

Take GW170817 for example, the first neutron star collision picked up by LIGO. Given how much data we got from that event, can anyone figure out what the "blast radius" is, and how far away from the ...
0answers
15 views

### Analysing a lift moving up with acceleration from the inertial frame of the ground

A frictionless inclined plane,making angle $θ$ with the horizontal, of length $L$ (inclined plane is a right-angled triangle, $L$ is length of hypotenuse) is kept in a lift which is moving up with ...
0answers
34 views

### A tug of war with different forces at each end of the rope [closed]

If a man pulls a rope with a force of 150N towards him and the other end of the rope is pulled by a small girl with a force of 50N towards her. Assuming rope to be massless. Find tension in the string....
0answers
40 views

### How am I supposed to get this answer? [closed]

This question is from the Oxford Physics book, and I didn't understand how to get the answer. I'm assuming that the equation that I'm supposed to use E=mc^2 to solve the equation.
1answer
111 views

0answers
35 views

### Young's double-slit in Sound waves [closed]

I am going my physics extended essay and I am stuck in explaining my hypothesis. So I am doing an experiment where I have 2 sound sources emitting specific frequencies and I am trying to find fringe (...
1answer
40 views

### What's wrong in my approach towards solving this problem?

This is the problem that I have to solve: The figure shows a block $A$ of mass $6m$ having a smooth semicircular grove of radius $a$ placed on a smooth horizontal surface. A block $B$ of mass $m$ ...
1answer
63 views

### An Evil Vector Problem! [closed]

A person is walking on straight road starting with a velocity $v$, the direction of of air ,observed by him makes an angle $\alpha$ with his is direction of motion. Now during the race, he finds ...
1answer
103 views

### Doubt in quantum mechanics [closed]

My lecturer said that when a oscillating body loses energy in the form of radiation the natural frequency of oscillation is equal to the frequency of the emitted radiation. Can someone explain why?
1answer
73 views

### How can I calculate the equivalent resistance of this circuit with resistors in parallel with wires? [closed]

Problem: Calculate the equivalent resistance, $R_\text{eq} ,$ of this circuit: $\hspace{50px}$. My solution attempt Тhe $12 \, \Omega$ resistor and the $6\, \Omega$ resistor are in parallel, ...
0answers
52 views

### How would I calculate the gravity on the surface of a large rectangular solid? [closed]

This story on Reddit involves a 1 km by 1 km by 1.79 lightyear block of lead in deep space, and I was wondering if it was at all feasible (though that question is probably out of scope). To ask a more ...
1answer
83 views

### Energy eigenvalue with Potential $-e^2/ x$

If I have potential which are very well-known like, square barrier, or square well, or step potential, What I do is to set the boundary conditions in Schrödinger's equations. Sometime, the ground ...