# 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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### In the following problem, where did $v_{cm}$ come from? [closed]

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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### How can one conclude upward force is related to tension in this question?

In preparation for the SAT Physics Subject Test, I have been doing extra practice problems. This one states: A garment bag hangs from a clothesline. The tension in the clothesline is $10 \,\text{N}$ ...
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### Why don't hexapods gallop?

I haven't observed any terrestrial hexapods that gallop like agile tetrapods(cheetahs/horses). Instead, I've observed that all of them scuttle which constrains their maximum velocity. And after ...
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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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### Why don't we feel the subtle speed change of Earth's elliptical orbit?

Earth's orbit is a slight ellipse, so to conserve momentum its speed increases when it is closest to the Sun. If the speed changes there is an acceleration. If there is an acceleration there is a ...
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### Setting up equations for a vertical spring-mass system [closed]

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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### Moment of Inertia of a curved part of a graph [closed]

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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### Breaking Newton's 3rd Law?

I am having trouble explaining how the following experiment actually works, but it does.? Place a neodymium magnet on a piece of Styrofoam and a test tube of water next to it on the same piece of ...
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### Please tell me which of the Equation is wrong; the Angular momentum or the momentum? [closed]

(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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### Why does Goldstein's derivation of orbits from Newton's law not yield the orbit consisting of symmetric oscillation along a line thru center of Sun?

Why does Goldstein's derivation of Keplerian orbits from Newton's law of gravity not yield the orbit consisting of symmetric oscillation along a line passing thru the center of the Sun? The fact that ...
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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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### Kepler Orbits: Small Perturbations->Elliptical Orbits

A group of my physics classmates and I have been stuck on this problem. We have tried a few approaches. The problem is to show that a body following a circular orbit, when given a small radial ...
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### All about Frictions. (Help me) [closed]

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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### Why is the period of rotation the same for two stars orbiting the same centre?

In a binary star system, two stars $A$ and $B$ follow circular orbits, of radius $R$ and $r$ respectively, centred on their common centre of mass $O$. The mass of star $A$ is $M$, and that of star $B$ ...
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### Why centripetal force does not increase the value of tangential velocity? [on hold]

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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### 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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### Newton's law - satellite position (in 2D) for specific moment of time [closed]

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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### Dynamics of pendulum coupled to a gyroscope [closed]

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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### 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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### 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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### Will a tennis ball go further if i hit it with the side of the racket?

If i hit a tennis ball 'properly' on the stringing, does it go further than if i rotate the racket 90 degrees in my hand and hit the ball with the same force, but on the side of the frame? I'm ...
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### Why does galilean invariance imply that particles that start rest stay on the same line?

I'm reading Arnol'd for self study. I'm struggling with this question: "Show that any system of two particles will remain on the same line that connected them at the initial moment, if they started at ...
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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 [closed]

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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### Calculate torque to rotate and 84lb panel vertically from 0 - 90 degrees

I have a rectangular panel that weighs 84lb. Width (rotational axis) is about 60-inches. Height is about 32 inches. It will be lying flat and hinged (or connected to tubular motor) on the long edge. ...
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### How would you go about solving this difficult physics problem? [closed]

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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### Cause of SHM of liquid-column in V-tube

Suppose there is a v-shaped tube filled with water. The left limb is at $\theta_1$ & the right limb is at $\theta_2$ with the horizontal base. Initially, the level of water in both the columns are ...
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### Effect of position on a motorbike turning

While searching tips for driving a motorbike on wet roads safely, I heard some pilots saying to lean inside the slope makes the bike less tilted, so it's safer. I agree leaning make the bike less ...
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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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### Forces and acceleration on rotating objects?

Suppose you have an object undergoing uniform circular motion, with force vector pointing towards the center and another force vector tangential. Can it be said that the net force pointing in the ...
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### Find the mass of Europa, one of the Moons orbiting the Jupiter [closed]

Europa, one of the moons of Jupiter, was discovered by Galileo in $1610$. Europa has a circular orbit of radius $6.708\times 10^5$ km and period $3.551$ days. Find the mass of Jupiter. My attempt: ...
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### Relative wind velocity explanation - understanding Irodov problem 1.6

I am having trouble understanding the reasoning behind the solution in this Irodov General Physics problem. The problem is 1.6: 1.6. A ship moves along the equator to the east with velocity vo = ...
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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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### 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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### 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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### 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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### Why golf balls travel faster if they spin?

From the book I have been given to read I found that balls spin due to the centripetal force but i am confused about how exactly do the resultant force causes it to spin and move forward about the ...
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### Frictional force on an inclined plane with applied force = Mgsinx - Mgcos x?

I was reading Introduction to Classical Mechanics (Morin) recently and came across this example, which said that the friction force (marked $F_f$) is $Mg\sin\theta - Mg\cos\theta$. However, I can't ...
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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 can a satellite's speed decrease without its orbital angular momentum changing?

I have no idea what the answer is. I'm supposed to answer it within 3-4 sentences.
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### Position vs Time Function for a Falling Object Without Assumption of Constant Acceleration [duplicate]

If you have an asteroid for example and a planet, isolated from all other gravitational influence and initially at rest with respect to each other, how would you find a position vs time function for ...