Questions tagged [newtonian-mechanics]

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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What are two different angles we can throw a ball, so it lands at the same spot? [on hold]

This is not a particularly difficult task, but it has given me a lot of trouble and I can't solve it. We throw a ball at 60° angle with a speed of 20 m/s. The ball lands 35.2 m away. What is the ...
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Infinity problem in basic classical mechanics problem

My question arises from a classical mechanics problem from a Hong Kong physics training programme: This is not a homework question as I am not asking about how to solve the problems in the image. As ...
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1answer
20 views

How many ways can one possibly spin an object at the end of a string?

I had a job that required me to carry a set of keys attached to a chain for most of the summer. I found that I could spin my keys at the end of their chain in two ways: in a circle, and in a figure-8. ...
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4answers
114 views

Why the 2 other blocks have zero acceleration

I was doing an exercise and I was stopped after arriving to a question, 3 blocks A , B and C are attached between them by massless and frictionless strings, that passes through frictionless, ...
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1answer
18 views

How to find the acceleration of two blocks? [on hold]

Help I'm really lost. I'm not even sure what forumla im supposed to be using on this problem A 15 kg block is placed on top of a 25 kg block (see figure below). A force of 387 N is applied to the ...
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197 views

How does Lenz law conserve energy in this case?

A magnet is falling into the coil as shown. The current in the coil creates a magnet as shown ( by the right-hand grip rule ). Now, as the magnet falls towards the coil, the magnetic field strength in ...
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3answers
90 views

Physical reason for $T^2=a^3$ when $T$ is in years and $a$ is in AU

Kepler's third law states $$T^2\propto a^3$$ When $T$ is in years and $a$ is in AU, the proportionality constant becomes $1$. This can't be a coincidence; I would like to know the physical reason for ...
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140 views

Inconsistency of PE to KE conversion in moving reference frames

Here's a nice trick question to keep you amused over the weekend. A trolley of unit mass with light frictionless wheels is released to roll down a ramp onto a smooth level surface. The PE lost equals ...
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A heavy ball on a thin sheet of paper

If we keep a heavy metallic ball on a thin sheet of paper the paper is torn and the ball drops. But according to Newton's third law of motion every action has an EQUAL and opposite reaction. So when ...
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1answer
31 views

Spring constant of harmonic oscillator [on hold]

I got a task from my lecturer to solve a differential equation for a simple harmonic oscillator: $$m{d^2\vec{r} \over dt^2}=-k^2\vec{r}.$$ So far, I have managed to find this equation only in one book....
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Does the length variable in pendulum motion include center of mass?

In diagrams, is the bob/mass of the pendulum considered a point, or a 2/3D object? And furthermore, is the length variable in the period of a pendulum simply the length of the string, or is it really ...
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3answers
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Change of buoyant force as object moves deeper

When reading about Fluid Dynamics, I saw two questions that presented similar situations but had very different answers, and I'm trying to understand why, since they seem contradictory: A beach ...
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2answers
289 views

The torque created using an oval chain ring

I have seen the explanation on "How bicycle gear works?" but this seem to be using a standard round chain ring. I would like to know if there is any difference when an oval chain ring is used. As I ...
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2answers
377 views

Work done by air resistance

How can air resistance do work on a freely falling body on earth. then it's displacement is only due to gravity. I think Air resistance doesn't displace the body falling. So what is the meaning of ...
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1answer
67 views

Why does a falling object gain horisontal speed?

This really bothers me as I think I should know the answer... I pushed a toilet paper roll so it slowly rolled of a five centimeter edge. On the next surface it had gained a lot speed. But why? It ...
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627 views

Calculating rolling friction of a toy car's wheels, not on an incline

I'm dealing with a small toy car consisting of a bottle that has a small hole in the back, covered by a thumb tack. The bottle is filled with pressurized air then the thumb tack is released, releasing ...
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2answers
50 views

If a ball is kept on the table, then what forces are being exerted on it?

If a ball is kept on a table then there is gravity acting on it as well as a normal reaction force by the table on the ball. But as both the forces are being exerted on the same object i.e. the ball, ...
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0answers
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Classifying all symmetries of a mechanical system [duplicate]

Given a newtonian mechincal system with $n$ objects, we may think of it as living in $\mathbb{R}^{6n+1}$ ; one dimension is time, $3n$ dimensions for velocities, and $3n$ for positions. We then have ...
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1answer
51 views

Satellites orbiting around any planet's [on hold]

Suppose a satellite is revolving around a planet with radius r. Now if we increase the value of r then the angular velocity and kinetic energy will decrease, but the total energy & potential ...
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Y the relation among centripetal, centrifugal and gravitational force exerred on the moon is different from an object on the earth surface?

I read that since the earth vid rotating on its axis ,an object on the earth surface experiences a centrifugal force because the object is also moving around the earth's axis.So,that centrifugal force ...
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1answer
36 views

Banked curve problem in another frame of reference

How would you set up Newton's equation of motion for this problem (rolling without slipping in a circular path) using the frame of reference shown in the figure:
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5answers
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Is acceleration an absolute quantity?

I would like to know if acceleration is an absolute quantity, and if so why?
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Directions of static & kinetic friction?

Static friction : Static friction opposes relative motion between two surfaces. The car is moving at some tangential velocity relative to the road. Thus, static friction should act in the opposite ...
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How can i calculate the friction force in this problem? [closed]

Question: if the engine of a 1400kg car uses 25kw to maintain an average speed of 17m/s, calculate how much friction is acting on the car. my try: p = $\frac{w}{t}$, w = ΔKE, KE = $\frac{1}{2}mv^2$...
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When applying the equation of torque and equating it to $I\alpha$ which moment of inertia do we take?

I believe $T=I_{cm}\alpha$, where $I_{cm}$ is the moment of inertia about centre of mass and $\alpha$ is the angular acceleration. But do we take $I_{cm}$ even if the torque has been taken about a ...
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1answer
64 views

Find $v(t)$ and $x(t)$, How do I treat $δt$? [on hold]

We apply a force to a particle with a mass $m$ and inicial velocity $v_0$: $$ F(t) = \left \{ \begin{matrix} 0 & \mbox{ $t<t_0$} \\ \frac{p_0}{\delta t} & \mbox{ $t_0<t<t_0 +\...
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2answers
173 views

Spinning top fixed point

I have seen many explanations about the movement of a spinning top. The explanations were in a varied level, from basic newtonian mechanics to Lagrangian formalism. But I do not understand why some ...
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2answers
29 views

Work done by a varying angle

I know that work done by a constant force is $W=\vec{F}\cdot \vec{x}$, and that work done by a variable force is $\int \vec{F} d\vec{x}$. However, how do you calculate work done by a varying angle?
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17 views

Maximum Distance [closed]

An object with mass m moves straight in a flat plane and gets a resistance force f = - kv,. If at t = 0, v = 2m / s and at t = 3 s, v = 1m/s . Determine the maximum distance that the object can travel?...
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2answers
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Confused about the origin of the Coriolis effect when moving along the equator

I'm taking an introductory course on meteorology and in the lecture notes there is an explanation of the Coriolis effect that confuses me. The components of a wind field are u, v and w: $\vec{U} = u \...
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3answers
261 views

Net Force on System Not Equal Zero, but GPE increases and no change in Kinetic Energy

I am confused about changes in gravitational potential energy, net external force, and work-energy theorem. For a single particle system, I understand that a net external force results in a change in ...
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2answers
137 views

Confusion about angular momentum of earth-moon system

My assumed definition of angular momentum is the sum over $i$ of $L_i =r_i\times{\omega_i}\times{r_i}$ for each particle about some origin. We have two spheres rotating about the centre of orbit. For ...
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About the movement of a particle attached to a string [closed]

One particle (with mass m) is attached with a string to a circumference which is the base of a cilinder of radius R. If we give v_0 to the particle and it moves in the XY plane of the base of the ...
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0answers
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Tangential orbital perturbations [closed]

A satellite, m, orbits in an ellipse with semi major axis a and eccentricity e (let i = Ω = ω = 0). A small, constant tangential force F (tangential) = f, is applied to the satellite. Find an ...
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1answer
109 views

Newton's Third Law of Motion? [duplicate]

Newton's third law of motion states that every action has an equal and opposite reaction. But, on punching a wall, I feel much greater force than on punching an inflated balloon. So, what does it mean?...
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What is the most optimal cost effective diameter of a hyperloop tube ferrying ALL cargo between the US and EU? [closed]

what is the most optimal cost effective diameter of a hyperloop housing vacuum tube housing hyperloops that can ferry ALL cargo currently travelling by air and sea to and from the US and Europe? ...
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4answers
94 views

When is work actually done?

Wikipedia says: For example, when a ball is held above the ground and then dropped, the work done on the ball as it falls is equal to the weight of the ball (a force) multiplied by the distance to ...
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0answers
23 views

Ratio of the gravitational force that Earth exerts on the Sun [closed]

What is the ratio of the gravitational force that Earth exerts on the Sun in the winter and the force that it exerts in the summer in the Northern Hemisphere? Hint: Earth's orbit is an ellipse with ...
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1answer
352 views

Tension and Angular Momentum Equilibrium (Exercise)

I have this exercise that i'm trying to understand: A bar AB with a negligible mass is put on an edge, the masses $m_1,m_2,m_3$ are lied to the bar through inextensible wire(negligible mass) and a ...
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1answer
72 views

Navier-Stokes Derivation

Someone knows where can I found a physical derivation of the Navier-Stokes equation? Mainly the stress tensor. A lot of authors simply "jumps" the stress tensor and it's the more important of physical ...
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5answers
55 views

Does it take more force to press two springs in series?

Let's say I have a spring that takes force $F_1$ to fully compress it from a relaxed state with spring constant $k_1$ and total displacement from relaxed state $x_1$, which I believe is related ...
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1answer
29 views

Very Basic Q on Hooke's Law Problem Pt.2

"A uniform beam AOB, O being the mid point of AB, mass M, rests on three identical vertical springs with stiffness constants k1, k2 and k3 at A, O and B respectively. The bases of the springs are ...
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4answers
85 views

Why does body with continuous speed generate force?

So... sorry if the question seems a bit stupid, but it's been nagging me all day and I couldn't find an answer on the net. It goes like this: If a body, say, a car is moving with constant speed. This ...
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3answers
97 views

Motion of a boat in a stream

We are doing problems involving boats sailing from one shore to the other. Usually, in such problems we are told the velocity of the boat with respect to the water and the angle at which the boat sets ...
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1answer
42 views

Kinematics and point mass

In which of the following body can be considered point object A railway carriage moving without jerks between two stations. A monkey sitting on top of a man cycling in a circular path. A spinning ...
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2answers
39 views

A question about an assumption on a Very Basic Hooke's Law problem

A question states: A uniform beam AOB, O being the mid point of AB, mass $M$, rests on three identical vertical springs with stiffness constants $k_1$, $k_2$ and $k_3$ at A, O and B respectively. ...
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2answers
59 views

Where to put weight so that 2 jointed rods are most likely to slip? [closed]

I'm doing the attached mechanics question for school and would like to know exactly why you the man standing in the middle of the system increases the likelihood of the system slipping. The solution ...
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1answer
28 views

Power of conveyor belt required to accelerate a mass

Assume the following scenario: A conveyor belt is driven at velocity v by a motor. Sand drops vertically onto the conveyor belt at a rate of $m$ kg/s. What is the power required to move the belt at ...
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2answers
54 views

Static and Kinetic Friction on an Incline [closed]

A box is launched upwards along a $30^o$ incline that is $1.0 m$ long. How far from the edge of the incline will the box reach if its initial speed is 3.55 m/s. The coefficients of of static and ...
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1answer
236 views

How to approximate this simple harmonic motion?

In the assembly shown in the figure, both the pullies are massless and frictionless on their axes. The positions of the strings are adjusted in such a way that, in equilibrium position, springs $k_1$ ...