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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Fallacious derivation of the rocket equation

Consider a rocket in free space of initial mass (including fuel) of $m_0$ using up/ejecting fuel at a constant rate $r$ (mass per time). That means that at time $t$ the rocket has mass $m=m_0-rt$. The ...
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7answers
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Why is force a vector? (The Feynman Lectures)

A vector is a quantity that transforms just the way the coordinates transform under rotation (while a scalar remains invariant under rotation). In FLP, he says suppose $F$ is a vector and probably ...
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1answer
115 views

Effect of general relativity on Newton's second law

Let's say I have some object, like a long pole, that is 30 km long with non-zero mass $m$. One end is resting on the Earth's surface and it is sticking straight up, perpendicular to the surface. ...
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1answer
109 views

Derivations of Newton's laws?

I feel convinced that the mathematics behind newtons laws can be derived from Noether's symmetry theorems. The fact that displacement s can be described by a cartesian coordinate system with a ...
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1answer
84 views

Cylinder on an accelerated rough plane [duplicate]

The following figure shows a cylinder resting on a rough horizontal rug that is pulled out from under it with acceleration $a$ perpendicular to the axis of the cylinder. What is the motion of the ...
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2answers
56 views

How can amplitudes be treated as vectors in Simple Harmonic motion?

The amplitudes of 2 SHM are scalors. When we combine the two SHM eq.(lying along the same line), the resultant expression becomes of amplitudes treated as vectors and the phase angle between them as ...
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1answer
61 views

Moment of Inertia of Square Lamina [closed]

I know how to compute this using an integral. However, I was told that I could derive this as well by placing 4 squares together of moment of inertia $$I=kmr^2$$ and derive it again but I'm not sure ...
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1answer
36 views

Solving an acrobat problem in 3 methods

A circus acrobat of mass $M$ leaps straight up with initial velocity $v_{0}$ from a trampoline. As he rises up, he takes a trained monkey of mass $m$ off a perch at a height $h$ above the trampoline. ...
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2answers
93 views

What formula do I use to calculate the force of impact of a falling object?

I am trying to calculate the force of impact of a falling object. I did my egg drop project. I dropped the egg from 10m with a mass of 126kg and with the velocity of 14.1 m/s. Which formula should I ...
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1answer
79 views

How can the work done by friction be positive? [closed]

I have this energy related problem that i cannot understand in this problem, I am required to find the velocity of the 4.8kg mass when it hits the ground. I easily solved this problem using newton's ...
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3answers
142 views

Resolving horizontal and vertical components on an inclined plane

Here is a very simple mechanics question related to inclined planes: We assume that the body is at equilibrium or at constant speed. To work out the force 'R', I resolve the 100N force due to ...
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2answers
91 views

Newton's third law & punching walls [closed]

N-law 3: if you punched a wall as hard and as you could, would it possible to retract your hand before the reaction from the wall could affect your hand less than if you wouldn't retract at all? ...
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1answer
57 views

A heavy chain with upper end falling with constant velocity

The most basic form of my question is: "Can the normal force from the ground be enough to let a chain's upper end fall at constant velocity?" I suspect the answer is no, but to elaborate, here is the ...
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3answers
98 views

Frictional Force of a Rolling Object

I'm not sure that I understand this problem: A spool of wire of mass 4.7kg and radius 0.99m is unwound under a constant wire tension 10N. Assume the spool is a uniform solid cylinder that rolls ...
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2answers
68 views

What does well defined parity mean

I'm reading a textbook (Physics of Quantum Mechanics by Binney) and it says that the ground state ket $\left\lvert 1 0 0 \right \rangle$ of the hydrogen atom has well defined (even) parity. What does ...
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1answer
166 views

Would a non-rotating Earth collapse on the Sun?

If the earth stopped rotating on its axis, would this influence its revolution motion? In particular, could it collapse on the sun? I ask this because on the one hand I thought the two degrees of ...
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2answers
64 views

Conservation of momentum for moving inclined plane

I'm confused about the conservation of momentum in problems involving inclined planes that moves. Consider an inclined plane free to move on the floor and a body on the edge, there is no friction at ...
2
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2answers
78 views

Condition for looping the loop

Consider a ball tied to a string and it is imparted a velocity we have studied that condition for looping the loop is that tension at the uppermost point must be zero, but why is this condition ...
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0answers
71 views

Moments of inertia of composite area - xaxis [closed]

struggling with this question. Got the a) ( y¯ = 3.79 in )but can't seem to get b) a) Locate the centroid y¯ of the composite area. b) Determine the moment of intertia of this area about the ...
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1answer
47 views

Reason behind Inertia

Has any physicist work on the reason behind Inertia? Why do we have inertia only during acceleration? No inertia during constant velocity.
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46 views

Why does work in the Work Energy Therom equal the Sum of the integral F*dr?

I am studying the work energy therom and I understand that 1/2(mv^2)=Wnet, however, I saw this picture below online. I understand the summation of the force times the change in distance. However, ...
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1answer
44 views

Will the Earth ever show synchronous rotation? Why and when?

In this answer to the question "why does the moon have the same rotation and revolution periods?", we read: The mass and speed of rotation of the Earth influence the moon in that some of its ...
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2answers
99 views

Elastic potential energy and equilibrium position when mass changes in vertical mass-spring system

I'm a bit stuck with this situation: Suppose that an object $A$ with mass M=8 kg at 10 mt above the floor falls from rest tied to an 2 mt elastic rope, which does not exert any force since $A$ falls 2 ...
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3answers
40 views

Role of forces in this collision?

Consider two identical objects of equal mass collide with eachother with equal opposing accelerations. Wouldn't the forces of the objects cancel each other resulting in the objects both comming to a ...
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2answers
156 views

Concept of mass

In classical mechanics, there seems to be a need to distinguish between inertial and gravitational mass. Some texts show how the concept of mass may be defined with some mathematical rigor. There is ...
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1answer
42 views

Conservation of energy in the “ideal physics world”

Let us assume we are in the textbook ideal physics world, without any friction. Now, if I place a ball at the top of a parabola U and let it go under gravity, the ball should roll up and down forever ...
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3answers
66 views

Net force for circular motion

So today my physics teacher was telling us that the net force when discussing circular motion was actually the centripetal force. He didn't go further and I would like to know if there's any proof to ...
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1answer
45 views

Why are my answers wrong for braking distances? [closed]

I have been working on a presentation to find the braking distances at the velocities of cars obeying speed limits for a range of common speed limits. I'm working with the equation $$d= \frac{v^2}{...
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1answer
245 views

Is there a charge density in quantum mechanics?

Is it meaningful in quantum mechanics to speak of charge distribution? Some people say if you sovle the Schroedinger Equation for the hydrogen atom, the eigenfunctions represent a type of charge ...
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2answers
103 views

Work energy theorem explanation

So there is this problem in my head, it may seem very simple, but I need an answer. The problem is, we have some object, and we apply a force by our hands with a constant speed from a position (1) to ...
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2answers
101 views

How to find speed of rotation of gears from kinetic energy of falling body?

A pulley is fitted to the first driven shaft of compund gear train. Last driven shaft of gear train(gear 8) is fitted to the 12V DC generator (6W).Now to the rope extension at the one end of the ...
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2answers
163 views

Does the Inertia of a Cue Ball Affect its Reflection Angle off a Resting Billiard Ball?

Consider the following Diagram in which a Cue Ball (A) of mass M is shot twice at another pool ball with identical mass M. When the force with which the cue ball (A) is hit (v1) is increased (v2) ...
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3answers
63 views

An object is accelerating on a rough surface with frictional force of 10N. Is the friction doing any work on the object?

This question might look stupid to some but I am in great confusion. An object, say a box, is moving on a surface with some velocity v and is accelerating. It means that the force applied by the box ...
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4answers
108 views

When is tension positive?

A 5kg mass is hanging from the roof of an elevator accelerating downward at a speed of 1.65 m/s^2 what is the tension of the string (ignore friction, string mass, and air resistance) ? I used this ...
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0answers
39 views

Can one use Newton's second law to describe a system of different internal accelerations?

example: a mass is connected by a massless cord to another mass that is on an inclined plane through a pulley of no mass and friction. I assumed the two masses to be a system because of the cord in ...
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2answers
65 views

Planets potential [duplicate]

I'm a physic student of Italy. I'm moving my first steps in this beautiful world, and as every new entry, my simple and stupid questions are sometimes not so simply resolved. I'm trying to know the ...
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1answer
44 views

Question about 3d collision of 2 particles [duplicate]

I'm wondering about how to calculate the resultant velocity vectors of an elastic collision of two particles of same mass, in 3d. I've seen a post on the subject in which you answered, but I didn't ...
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0answers
40 views

Stability of plants and buildings: the role of the xylem

Dicotyledon plants show a stem structure with many xylem tubes, hollow but with lignified (woody) walls. These are arranged as in the figure below, in a circle. Their roots, on the other hand, have ...
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2answers
69 views

One dimensional motion - Why does a ball fall back in my hands when I throw it up in a moving bus? [duplicate]

Suppose you are moving in a bus and you throw a ball upwards. Why does it always land in your hand and does not fall behind you? The bus is moving with a uniform velocity in a straight direction. Now ...
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1answer
49 views

Interpreting force components in statics problems involving inclined planes or similar

I'm having troubles to understand how to interpret the components of forces on inclined plane in quite complicated situations. I will make an example of one of the cases where I get confused. ...
3
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2answers
76 views

If displacement is 0, why isn't the work performed on an object 0?

Work is force x distance/displacement. The exact definition is something I'm a little confused about since my professor said it could either be distance or displacement. So going with that, if the ...
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0answers
40 views

Semi-major axis , specific mechanical energy, its period and velocity at Apogee and Perigee and what the difference is [closed]

Hi im needing some help with two questions could you please show the formula and the way its solved?Thanks PS:Could you also explain what the difference of velocity and apogee and perigee? 1.)A ...
2
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2answers
119 views

In what direction should you throw a 1Kg uniform sphere in order to put it into lower earth orbit? [closed]

If you are standing on earth's surface, in what direction (and at what speed) should you throw a 1Kg uniform sphere of radius 0.1 meters in order to put it into lower earth orbit? Assume that there ...
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0answers
106 views

Three-log problem [closed]

Three uniform round rigid cylindrical logs of the same size and weight are placed on a horizontal plane. The two at the bottom are touching each other, the third one is placed on the top as shown in ...
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0answers
17 views

Cylinder placed in wedge which inturn is on wedge [closed]

A cylinder of mass m rests in a supporting block as shown. if beta = 60 degree and theta = 30 degree, calculate the maximum acceleration a which the block may be given up the incline so that the ...
0
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1answer
53 views

Collision of moving large mass and small stationary mass?

Hypothetically if a mass, roughly the size of earth, was accelerating at 100m/s and came in contact with a 1kg stationary mass, due to newtons 3rd law wouldn't the small mass accelerate and the large ...
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1answer
80 views

3D beam deflection

How can you get formula for 3-dimensional beam deflection at the free end of horizontal cantilever due to the cantilever's own gravitational load? I assumed E= 160GPa, $\nu=0$, $\rho=2330kg/m^3$, ...
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3answers
77 views

Calculate acceleration based on differential pressures

In my example, water is in a tube and is being accelerated by a compressed air. I already know that $P = \frac{F}{A}$ so if you know the pressure and you know the surface area its acting on, you can ...
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0answers
25 views

How to describe the forces on a weblock?

I am trying to figure out the forces on a weblock when two strands of webbing are wound around it. I have made an attempt but would like to know if I am on the right track or not. A short background, ...