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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3k views

Will the box move?

Here is a man in a box with wheels on a frictionless surface. Case 1 - The person constantly pushes the box while standing near its wall. Why doesn’t it move? (I know it is because of the 3rd law, ...
0
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1answer
161 views

Why does mass not matter on how quickly an object falls? [duplicate]

I've seen all the mathematical proofs and physics demonstrations in vacuums. However, for example, if a hammer falls to the Earth it falls very quickly. But, it can be interpreted another way. The ...
2
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2answers
71 views

Why is Work not equal to 625 Joules in this case? [closed]

A variable force $\vec{F} = 3x^2y \vec{i}$ (unit vector) is acting on an object that travels on a square loop in a clockwise direction starting from the origin to (0,5) then (5,5) then (5,0) then back ...
6
votes
1answer
273 views

Intuitive Explanation of Tippe Top Effect?

A friend showed me a tippe top (a special kind of spinning top) lately and asked me about the physics behind it. I thought about it for a while but cannot quite figure it out. So I will throw the ...
4
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3answers
2k views

Where does the energy go in a rocket when no work is done?

While playing Kerbal Space Program, I wondered where my chemical energy would go when fired at 90° to the motion. It would do no work on the rocket, but all that energy has to go somewhere, right? ...
0
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1answer
82 views

Law of inertia, Frames of reference

Ok, we all know that an Inertial frame of reference is defined like this: "An inertial frame of reference is one frame where Newton's First Law holds, therefore, a body has a constant velocity or ...
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1answer
81 views

Work done by gravitational force!

Suppose a ball is $10m$ high from the ground. It will have $E_p = 10mg$. Now, if the ball falls freely then we know $E_k$ will be $0.5mv^2 = E_p$. But it is said that the work done by a force will ...
2
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1answer
77 views

Why can we model a body to have a center of mass?

I accept that bodies have a center of mass. I also accept that if I were to suspend a body by only supporting it at its center of mass, then the body wouldn't rotate. In the scenario that we suspend a ...
1
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2answers
52 views

Simultaneous: static friction and acceleration

I need help thinking about two events happening simultaneously. I have a heavy block on a surface with static and kinetic coefficients of friction, though they are unknown. The block is connected to ...
-1
votes
1answer
56 views

Change in F vs x graph if spring is torn in half? [duplicate]

The force required to stretch a spring varies with the distance as shown in the figure. If the experiment is performed with the above spring of half the length, the line OA will: (a) shift toward ...
0
votes
2answers
55 views

Throwing a Ball from the ground

We know that the Potential Energy is equal to Kinect Energy for any object Thrown from the ground. Not in a straight way of the words. But in the a especific case when I use my my arms to throw a ...
-1
votes
1answer
244 views

Rocket projectile motion problem [closed]

I'm not really sure where to start with this question: In a brisk wind from the south-east of $14.1\:\mathrm{m/s}$ a rocket pointed due north is launched from a cliff that is $500\:\mathrm{m}$ above ...
1
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2answers
1k views

Instantaneous Centre of Rotation

Let's say a body is undergoing both rotational and translational motion. I know that ICR of the body as a whole will be the point about which the body is doing pure rotation, so basically will be the ...
0
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2answers
52 views

Why can we find forces like this using energy methods?

Often to calculate forces in complex situations (usually involving complicated mathematics), I have seen various people employ energy methods. The answer comes out correct, but I can't understand why ...
0
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2answers
157 views

Terminal velocity of a sky-diver [closed]

A $75~\text{kg}$ skydiver can be modelled as a rectangular "box," with dimensions $20~\text{cm} \times 40~\text{cm} \times 180~\text{cm}.$ Given the conditions we may use $F_\text{drag}= ...
2
votes
3answers
302 views

Why are triangles drawn like so when working with gravity on an inclined plane?

This is my first year as a physics student, and I've never learned about vectors past a basic level, so this is confusing me. When we have gravity on an inclined plane, we separate it into two ...
3
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4answers
342 views

Can infinite work be done?

Wikipedia defines work as follows. In physics, a force is said to do work if, when acting on a body, there is a displacement of the point of application in the direction of the force. Also work ...
0
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2answers
41 views

Frames of Reference in a Rotational System

Imagine two concentric rings with different diameters. One is spinning within the other. There is a small gap between the outer diameter of the inner ring and the inner diameter of outer ring. From ...
0
votes
1answer
35 views

Expansion in differential equation (rapid oscillating field) [closed]

Can anyone explain me how to derive the equation in (30.4)? I don't understand what approximations or substitutions are exactly performed.
0
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1answer
76 views

Why does $v^2=cad$ by dimensional analysis rather than $v^2=ad$? [closed]

Constants are generally added in functions to adjust for when magnitudes don't contain information necessary to the accuracy of the equation. Why is it that $v^2=cad$ instead of $v^2=ad$? What ...
1
vote
1answer
68 views

A teaser on center of mass of right circular cone?

How can a distinction be made between the centre of mass of a right circular cone As a uniform solid ($\frac{h}{4}$ from base, where is $h$ is height) and That composed of infinitesimally small ...
0
votes
1answer
38 views

Proving conservation of energy (kinetic + potential) in classical mechanics for an arbitrary system of particles?

For the case of a single particle in a potential $V$, it's simple : ${d\over dt} [{1 \over 2}mx(t)'^2 + V(x(t))] = mx(t)'x(t)'' - F(x(t))\ x(t)' = mx(t)'x(t)'' - mx(t)''x(t)' = 0$ But what about for ...
1
vote
3answers
81 views

Prove that the spacetime interval is not invariant under Galilean transformations [closed]

The spacetime interval $(\Delta s)^2 = (\Delta x)^2 + (\Delta y)^2 + (\Delta z)^2 - c^2(\Delta t)^2$ is invariant under the Lorentz transformation and this isn't the case for the Galilean ...
0
votes
3answers
553 views

Pendulum's motion is simple harmonic motion

For a pendulum's motion to be simple harmonic motion (S.H.M.) is it necessary for a pendulum to have small amplitude or S.H.M. can be produced at large amplitudes as well? If it is really necessary ...
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votes
1answer
45 views

I do not know whether i have solved this correctly. Can anyone help? [closed]

A cart is moving along the $x$-direction with a velocity of $4 \;\mathrm{m/s} $. A person on the cart throws a stone with a velocity of $6 \mathrm{m/s}$ relative to himself. In the frame of ...
1
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1answer
136 views

How are the watt-second, the newton-meter and the joule different?

The joule is $\mathrm{kg\,\ m^2/s^2}$ right? The watt-second is $\mathrm{J/s} \times \mathrm{s}$ thus $\mathrm{J}$. The newton-meter is $\mathrm{kg \,\ m/s^2} \times \mathrm{m}$ thus $\mathrm{kg \,\ ...
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1answer
68 views

Motion on inclined plane

What has to be the conditions for an object of mass $m$ to move down an inclined plane with uniform velocity in terms of the forces acting in different directions on the object?
0
votes
1answer
68 views

What do we mean by the “load” on an engine?

In engines, we often talk about the load being something that acts against the rotating of the crankshaft. However, what does this mean in real life? In a car engine, for instance, what would the ...
0
votes
1answer
55 views

Driven harmonic oscillator problem : change of variables and expressing the extension of the spring

I'm struggling to understand the reasoning in question $b)$. Basically, I had to write Newton's Second Law and do a change of variables to put the equation of motion of a mass $m$ in a specific form, ...
0
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1answer
283 views

Spring-block system, simple harmonic motion, time period

In the case of simple harmonic motion of spring block system, why time period of the simple harmonic motion of the block is independent of acceleration of the system (spring-block system)?
0
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1answer
47 views

Newton's law of motion, pseudo force

Can we feel pseudo force just like the real forces?
1
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1answer
56 views

Distance between coils on a massive spring

I'm trying to calculate the separation between coils on a massive spring with no weights attached under different conditions. I will present my solution to the problem in the case of a uniform ...
0
votes
1answer
364 views

Finding torque due to normal force [closed]

A cubical block of mass $m$ and edge length $a$ slides down a rough inclined plane of inclination $\alpha$ radian with a uniform speed. Find the torque of the normal force acting on the block about ...
-2
votes
1answer
39 views

Time in a vertical circular motion [closed]

How can I calculate the time taken to go from one point to another, in vertical circular motion? If we have radius, angle between 2 points, and initial velocity. I tried to write $\frac{dv}{dt} = g ...
0
votes
1answer
31 views

Water Flowing In And Out Of A Basin

After a tap above a rectangular basin has been turned on, the basin fills in a time T1. After the tap is closed, opening a hole at the bottom of the basin causes the basin to empty in a time T2. If ...
2
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1answer
72 views

The role of mass in the tablecloth trick

Apologies if this has already been answered, but I have a question about the role of mass in the classic tablecloth trick, where the demonstrator pulls the tablecloth out from underneath a set of ...
4
votes
4answers
2k views

Why is normal force perpendicular?

I realize "normal" is just another word for perpendicular, but semantics aside, what causes normal force to be always perpendicular to the plane? For example, on an inclined plane, why is it that the ...
-1
votes
2answers
106 views

Calculate the Earth’s velocity in its orbit (assumed to be circular) around the Sun [closed]

Data: GM of the Sun: $\text{GM} = 1.327 \times 10^{20} \;\mathrm{m^3 s^{-2}}$ Radius of the Earth’s orbit: $r_{Earth} = 1.496 \times 10^{11} \;\mathrm{m}$ Orbital period of a planet in seconds: $T = ...
1
vote
1answer
93 views

Whether a large or a small ball fall faster in the air?

Given a ball falling under gravity is subjected to air resistance, after performing a differential to the drag equation, I get: $$g-Z(v^2)/r = a = v',$$ (where $Z$ is a constant.) How can I know ...
0
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2answers
128 views

How do you choose direction of moment of inertia?

If a car is accelerating forward from rest with no air resistance while weight and normal forces act on the wheels, in which direction is the moment of inertia? Is it positive, clockwise or anti ...
0
votes
1answer
45 views

What's the average speed (along $z$) and the average position (along $z$) of an object in free fall?

I'm looking to calculate the average speed (along z) and the average position (along z) of an object in free fall. The initial instant is $t_0$ and we have: $z(t=t_0)=z_0$ $v_z(t=t_0)=v_0=0$ I ...
2
votes
1answer
218 views

Why does the rule that elastic collisions are at 90 degrees in 2 dimensions not apply?

When one object collides with another object of the same mass in a 2D plane, we know that we can derive that the angles that the objects leave the collision at add up to 90 degrees in a perfectly ...
0
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2answers
87 views

Why is kinetic energy calculated using speed?

Why is kinetic energy calculated using speed? Since speed is distanced covered, and if a car moves 100 meters around a circular track -- stoping after moving half of the distance of the track -- the ...
1
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1answer
183 views

Spring rotated in uniform circular motion

Why does a spring stretch when rotated in uniform circular motion? The horizontal rod containing the massless spring(stiffness = k) and block of mass 'm' is rotated uniformly about point P. ...
5
votes
5answers
1k views

Zero gravity means zero friction?

The frictional force acting on a body placed on a horizontal plane is $F=\mu{R}$ where $R$ is the normal reaction and is equal to weight of a body in this case. And $\mu$ is the coefficient of ...
1
vote
1answer
493 views

Center of mass (COM) of a uniform quarter disk [closed]

I was trying to calculate the coordinates of the COM for a uniform quarter disk. By symmetry, it must lie on the angular bisector of the central angle. Also, $A=\frac{\pi R^2}{4}$, thus ...
0
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3answers
52 views

Multi-Force Lift

Background: I am creating a 3D game. A ship has 3 thrusters that apply force up (Z+) to counteract the force of gravity (Z-). I am trying to figure out how much thrust to apply to each thruster to ...
1
vote
1answer
65 views

Contradiction of total energy of a system? [duplicate]

I consider a situation in a system in which an observer is sitting in body of mass $M$ and another observer in a body of mass $2M$, both moving with velocity $v$ towards each other. If observers in ...
2
votes
1answer
52 views

Potential Energy in a System and its Relation to the Total Energy

In this answer it was stated that potential energy is a property of a system and not an individual particle. If we have two particles (1 and 2) interacting via a conservative force, we can write an ...
0
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0answers
121 views

How to measure the initial velocity of a potato gun?

I have made a 2m potato gun (It's like a cannon - the noise makes your ears buzz for some second :) ) Its uses alcohol as fuel. an igniter fires. then the potato will be shot out. anyway. as it's ...