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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Confusion about Conservation of Mechanical Energy

I'm having a bit of difficulty understanding how to apply the idea of conservation of mechanical energy to a problem. One of the questions on my homework reads: A physics student shoves a 0.50-kg ...
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1answer
65 views

$P = h \rho g$ derivation

Here is a snapshot from my textbook : Here only three forces are calculated: The gravitational force The force due to the pressure $p$ on the bottom surface The force due to the pressure $p+\...
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1answer
34 views

Does a ball thrown down exert less force on the ground when we walk? [closed]

Scenario A: You stand still and throw a ball vertically down. When the ball hits the ground it exerts a specific force on the ground. Scenario B: While walking you throw a ball vertically down. When ...
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2answers
71 views

Find the relation between length of pulley and strings [closed]

A pulley is pulled with external force $F$. $x$ and $y$ denote the displacement of two ends of strings of the pulley and $z$ is the displacement of the pulley. Prove That $$z = \dfrac{x+y}{2}$$...
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110 views

Can torque relations actually be *derived* from Newton's Laws, or is it something extra?

For a long time I have wondered if there is a way to show that the rotational analogs of Newton's Laws are a direct consequence of just those laws, or are we adding more to them? I understand ...
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1answer
67 views

A simple explanation of Kepler's Third Law

Is there a simple way to explain how Kepler's third law follows from the inverse square law that of gravity (and laws of motion) For example for Kepler's second law we can say it's because Gravity ...
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28 views

Given Tension and the wave equation, how do you find the linear density?

I am given that the equation of a transverse wave of a string is y(x,t) = 2.00mm(sin(25.1rad/m)x-(415 rad/s)t) and the string is under 18 N of tension. From the tension, I got that the string is ...
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1answer
31 views

How can you calculate the thrust-to-weight ratio of a gun?

Is there some formula I can apply to the weight of a gun, along with the force of thrust it creates, and calculate if it will be able to lift itself off the ground or not? Without actually handling ...
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2answers
63 views

Why do tops move opposite to each other when colliding, not tangentially?

When two well-balanced tops collide, they tend to bounce directly away from each, in other words along the line connecting their centers. Intuitively I would expect the tops to move tangentially, not ...
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2answers
75 views

Why was it difficult to walk in the same direction the train's acceleration, and easier the other way around?

The other day while I was walking in the same direction that the train was accelerating. Then I came across this question. Please if would answer it, I am very curious to know. But when I walked the ...
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2answers
77 views

Is Keplers First Law a consequence of the conservation of angular momentum?

It would seem that once you have deduced that the angular momentum is conserved then you can deduce: $r^2\dot{\theta}=h$ is constant Combining this with the radial equation of motion then yeilds a ...
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1answer
77 views

Range of ballistic missile on flat world

The range of the Trident 2 submarine-launched ballistic missile is stated to be at least twelve thousand kilometres - the exact figure is classified, but taking it as 12,000 km exactly for purposes of ...
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0answers
26 views

How can I get the Resonant Frequencies (Bode plot)? (Response of 2-DOF System)

I want to study the response of the system. I want to find the resonant frequency of the sprung mass (m1) and the resonant frequency of the unsprung mass (m2). Because I am not sure if I have ...
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3answers
101 views

Velocity of a body in a pulley problem involving a spring fixed to the ground

So the picture shows the whole situation. My question is, how do you find the velocity of the object after it had descended 10 cm (0.1 m) ? Pulley's radius 0.2 m, moment of inertia 0.2 kg/m I have ...
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1answer
103 views

Why does a force parallel to the axis of rotation do not produce torque? [closed]

One explanation can be that Torque is a cross-product (r x F). I want to know what is its physical interpretation.
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2answers
39 views

Rotation of join of two different rods when one is rotated [closed]

Two cylinders A and B made of same material and having same length of radii $r$ and $2r$ are soldered coaxially. The free end of A is clamped and the free end of B is twisted by an angle theta. The ...
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2answers
59 views

Vector addition forces with law of cosine

Given two vectors $\mathbf{F_1}, \mathbf{F_2}$ and an angle $\alpha$ between two vectors we can derive the resulting force $F_R:=\Vert \mathbf{F_R}\Vert$. $$F_R^2=\Vert\mathbf{F_2}-\mathbf{F_1}\Vert^...
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1answer
48 views

Change in energy during orbital decay

Suppose we have a planet orbiting a star and the planet radiates away some amount of energy $\Delta E$. I want to find by how much the orbit decays (i.e the change in orbital radius). One way to do ...
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2answers
43 views

Problem with transforming co-ordinates to rotating frame of reference

In the following question: A puck is placed on a friction less disk that is rotating with angular velocity $\vec \omega$. What is the equation of motion with respect to the rotating frame of the puck?...
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2answers
49 views

Conditions to impose for accelerations in systems of rotating pulleys [closed]

I do not understand completely how do rotating pulleys with ropes (that do not slip) work. Besides the equations of motions, which are clear to me, some conditions on the accelerations are needed to ...
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1answer
44 views

Does the centrifugal force affect stationary objects as seen from the inertial reference frame?

If an object is moving at the same speed as a rotating/accelerating frame of reference it's in contact with but in the opposite direction (making its displacement zero), would such an object be ...
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0answers
46 views

Toricelli's law of efflux in moving container

Suppose there is a big tank of water with a small hole near the bottom. Now if this tank starts moving with say a velocity 'v', then will Toricelli's law hold? I tried directly applying Bernoulli's ...
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1answer
34 views

What are internal forces and how do you calculate them?

There are many questions similar to the below, where you need to find the internal forces. I find such problems very poorly worded and designed. First, what do they mean by internal forces? Is it the ...
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1answer
42 views

Kinetic Energy: Difference in energy for observers [duplicate]

Consider a stationary 10kg bike; if I apply a force of 10J then $KE=\frac{1}{2}mv^2$ so $v=\sqrt\frac{2KE}{m}=1m/s$. If we consider the same example again, but from the point of view of a stationary ...
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1answer
35 views

What is the tension in the spring when its overall length is 70 mm? [closed]

A spring obeying Hooke’s Law has an upstretched length of 50 mm and a spring constant of 400 N m-1. What is the tension in the spring when its overall length is 70 mm? My solution: 400/50*70=560NM is ...
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2answers
285 views

How much more “work” (or energy) is required for short people to hike uphill?

Let's assume Short Person is 5 feet tall and the Normal Person is 5 feet and 8 inches tall. Let's assume the uphill hike has steps with 1 foot height. How much more work or energy does this require ...
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1answer
47 views

What is the relationship between $W_1$ and $W_2$? [closed]

I have a model which schematic is in the linked picture. Blue $A$ and $B$ are rotational joints, black and red shapes are rigid elements. $I_1$ is moment of inertia of black and red elements combined ...
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1answer
45 views

Newton's second law of motion and viscosity [closed]

In a Coutte flow, the applied force on one of the plates can be expressed by $F = \eta A \frac{dv}{dz}$. F here can also be defined using Newton's second law of motion, $F = m \frac{dv}{dt}$. The ...
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1answer
173 views

Projectile time of ascent not equal to the time of descent?

Why is the time of ascent less than the time of descent in a projectile motion. I understand that while going up the air resistance and gravity act downwards and while coming down gravity is ...
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1answer
105 views

Inelastic collision problem [closed]

A car of mass $1400$ $\mathrm{kg}$ moving south at $11$ $\mathrm{ms}^{−1}$ collides into another car of mass $1800$ $\mathrm{kg}$ moving east at $30$ $\mathrm{ms}^{−1}$. The cars ...
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1answer
99 views

What is meant by conservation of momentum? [closed]

I need proof of this. Some examples are also required.
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4answers
69 views

What makes the magnitude of the force of friction velocity dependent in one scenario, but not the other?

When a solid objects makes contact with another solid object, I believe the magnitude of the force of friction between them does not depend on the relative speed of the two objects. When a solid and a ...
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1answer
55 views

What is the resistance force of a ramp?

I know that the effort force is what you exert on the object, the effort distance is the length you walk on the ramp, and the resistance distance is the height that I traveled (or height of the ramp), ...
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2answers
116 views

How can I find the height for a looping pendulum? [closed]

I have a ball attached to a string, hanging on a rod placed $L$ meters above the floor. I release the ball and string at a 90 degree angle and let it loop around another horizontal bar after it ...
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1answer
33 views

Toppling and Torque related to it

When a body is said to be being just about to topple about one of its edge due to a force F applied, why do we not consider the torque of normal about the edge point but about the centre of mass? Are ...
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0answers
9 views

What is the analytical approach for a fiber cutting machine?

Folks, so today in the Lab I came up with this problem (see picture). It shows a cross section of a cutting machine. There's a blade moving with a constant speed dx/dt towards the center of the roll ...
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2answers
101 views

A question about the famous bucket experiment

Suppose that we have a bucket containing two liquids with different densities.Suppose also that i connect the bucket with an electric motor and i rotate the bucket. Why when the bucket rotates, the ...
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2answers
117 views

Difference between potential centrifugal energy and rotational/kinetic energy

I'm having troubles to understand the difference between kinetic energy and potential centrifugal energy in some situations. I make an example where I am confused. A object moves on a rod attached ...
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2answers
47 views

Problem with variation of velocity, doubt on the work energy theorem

I think I did not understand the use of the work energy theorem. Here is a situation I am confused about. Consider an object moving in the $xy$ plane with a constant velocity $\vec{v_0}$ at an angle $...
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2answers
270 views

Why does something on an inclined plane move forward at all?

We just started studying about the inclined plane and vectors in motion, but i don't understand one thing: Why on earth does the object on the inclined plane move forward (I.e in the direction where ...
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1answer
97 views

Rocket equation derivation mistake by my professor

In one of my lectures our physics professor gave a derivation of the ideal rocket equation as follows: Let $v_G > 0$ be the velocity at which the gas is emitted from the rocket. Let $m$ and $v$ be ...
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2answers
67 views

Free falling and bouncing back

My confusion arises with free falling body. For a free falling body the displacement ~ time graph has a kink (at the time when the body hit the ground ). at a kink point, a function is not ...
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2answers
181 views

Elastic collisions and 90 degrees angles [closed]

Why is it that if the angle between the two objects that collided together is 90 degrees then it must be perfectly elastic? Is there any theoretical proof other than convention?
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1answer
46 views

Note and homework organization [closed]

I am currently in a mechanics class and have some trouble trying to figure out how I should structure my lecture notes and my homework. I recently began rewriting my notes after class but I am still ...
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0answers
47 views

About the formula of pendulum simple

for the modulation and the simulation of a pendulum simple , I'm Find this formula : a(t) = a0 * sin ( sqrt(g/l) * t * Pi/2 ) - [ k/(mll) * cos ( sqrt(g/l) * t * Pi/2 ) * t ) ] ...
3
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2answers
135 views

Effect of friction on a moving body under a variable force

Given the system in the figure: The block slides on a horizontal surface and is acted upon by a force $P$ which varies in magnitude as shown. Knowing that the coefficients of friction between the ...
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2answers
100 views

Why can't we put an object anywhere in the earth's orbit around the sun instead of Lagrangian points?

If we place an object in the earth's orbit around the sun, it should have the same orbital period right? For example, what would be the behavior of an object in orbit at point A1? It is at the ...
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1answer
58 views

How does paddling in the water help a boat move forward?

The way I've seen it explained is like this: it all has to do with Newton's third law. However, the "equal and opposite" reaction predicted by the third law acts on the paddle - which is not ...
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0answers
31 views

What is the equation for the position of a falling body as a function of time? [duplicate]

I know that near the surface of the earth a projectile's position follows a parabolic curve in function of time because the acceleration is constant (about 9.8 m/s2). However, acceleration ...
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4answers
93 views

Would running along Earth's Surface at escape velocity cause you to get out of the Earth's gravitational pull? [duplicate]

If one were to run/drive/fly along the earth's surface (by this I mean tangential to the Earth) at escape velocity (about 7 miles per second), would that person escape the gravitational pull? If not, ...