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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1answer
13 views

Vibration of a string at a frquency other than the resonance frequency

We know that if we attach an oscillator/vibrator to a string with either the natural frequency or one of its harmonics, it exhibits resonance and a pure standing wave is produced. But here, i am ...
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Newtonian Mechanics: Acceleration of wedge

I have tried it considering the block and the wedge as a whole system and block. I have got the solution. However, I wanted to know whether we can use the block and wedge as separate systems. I have ...
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2answers
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A question about a efficiency

An electric lift has an efficiency of 72%. The machine lifts a box with the mass of 100kg to a height of one meter. How much energy is needed to lift the box? I have calculated the potential energy. $ ...
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1answer
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Find the thread tension where the body is hanging

Find the tension of the thread in the construction shown in the figure. The construction is in equilibrium. The mass of the hanging body is 6kg. the angle created between the wire and the wall is 20 ...
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1answer
24 views

How can you measure the coefficient of elasticity of a spring?

I have an experimental task of measuring the coefficient of elasticity of a spring. Can you give me an idea of what to do? Thank you!
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Ways in which the charging process for the capacitor can be sped up [closed]

State two ways in which the charging process for this capacitor could be sped up and what difference each method would make to the: (i) final charge stored. (ii) final energy stored. (iii) final ...
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Question is related to theory of relativity [closed]

A spaceship moving away from earth with velocity 0.6c fires a rockets whose velocity relative to the spaceship is 0.7c away from the earth. What will be the velocity of the rocket, as observed from ...
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2answers
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Find final velocity of an object on an inclined plane without knowing the mass

How do I find final velocity of an object on an inclined plane without knowing the mass of the object assuming that I have the degree, duration, and initial velocity? Without the mass, how can I solve ...
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26 views

Non-linear second-order equation with initial conditions [closed]

$$a(t)a''(t)+\alpha a'(t)-\beta a(t)a'(t)-\gamma a(t)^2+\xi=0$$ $$a(0)=0\qquad a'(0)=0\qquad a''(0)=0$$ All constant is positive and $a$ is just depending on time. This equation I have although is a ...
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Physics question about inner resistance [closed]

Two DC generators are connected in parallel and work on one load. The electric motor of the given generators is $110\mathrm{V}$, the internal resistance of the generators is $0.2\Omega$ and $0.25\...
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1answer
38 views

Finding the force exerted by a rotating hoop on a bead

I'm working through a problem and I don't understand how to approach it. (Not a duplicate of this - asking about a different thing) A square hoop with side length $l$ and vertices $PQRS$ (labelled ...
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2answers
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Potential problem

I have a question about the following circuit. I found it in a old textbook and I don't understand the solution. We know that the potential difference between points A and C is 5V, and that point A ...
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1answer
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Average and Instantaneous Acceleration

This example comes in my Physics book, but I don’t understand one part of the equation. The velocity of a particle moving along the $x$ axis varies according to the expression $Vx = 40 - 5t^2$, where $...
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Interesting inertia problem

Consider the following. A car is accelerating with acceleration $a$. A string is attached to the roof of the car and to the bottom of the string, an object of mass $m$ is attached. Given $\theta$, ...
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The question is about the forced damped oscillation?

A spring-mass system with m = 4kg and k = 35 N⁄m is forced to oscillate by an external harmonic force represented by (3.78N)$\sin\omega t$. Plot (schematically) the amplitude u0 versus ω ωn. Indicate ...
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1answer
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How do I work out air and water speed from a measured static force?

This is a real question - not homework - I am NOT a student... How fast is the water going through my 140mm diameter propeller when my boat is pulling 12kg against the tree it is tied to? Water is ...
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Kinetic energy of a single link with its mass concentrated at the center

What is the kinetic energy of a single link with its one end on the ground at an angle and rotating around that end, and its length is $l$ the center of mass is concentrated at its center of mass (see ...
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1answer
32 views

Galilean Binoculars Ray Diagram

I have to draw a ray diagram for Galilean binoculars. They have a convex lens for the objective lens and a concave for the eyepiece. Can someone draw it out or explain how to? Ray diagram has to ...
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1answer
50 views

Two boxes, identical other than mass and density, are pushed with a coefficient of kinetic friction $\mu$. Do they slow down at the same rate?

Do they slow down at the same rate? And stop simultaneously? I believe they do because $v_f = v_0 -\mu g t$ for both. But I'm not completely sure why that is. I've also seen another equation for the ...
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2answers
23 views

Understanding Snells Law in seismic waves

This is a homework question, Ill say it upfront. The Problem is given so: Earthquake causes a wave that meets a boundary between two rock substances. Incoming wave speed is 25 m/s and angle is 9 ...
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1answer
29 views

Error propagation with Log base 10

I have some data and some errors for the data. The task I have been given is to $\log_{10}$ both sets of data, and then deal with the errors to plot a graph. For natural logarithms, this is easier as (...
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0answers
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A thermopane window consists of two sheets of glass separated by a volume filled with either air (let us model air as N2(g) here) or vacuum

A thermopane window consists of two sheets of glass separated by a volume filled with either air (let us model air as N2(g) here) or vacuum. Assume that you are hired as a research scientist for ...
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1answer
64 views

Can these different Lagrangians lead to the same equation of motions? [duplicate]

A particle of mass $m$ moves in one-dimension with position $x$ and potential $V(x)$, described by the Lagrangian $$ L = \frac{1}{12}m^2 \dot{x}^4 + m \dot{x}^2 V - V^2 $$ Show that the resulting ...
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Vector Calculus [closed]

The vector field: $$A = \boldsymbol{\mathrm{Y}}ax−\boldsymbol{\mathrm{X}}ay+\boldsymbol{\mathrm{Z}}az$$ is given in rectangular coordinates. Find the surface where $|A|$ is a constant.
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3answers
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Where must one use $x=A \cos \omega t$ and $x=A \sin \omega t$? [duplicate]

Consider the following example: A particle oscillates with simple harmonic motion in a straight line. In the first $t$ seconds, it travels a distance $a$. In the next $t$ seconds, it travels an ...
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Determine the angular velocity [closed]

I don’t know how to start,someone who can give me some tips ? I know that we can use energy conservation $K_{0}+U_{0}=K+U$. There $K_{0}=0$ because it starts from rest this how far I got: A wire roll ...
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Diffraction grating with a lense and a CCD sensor

I have a physics problem which I can't wrap my head around. It involves a diffraction grating with 500 lines/mm in a spectrometer used to analyze parallel visible light (390-770nm wave length). After ...
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0answers
21 views

Electric field at the centre of a charged spherical shell [closed]

What will be electrical field at center of a spherical conducting shell which has charge Q distributed uniformly on it? What will happen to electric field at center if we bring another charge Q' near ...
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1answer
57 views

Collision of a ball with wedge

Question:- A ball of mass $m$ with velocity $u_{0}$ collides perpendicularly with smooth wedge of mass $M$. Taking coefficient of restitution as $e$. Find velocity gained by wedge after collision. ...
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1answer
45 views

Application of the principle of conservation of angular momentum and the principle of conservation of energy

I came across this question and was left confused. A satellite is launched in a direction parallel to the surface of the earth with a velocity of $36900 \; \mathrm{\frac{km}{hr}}$ from an altitude of $...
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46 views

Variation of $x$ with respect to time?

A block of mass $m$ is gently attached to the spring and released at time $t=0$ when the spring has its free length as shown in the figure. During the subsequent motion of the block, find the ...
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1answer
17 views

A force is applied at different heights on a sphere kept on horizontal smooth surface. What axis it would rotate about in each case and how?

The acceleration of the centre of mass will be F/m, no matter what the height of point of application of force. How would the rotation of the sphere be, what is the axis of rotation? Also, if it does ...
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Find the electric field a distance z above the centre of a flat circular disk of radius R that carries a uniform surface charge σ

Find the electric field a distance z above the centre of a flat circular disk of radius R that carries a uniform surface charge σ. My solution is: The electric field due to each ring is correct as ...
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2answers
82 views

Separation of variables for a function of 3 variables $V(x, y, z)$

I'm trying to find the solutions for $V(x,y,z)$ by separation of variables. Is it correct to say: $$\frac{1}{X}\frac{d^2x}{dx^2} + \frac{1}{Y}\frac{d^2y}{dy^2} + \frac{1}{Z}\frac{d^2z}{dz^2} = 0$$ ...
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2answers
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How do you incorporate friction into kinematics?

A small disc of mass $m$ is pushed to $v_0$ on a surface with kinetic coefficient of $\mu$. Is $v_f = v_0 -{\mu mg} \text{ t} $ ? (Just based on the idea that increasing $\mu$ , $m$ or $g$ would ...
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2answers
44 views

Two bubbles attract or repel?

I have this weird thought that bothers me, but unfortunately, I know little physics and I thought I can get help to mentally settle it. Here we go: Let's say you have infinite sand or at least a vast ...
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2answers
60 views

Resolution of force sum [closed]

I was able to find the resultant of the forces in the question below by resolving them. I am facing a dilemma problem in whether we have to actually find the resultant force or the moment of forces at ...
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1answer
56 views

Why does Gauss' Law derive a different electric field from the integration method?

I was working on a very simple E&M problem and took two different approaches to it but got different answers - I'd be grateful if someone could spot the error in my logic! A non-conducting solid ...
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39 views

Computational Physics by Mark Newman (z-lib.org), [closed]

A spaceship travels from Earth in a straight line at relativistic speed $v$ to another planet $x$ light years away. Write a program to ask the user for the value of $x$ and the speed $v$ as a fraction ...
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0answers
28 views

What is the angular momentum of a double pendulum?

Is there a specific formula to calculate the angular momentum of a double pendulum?
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1answer
46 views

A car travelling along a straight road is leaking oil. What is the acceleration of the car? [closed]

A car travelling along a straight road is leaking oil. Drops of oil fall on to the road leaving the pattern shown in the diagram. The time between each successive drop is 2 seconds. What is the ...
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0answers
24 views

A light, conducting, metal sphere charged negatively is suspended on an insulating nylon thread. What is a possible motion of the sphere? [closed]

A light, conducting, metal sphere charged negatively is suspended on an insulating nylon thread. A positively charged plate is bought close to the sphere, as shown in the diagram. What is a possible ...
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0answers
21 views

Finding the Magnitude of $F_3$ Given that Vector Components are Equal along the Axes

I have initial solution in this problem. The goal is to find the magnitude and direction of $F_3$. Since Forces are resolved, then $F_1$ = $F_1, v$ + $F_1, u$ $F_2$ = $F_2, v$ + $F_2, w$ $F_3$ = $...
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24 views

Energetic radiation belt particles bounce motion period

How to show that energetic radiation belt particles experience a force along the direction of the geomagnetic field due to gradients in the ambient field strength? Also for particles ...
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0answers
26 views

Need help on a question from Feynman Lecture exercises [closed]

I am working through the feynman lecture exercises and am stuck on question 1.10. The question is stated below The intensity of a collimated, parallel beam of potassium atoms is reduced $3\%$ by a ...
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0answers
28 views

Using convolution theorem to show that f*g = f(t-t_0) when g is a dirac delta function [closed]

I'm still learning fourier and one of the questions I've been asked is related to convolution theorem. I am already struggling conceptually with this idea. We are told to consider a top-hat function g(...
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3answers
45 views

Rate of Heat Flow

I was given a problem that asks me for the heat transfer power, also specifying that the heat transfer power is directly proportional to the difference in temperature. Does it refer to the rate of ...
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1answer
93 views

Finding charge density $\rho(r)$ from long wire of charge

Given a long wire of charge, with uniform charge density $\lambda$ Coulombs per m. For a charge density $\rho(r, \theta, z)$ which depends only upon $r$ and varies linearly from the center and is $0$ ...
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0answers
17 views

Work in increase charge in a isolated conducting sphere

The potential of an isolated conducting sphere of radius R is given as a function of the charge $q$ on the sphere by the equation $V = kq/R$. If the sphere is initially uncharged, the work $W$ ...

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