# Tagged Questions

Newtonian mechanics covers the discussion of the movement of classical bodies under the influence of forces by making use of Newton’s three laws. For more general discussion of energy, momentum conservation etc., use classical-mechanics, for Newton’s description of gravity, use newtonian-gravity.

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### Polar Coordinates for mass spring damper [on hold]

I have a follow up question to this question as I need to convert a simple mass spring damper to polar coordinates. The question should be easy and I would have assumed there are scores of textbooks ...
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### Work done by internal forces of a rigid body

I am reading Goldstein's Classical Mechanics book, and I came across that: In a rigid body the internal forces do no work Is this statement based on the assumption that the internal forces are ...
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### How do rockets fly? [duplicate]

Is it that when a rocket loses its mass due to the escaping gases that results in its acceleration due to the same force acting upwards? If so, how is Newton's Third Law associated with it?
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### Stuck with 2D kinetics problem [on hold]

I've been trying to solve this exercise for the last four hours and I'm totally stuck. The problems goes like this: Given the mechanism in the image, located in the vertical plane, the OB cord ...
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### Forces on body above body moving at constant velocity [on hold]

Let's say the system is moving at constant velocity. What are the forces applied on B? Is there a static friction force? I find it hard to imagine what is happening to object B. $\Sigma F$ is $0$ on A ...
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### understanding kinetic friction [on hold]

I have a pen on my table. I apply force horizontally to my pen. The force I apply is stronger then the maximum static friction so it moves. I move the pen at constant velocity. Now if we look ...
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### How do gravitational sling shots work? [duplicate]

How can an object move faster after leaving the gravity of a planet, should a gain in potential energy by moving away from the planet lead to a loss of kinetic energy? Or am I missing something ...
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### Riemann Invariants

I understand that the Riemann Invariants for an expansion wave (isentropic) are constant along the particular characteristic line i.e.: $u + \frac{2c}{\gamma-1} = const$ along $dx/dt=u+a$ (1) ...
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### In the following problem, where did $v_{cm}$ come from? [on hold]

In the following problem, where did come from? I don't recall any formula that this equation could be derived from...?
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### Setting up equations for a vertical spring-mass system [on hold]

I am preparing for an exam in classical mechanics and today I have encountered a slight problem when solving a more complex spring-mass system. Consider the following setup: Then the system of ...
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### Please tell me which of the Equation is wrong; the Angular momentum or the momentum? [on hold]

(Sorry, it's not 2M. It's m+M) Two rigid body is fastened at a stick. A bullet collides into the first body and become one, and the stick rotates. When the bullet collides, there is no outer torque ...
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### Conservation of enegry in case of Exploding Projectile [on hold]

Consider the following problem : A projectile of mass M explodes, while in flight, into three fragments. One fragment of mass $m_1 =\frac12 M$ travels in the original direction of the projectile. ...
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### All about Frictions. (Help me) [on hold]

A 20-kg body is on a plane inclined at 60° from the horizontal. The coefficient of friction is 0.22. What force at 30° with the plane will cause the body to move upward at a uniform speed? 2.A block ...
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### Friction and movement in a system with body above moving body in newtonian mechanics [on hold]

I have a problem in analyzing movement with friction involved. I do not know how to correctly analyze systems as such and what is the correct view. I have tried to answer the several question below. ...
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### Moment of Inertia of a curved part of a graph [on hold]

How to find the moment of inertia of a curve about a given axis. For example : How can we find the MI of the curved part of :$$\sin x\$$ EDIT: Assume the range from $$[0 ,2\pi ]$$ and the axis to ...
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### Foucault pendulum, where did I go wrong?

I wanted to approximate the number $N$ of periodes needed, such that the foucault pendelum turns one time. Though my result is off by the factor 2 of the results I found. What I did: I assume the ...
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### Dynamics of pendulum coupled to a gyroscope [on hold]

We know the dynamics of a pendulum and we know the dynamics of a gyroscope. I put together the following I diagram below. The interesting thing as that the system has a beat frequency where the ...
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### Can one rise through a free-falling rope?

I am a little confused about this question. I cannot imagine that it is possible to rise through a rope (assuming inextensible) that isn't fixed in its upper end. But when I solve this problem, I see ...
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### Conservation of Energy with Rotation Caused by Friction

A book that I am using to study poses the following problem: Suppose you wish to use a spring with a force constant $k$ to launch a spherical ball or radius $r$ and mass $m$ up a ramp of inclination ...
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### Newton's law - satellite position (in 2D) for specific moment of time [on hold]

I’m trying designate function that calculate satellite position (2 dimensional) for specific moment of time for better understanding Newton's law of gravity. To verify my calculations I created second ...
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### How to calculate the elapsed time to reach x? [duplicate]

Can some one provide a guideline about how to solve this problem?
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### How to calculate the time for reaching 1/2 of the height for an object [on hold]

I need to calculate the time for reaching the red object to the 1/2 of it's height. Can somebody provide me some guidelines?
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### How would you go about solving this difficult physics problem? [on hold]

I was able to calculate an angular frequency of 85.4357 rad/s for this mass. However, I am confused as to what to do next. Any ideas?
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### How do I calculate a upward-pulling force on a swinging pendulum?

I'm trying to implement a simple pendulum using a 2d physics system that can model rigid bodies with gravity. The problem is that I don't know how to calculate the upward-pulling force of the rope, as ...
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### Validity of Point Mass Approximation in Newton's Laws of Motion

Chapter 2 of Kleppner & Kolenkow's An Introduction to Mechanics reads as follows - Newton's Laws describe the behavior of point masses. In the case where the size of the body is small ...
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### Why centripetal force does not increase the value of tangential velocity?

I found in a text book that the value does not change because the centripetal force is perpendicular to the tangential velocity. But I am confused, because a vector can have a component, which is ...
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### Why does the amplitude of the pulse never return to its original value when the number of waves used to construct it tends to infinity?

I was reading Constructing a pulse of Modulations, Pulses, and Wave Packets from Waves by Frank S. Crawford Jr. ; here, in the following concerned excerpt, the author is describing of constructing a ...
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### Is it possible to throw a stick without giving it a rotational motion?

When walking with our dog I always throw wooden sticks for her. Then one time I wondered if I could throw the stick (normaly, so not like a spear) without imparting on it a rotational motion around ...
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### Pressure in deodorant can

Pressure in a deodorant can is greater than the surrounding pressure but still the can is in equilibrium with the surrounding . Why does this happen. If we apply $F = PA$ then $P_{in}A= P_{atm}A$ and ...
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### Does a counterweight eliminate recoil/counter-torque?

A long, long time ago, I remember reading some scifi book that involved catapults whose throwing arm had a counterweight at the other end, such that the arm was balanced. The counterweight was not ...
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### I know that free fall in vacuum is independent of mass. But what happens in air?

Pardon me if this sound somewhat trivial to some of the highly qualified users here. So I know two objects will fall at the same rate if they are in absolute vacuum, so what I'm assuming is that the ...
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### How fast was the car going that hit me? [closed]

Can someone help? We were in a car wreck and I'm trying to figure out how fast the lady who hit us was going. She told the police 50 mph, but I don't believe it. We were going through an intersection ...
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### Elastic Surface Waves

In the book by Landau and Lifshitz on elasticity they introduce the concept of surface waves. Does anyone know how to write down a Lagrangian including source terms for surface waves? In this case, a ...
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### Proving that force satisfies the laws of vector addition [duplicate]

A vector quantity has both magnitude and direction. So, for any physical quantity to be a vector, it should have a direction and a magnitude. Though this is a necessary condition for any quantity to ...
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### How high do you need to be so as to not rotate along with Earth?

So, I saw this meme about some minister commenting that the Earth doesn't rotate, for if it did then planes only need to be in the air and the destination city would come to it. I know this is absurd ...
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### A question on uniform circular motion and minimum tangential velocity

I've had a bit of a crisis in my understanding of circular motion and I'm hoping to clear it up here. Would it be correct to say that the condition for a particle to be in uniform circular motion is ...
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### Can an object take off from A, do not move (in the air) but land at a different place? [closed]

Can an object take off at a point A on the surface of the Earth and then land after some time only to land at a different place where it initially took off (because in the mean time the Earth has ...
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### A ball rolling at the bottom of a spherical bowl [duplicate]

This ball oscillates at the bottom of the spherical bowl which has sufficient friction that it doesn't slip throughout the motion and rolls without slipping. At the extreme points of its motion (as ...
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### Can we know the tension of the string that is connected to a pully?

If the pulley have mass, I learned that T1 and T2 isn't same. then what about the circled part of the string? can we calculate the tension with given T1 and T2?
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### Pulling and pushing two objects through a rigid member in between the objects [closed]

Problem statement: I have two objects of mass $m$ placed at some distance and connected each other in-between with a rigid member which can take compression or tension. Through a point on rigid member ...
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### Can we move our arm in a perfectly friction-less world?

Current question is related to some of answers given to this question. The answer given by hapa that has been confirmed by some other users in their answers, is as below: If there is no friction, ...
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### Where did 2mv come from in the solution to the question below?

I know that this is an inelastic collission, which is why the two objects have the same final velocity. However, I don't understand why they equated the V1(M+m) to 2mv. Where did they get 2mv from?