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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252 views

Confusion about gravity

I understand the “rubber sheet” model of Relativistic gravity is just an illustration, and beyond the initial issues of mixing three-dimensional objects with a two-dimensional representation of 3D ...
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1answer
92 views

Calculating mass of an orbiting body with force and acceleration

I'm new to physics, and it's a lot to take in- but there is a problem that I really can't seem to wrap my head around- finding the mass of an orbiting body, like an asteroid. I've looked around a lot ...
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2answers
453 views

Why is kinetic friction less than static friction? [duplicate]

Ex: A wooden block is lying on a table. I am told that because the block is still, the microscopic surface irregularities form more complicated interlocking structures. Is it because the force of the ...
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2answers
76 views

How fast would someone travel by jumping out of a spaceship into space [closed]

If someone without any propulsion jumped from a stationary ship in space, how fast would they travel?
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3answers
255 views

Why does the work-energy theorem need to include internal forces?

Can anyone kindly explain me why work energy theorem must also include internal forces? The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
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1answer
64 views

Work done should be positive but it is coming out to be negative? [closed]

I have described a question in which this problem arises in the image below:
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1answer
125 views

Conservation of energy or conservation of momentum- which one is applicable in this problem?

There was this question from Kleppner and Kolenkow's Classical Mechanics: PROBLEM: And I found its solution from this Link: It is quite an extended solution and I am not drawing you into the ...
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3answers
185 views

Gravitational Force [closed]

If energy is represented by Acceleration=A, then am=F ams=W (ams)/t=P Acceleration is always present when motion is present, acceleration is the energy. Since gravity translates into ...
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1answer
60 views

Moments question

The image is a body free-falling with two forces acting on it. If we take moments about A, we clearly get anticlockwise moments, and that is what will happen if this were to take place in real life. ...
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2answers
63 views
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2answers
180 views

What happens to the kinetic energy of a system in a non-elastic collision? [duplicate]

I know that the kinetic energy of a system is NOT conserved in a non-elastic collision. But energy is supposed to be conserved, so where does all that energy go? Is it transformed into other forms ...
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2answers
129 views

What's the right way to calculate power consumption over a month given a rate per minute?

When I was searching for power required to lift an object, i found that, for example: $100\ \mathrm{kg}$ to be lifted 3 metres in 5 seconds. (vertical) Answer: $$\begin{align} \text{mass}\times\...
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2answers
121 views

Can a glider maintain a constant forward velocity component?

I have a puzzle which asks me to consider a (engineless) glider descending at a constant rate and flying at a constant forward velocity (in still air). The question asks how to derive sink rate, $v_s =...
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1answer
313 views

Two bodies connected by a spring

I came across of a problem. It is about two bodies with equal masses connected by a spring with the coefficient $k$ and the length of $l_0$. Suddenly, a constant force $F$ is applied to the first body....
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3answers
73 views

How do gravity and normal force balance on an inclined plane?

Consider a block placed on an inclined plane. Drawing a free body diagram and applying Newtons laws, I get $N\cos A=mg$ as well as $N=mg\cos A$. Here one equation contradicts the other, could anyone ...
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3answers
28 views

Confused about potential energy problem

So I am trying to solve this problem: On spring hangs a 2 kg block. Spring stiffness coefficient is 400 N/m. How much spring expanded? My attempt to solve it: ...
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1answer
28 views

Constant pressure, constant wall thickness, expanding volume = explosion?

Just been idly thinking about a gas cylinder I sometimes use. Pressure is about 200 Bar, or roughly 20 MPa. If I kept the same thickness of steel wall, and the same pressure, but made cylinders bigger ...
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1answer
87 views

Coding Newton's Laws into C#. Having trouble determining the order of finding what I need

So I'm in high school, and I'm currently in AP Physics 1. We're currently doing Newton's Laws where we draw free-body diagrams and use all the various forces (Tension, friction, weight, that kind of ...
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4answers
406 views

How do I use the kinetic energy formula using mass as lbs and velocity as mph?

I understand that the formula for kinetic energy is: $(1/2)mv^2$, which is equal to 1 Joule or 1 N-m. If I want $m$ to be my weight (say 150lbs) and $v$ to be 40mph how do I apply it to this formula? ...
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1answer
24 views

How do I figure out how many N-m it takes to move a man on a skateboard?

Given that the skateboard is on a flat surface, and let's say that the man weights 150lbs. How would I figure out how many N-m it takes to move that man? Does the wheel size matter? Ignore friction ...
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3answers
92 views

Finding tension in string after pulley is pulled at an acceleration g

Two weights $W_1$ and $W_2$ are suspended from the ends to a light string passing over a smooth fixed pulley. If the pulley is pulled up at an acceleration of g, the tension in the string will be:- (...
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4answers
268 views

Motion caused by Internal force

I would like to clarify whether an internal force in a system can cause it a motion externally? My Physics teacher and also other tuitions in my area tell that only external forces can cause motion of ...
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2answers
75 views

Heat produced in collision [closed]

A 5-gram marble is moving at 5 m/s [N] collides with a 2-gram marble moving at 3 m/s [N]. Final velocity of 2-gram marble: 7 m/s [N] How would I find the amount of heat produced in this collision? ...
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1answer
44 views

Acceleration of two points problem (mathematical explanation)

There is a square board with two nails in corner A and B. We apply a torque $M$ to the square board. Nail A can move freely on a track only in the $x$ direction and B only in the $y$ direction. The ...
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1answer
128 views

A question on Newton's laws of motion [closed]

A force of $50N$ is required to push a car on a level road with constant velocity of $10m/s$. The mass of the car is $500kg$. What force should be applied to make the car accelerate at $1m/s^2$? I ...
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1answer
204 views

Why is only angular momentum conserved for a planet and not linear momentum?

Suppose a planet is moving in an elliptical orbit with the Sun at one of its focii. I know that the forces in existence will be gravity which provides the necessary centripetal force. Now my book ...
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1answer
86 views

Work done by friction opposing a force at an angle

Let's imagine there's a block of mass m sitting on a rough surface with a kinetic friction coefficient $\mu$. It's being pulled with a constant force $A$ at $h$ degrees above the horizontal and is ...
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1answer
78 views

Why, intuitively, are tension forces the same but opposite in a taut rope/string?

I'm having a little trouble understanding why conceptually the two oppose each other with equal magnitudes. Let's say you have two people playing tug of war, with person A on the left much stronger ...
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1answer
39 views

When do I use center of mass versus conservation of momentum?

For example, if you are given your velocity in a problem where you are standing on a block slab which is on top of ice, you would use conservation of momentum. On the other hand, a question about a ...
1
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0answers
16 views

Newton's Third Law? [duplicate]

I've recently met with this new law and the way my teacher worded is so off for me. Shouldn't the equal and opposite reaction cancel out the action because they are equal? Apparently not? Why?
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1answer
110 views

Balanced and Unbalanced Forces Help

I am a newbie pondering in Physics concepts. I just had a question about Newtonian physics. The reason why "everyday" objects come to a rest is because there are unbalanced forces working against ...
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4answers
488 views

Earth's Kinetic energy change

Earth's rotational speed varies. I have checked the data an found following Peaks; Year 1998, 23.May, the Earth rotated in 86400.0023738 seconds. At 9.July the rotation time of the Earth was 86400....
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1answer
64 views

Homework: Rope falling on scale [closed]

I think I have a solution for the following question, but it seems suspiciously simple to me: Suppose we have fixed a rope of Length $L$ and Mass $M$ at the ceiling such that the tip of the rope just ...
2
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1answer
110 views

How far will the bullet travel before falling back to earth? [closed]

First, the question: A particular high performance rifle cartridge can be fired with a muzzle velocity of 1200 meters per second. The rifle is pointed straight up. Assuming there is no air ...
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0answers
35 views

Why does a balance try to be horizontal? The moments are equal [duplicate]

Suppose we have an ordinary balance where equal weights are put in both sides. Now one side is slowly held down. When this force is not applied anymore, the balance tends to achieve horizontal ...
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1answer
215 views

Position of centre of mass during toppling

Does the centre of mass shift in any way when it's about to topple, because a body toppling would simply mean that the weight vector is acting in a direction towards a point on the surface outside the ...
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1answer
141 views

A problem related to Center of Mass?

A Man is standing on the ground( Mass m) next to a rope-ladder(length l) attached to a hot air balloon ( Mass 3m). If he starts climbing the ladder and covers half of the rope, find the distance that ...
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1answer
79 views

Why don't we include the adhesive and cohesive force while calculating rise in a capillary tube?

The contact angle of a liquid solid interface is explained by saying that the liquid surface must be perpendicular to the resultant of adhesive cohesive and gravitational forces acting on it, since it ...
1
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1answer
77 views

Understanding elastic collisions of objects with the same velocities

I am having trouble understanding the following statement from my book: The law of cosines tells us that if the sides of a triangle obey the Pythagorean formula, they must form a right triangle. ...
0
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2answers
121 views

Measuring a rotating shaft's torque [closed]

My question is, there is a rotating shaft and I want to measure its torque. I don’t know its $r$ and $F$ but I connected a thread to the end of shaft to see how much weight it can lift and it is 2 ...
0
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2answers
212 views

Can you take the integral of $ d^2x\over dt^2$? [closed]

I am messing around with physics problems, and as silly as this maybe how do you take the integral of $$\int_0^\infty xd^2x$$ For example taking Newton's Second law $F=ma$ $$ F=m{d^2x\over dt^2} $$...
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3answers
52 views

The formula for the kinetic friction on inclined surface

I'm confused about the formula for the force of friction on inclined surface. It says that $f$ (force of friction) = $\mu N$ (where $\mu$ is the coefficient of the friction). Is: $$f = mg\cos(a)\...
1
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1answer
90 views

Characteristics of a tight string

There was a question which I came across in newtons law of motion chapter in the physics book by H.C.Verma which was based upon simple atwood machine (atwood machine consists of two unequal masses ...
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1answer
42 views

Non-linear pendulum (Whittaker's treatise on analytical dynamics of particles)

Reading through Whittaker's "treatise on the analytical dynamics of particles and rigid bodies" I have a question regarding his analysis of the simple nonlinear pendulum at chapter IV. At some point ...
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5answers
4k views

How does Newton's third law apply to an object interacting with air?

We all know that if I punch the wall with $100\,\mathrm{N}$ force, the wall pushes me back with with $100\,\mathrm{N}$ and I get hurt. But if I punch air with $100\,\mathrm{N}$, does air punches me ...
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2answers
97 views

Spinning an object in vertical circle

The situation : A block of mass $M$ is tied to a string and is spun around in a vertical circle. The question asks me to calculate the tension in the string 'at the lowest point' after giving ...
2
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2answers
341 views

Throwing an object with air resistance

say I were to throw a 1 kg ball vertically upwards 100 m/s, with g=10 and also air resistance $0.01v^2$ . By considering the forces I can determine that the speed at which it lands is less than the ...
0
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0answers
33 views

Clarify throwing an object [closed]

Say I were to throw a 1 kg ball vertically upwards 100 m/s, with g=10 and also air resistance $0.01v^2$. By considering the forces I can determine that the speed at which it lands is less than the ...
1
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1answer
75 views

roller coaster with weight requirement for a car

My kids went on a roller coaster type ride on the weekend. The staff loading individual (separate) cars on the ride said each had a minimum and maximum requirement to clear a hill - too little, it ...
0
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1answer
67 views

push up weight distribution [closed]

I'm about 84 Kg, in push up position (hands on the scales) the scales show about 54 Kg. Can anyone explain briefly the physics of the weight distribution? (I did high school physics decades ago - can'...