Tagged Questions

The product of the force on an object and the displacement the object undergoes along the direction of the force.

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1answer
29 views

Work energy and laws of motion and friction problem?

I am having a confusion in the following question- Q-To stimulate car accidents auto manufacturers study the collision of moving cars with mounted springs of different spring constants. consider a ...
0
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1answer
27 views

Power - 1/2 Force x velocity? [on hold]

A pump, taking water from a large reservoir, is used to spray a jet of water with speed 20m/s. The nozzle of the pipe has radius 0.05m, and is level with the surface of the reservoir (no change in ...
6
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4answers
381 views

Is there a fundamental reason not to define the work vice-versa

My question arises from something which has never been really clear: in continuum mechanics, why is strain energy defined as: $$W=\int_\Omega ...
1
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1answer
33 views

Work done in case of an accelerating object [on hold]

How do you calculate work when opposing force is less than applied force. So a 5 N static friction force is overcome by 15 N manual force for say 5 meter. What is the work done by manual force?
0
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0answers
30 views

Work done in isothermal process [on hold]

So I am mightly confused with work done in thermodynamics. Need some help pls.. What is work done in below two cases (Isothermal) Ireversible 1) Expansion of gas against atmosphere pressure. No ...
-4
votes
1answer
33 views

Mechanics, work, spring [on hold]

I'm off by a factor of 2 according to the solutions, but I can't see why. Question: A force of 800N stretches a (weightless, horizontal) spring by a distance of 0.200m. What is the potential ...
0
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1answer
20 views

Solving kinetic energy exercise through electrical work formula instead of voltage formula?

While studying electric potential, I run into an issue on exercise 43 of Chapter 24 of Fundamentals of Physics 8th ed. Vol. 3 (Halliday et al.). The exercise states the following, paraphrased: A ...
2
votes
2answers
37 views

Is the coefficient of restitution frame independent and energy conservation?

In this question I am ignoring relativistic effects. The following statements I think are true: change in Kinetic energy is not invariant under change of frame Force is invariant under change in ...
2
votes
1answer
29 views

Separating the potential energy of a system of particles.

Assuming all forces derive form a conservative source and that all forces observe the strong form of the third law, how do we arrive at the following equation? \begin{equation} V=\sum _i V_i+\frac ...
0
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2answers
156 views

If Earth starts moving when attracted by an object, where does the energy come from?

Suppose a body(very big but not bigger than Earth) moves against gravitational force of Earth. The force will do negative work on the body decreasing its kinetic energy. The decreasing energy is ...
10
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6answers
628 views

Why does a conservative force return the work done against it by a body to that body?

Newton's 3rd law of motion: Newton's third law of motion or the law of action and reaction implies that there is no isolated force in nature. Whenever there is any force at all , there must be ...
2
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4answers
138 views

Kinetic energy vs. momentum?

As simple as this question might seem, I failed to intuitively answer it. Let's assume there is a $10,000$ $kg$ truck moving at $1$ $m/s$, so its momentum and KE are: $p=10,000$ $kg.m/s$ and ...
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2answers
45 views

Line integral calculates work, even though the force from the vector field doesn't cause the movement?

I'm afraid the title here was unclear, so I'll attempt to make things a bit more clear. I am conceptually confused about the physical meaning of line integrals over a vector field, so I'll pick an ...
3
votes
5answers
224 views

A force is exerted on a body, kinetic energy increases but no work is done by the force. Why?

After reading the article, I was totally perplexed . I was reading the External forces and internal energy transfers in Principles of Physics by Resnick,Halliday,Walker. It goes like that An ...
0
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6answers
316 views

Why is kinetic energy stored as potential energy in a body during its motion against gravity?

Everyone knows kinetic energy is converted to potential energy in the body when it moves up against the earth's opposing gravitational force. But I am facing some problem with this. What I learnt ...
0
votes
1answer
21 views

Final velocity of a spring [closed]

I need to calculate the velocity of an object when it is thrown by a spring; we have to calculate the velocity from $U=\frac 12 kx^2$. Now I know that $U=L=F\cdot S$ and $S=\frac{v_f^2-v_0^2}{2a}$. ...
4
votes
3answers
230 views

Why is it mandatory to lose energy to an opposing force?

A body must do work against an opposing force to continue motion. I have found this statement many times. But what is the reason behind it? Suppose $F_1$ is acting on a body to accelerate it (to ...
4
votes
2answers
191 views

What's wrong with my derivation for the spring constant? [duplicate]

An $8.00\ \mathrm{kg}$ stone at rest on a spring. The spring is compressed $10.0\ \mathrm{cm}$ by the stone. What is the spring constant? I used conservation of energy to solve this problem. The ...
0
votes
1answer
70 views

Difference between heat and work

According to the Kinetic Theory of Matter, temperature is nothing but a measure of the kinetic energy of matter. My textbook says that the change in internal energy of a system is the heat gained plus ...
1
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2answers
32 views

Confusion with Grounded Conductor: bringing in a point from infinity

Suppose, for sake of argument, we have a spherical grounded conductor at the origin. Additionally, let our reference voltage be at infinity. Now, I view the potential of a point in space as being the ...
1
vote
1answer
108 views

Work Done in a Thermodynamic System (Cylinder with Piston) [closed]

Heated Piston A cylinder of cross-sectional area 0.0314m^2, filled with argon (a monatomic ideal gas), is sealed with a piston of mass M=25kg that is free to move up and down. The piston is ...
10
votes
6answers
2k views

How can energy be useful when it is 'abstract'?

The topic which haunted me for two years until I gave up on it. But now I am doing engineering and this topic suddenly popped out of my textbook from nowhere. I seriously need to understand this topic ...
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votes
1answer
34 views

how to use the energy work kinetic theorem [closed]

A single force acts on a $3.4~\text{kg}$ particle-like object in such a way that the position of the object as a function of time is given by $x = 4.2t - 2.1t^2 + 2.5t^3$, with $x$ in meters & $t$ ...
2
votes
3answers
172 views

Joules to do something

If my very limited understanding is correct, then, not accounting for gravity: 1 Newton can move 1 kilogram 1m But, can 2 Newtons move 1 kilogram 2 meters? Is this because 1 Newton = acceleration ...
22
votes
9answers
2k views

Why can we cycle faster than we can run? [duplicate]

This seems obvious: faster long-distance runners hit ~20 km/h (marathon records) while fastest cyclists can do ~40 km/h (Tour de France stats). But on the physical/biological level this doesn't seem ...
0
votes
1answer
68 views

Why does the magnetic force exerted by two charged particles on each other do no work?

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. ...
1
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2answers
44 views

The effect of windspeed on a car

I've worked problems in the past in trig class concerning the effect of wind on the speed of a plane and it's flight path and was wondering if a similar thing occurs with a car. First off, I'm ...
0
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2answers
97 views

Why isn't work relative?

Acceleration and displacement can be defined relative inertial frames. For example, a body moving with constant velocity on top of another moving with the same velocity will have zero displacement ...
1
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2answers
76 views

How can I understand how $\text{m}^2/\text{s}^2$ is related to $\text{J}/\text{kg}$?

$E=mc^2$ is the famous equation that states the equivalence of mass and energy, with a conversion factor in units of $\text{m}^2/\text{s}^2$. But in my naive mind, the conversion factor of mass and ...
2
votes
2answers
135 views

If an asteroid were threatening the Earth, could I deviate it just by jumping on it?

An impact by a 10 kilometres asteroid on the Earth has historically caused an extinction-level event due to catastrophic damage to the biosphere. There is also the threat from comets coming ...
2
votes
4answers
104 views

Why work $W$ and heat $Q$ are different concepts?

I understand heat as the flow of energy (through radiation, convection or conduction) from one body to another. When I think about conduction (for example) I visualize particles that jiggle a lot ...
4
votes
2answers
103 views

How to calculate wasted energy

Suppose you are pulling a weight along a track at an angle (in the picture 45°). If the object is dislocated by a distance $D_{45}$ let's assume that the mechanical work done on/energy transmitted to ...
3
votes
1answer
100 views

Could $\int (\ddot\phi + \mu\dot\phi^2)d\phi$ ever be negative? How to show it?

I am working on the following problem: Given a mass $m$ at rest at the base of an incline surface shaped like 1/12th of a circle with radius $R$. The mass is pulled up the incline by a rope that ...
1
vote
2answers
81 views

Work done against gravity [closed]

The work done against gravity is $mgh$, well at least that's what my textbook says. I have a question: I can apply a force say 50N, so total work done = $mgh + mah$. Where $ma$ = Force. But the truth ...
1
vote
3answers
68 views

Why does the work done by an internal force differ from the work done by external force?

Let's consider the following situation. We put a body of mass $m$ at a distance $A$ from the center of Earth. We let the Earth attract the body and analyze the situation at a point $B$, closer to the ...
2
votes
0answers
51 views

Connection: Work on dipole <-> optical absorption

If I consider a two-level system with a ground and an excited state, I can compute the instantaneous rate at which work is being done on the dipole $\mu(t)$ by an electric field $E(t)$: $\dot{W} = ...
0
votes
1answer
25 views

Comparing work done for two accelerations

Suppose at a time $t_{0}$ a car goes from 0 to 30mph at time $t_{1}$, and then maintains a speed of 30mph until $t_{2}$. After that minute it accelerates, reaching 60mph at time $t_{3}$. I want to ...
1
vote
1answer
262 views

Derivation of formula of potential energy by a conservative force [duplicate]

the formula for potential energy by a conservative force is given by: $$ F = -\nabla U(r), $$ which in one dimension may be simplified to: $$ F = -\frac{dU}{dx} .$$ My question is how is it ...
2
votes
1answer
160 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
0
votes
0answers
43 views

Work to Create a Vacuum

I'm trying to determine the amount of work required (in Joules) to create a vacuum of a certain pressure in a tube. A pneumatic cylinder will be used to remove the air from the tube to create the ...
1
vote
3answers
49 views

Work done by gravity on a ball & the ball on earth

I have studied today that if a ball was to fall a certain height, then the work done by gravity on the ball would equal the work done by the ball's equal and opposite gravitational pull. By $W=Fd$, ...
0
votes
5answers
209 views

Who does work while walking?

While walking the work done by friction is zero. But who does the work, actually? How someone is getting displaced? This situation also arises when someone climbs without slipping or is climbing a ...
0
votes
2answers
40 views

Special case of work done by two opposing forces of equal magnitude on a body possesing inertial motion

Consider an elevator moving upward with constant velocity. The constant velocity is maintained by an upward tensional force equal to weight. If we add the total work done on the elevator it will be ...
0
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3answers
84 views

Confusion relating the application of Work-Energy theorem

Could someone kindly explain the solution to my confusion? When we walk at a constant speed up a steep hill, is work being done? Then why isn't our kinetic energy changing as work done is equal to ...
1
vote
1answer
49 views

Action Reaction Pairs and Work

Say that a ball is sitting in front of a compressed spring launcher. The spring is then released. The spring applies a force on the ball for a certain distance. This force is accompanied by an equal ...
0
votes
1answer
30 views

What is the work done below proportional to? [closed]

A raindrop falls from a certain height to the ground, with a terminal velocity u. The viscous force is F = 6*3.14*n*r*v, where n is the coefficient of viscosity, r is the radius of the raindrop, and v ...
1
vote
2answers
82 views

What does $ {\bf F} = \frac{\mathrm{d}W}{\mathrm{d}{\bf x}}$ actually mean?

What does the formula $$ {\bf F} ~=~ \frac{\mathrm{d}W}{\mathrm{d}{\bf x}}$$ actually mean? Here $\mathrm{d}W$ is the work done in a small period, ${\bf F}$ is the force and $\mathrm{d}{\bf x}$ is a ...
0
votes
1answer
167 views

Computing average force exerted by ground when jumping

Problem: A man of mass $m$ jumps vertically into the air from a sitting position in which his center of mass (CoM) is at a height $h_1$. When his feet are just about to leave the ground his CoM is at ...
2
votes
3answers
112 views

What is the work done against a force?

Suppose a particle travels a path $\gamma : I\subset \mathbb{R}\to \mathbb{R}^3$ subject to a force $\mathbf{F}: \mathbb{R}^3\to T\mathbb{R}^3$, then we know that we define the work done by the force ...
0
votes
2answers
87 views

Find the minimum force that has to be applied to the block $m_1$ so that the other block just begins to slide

This is a problem from the book 'Problems in General Physics' by I E Irodov. Two blocks of masses $m_1$ and $m_2$ are placed on a rough horizontal surface, connected by a light spring. Find the ...