All Questions
70
questions
2
votes
0
answers
141
views
What is the status of the Work-Energy Theorem? [closed]
All the 'proofs' of the Work–Energy Theorem that I have seen show that the work done by the resultant force acting on a body is equal to $\Delta \left(\tfrac 12 m v^2)\right)$ for that body. [It's ...
- 36.1k
0
votes
3
answers
432
views
Goldstein: derivation of work-energy theorem
I am reading "Classical Mechanics-Third Edition; Herbert Goldstein, Charles P. Poole, John L. Safko" and in the first chapter I came across the work-energy theorem (paraphrased) as follows:
...
- 232
1
vote
2
answers
403
views
Work Done on a rotating thin rod by hinge Forces
So I was studying the concept of rotational energy through a video, and the guy presented a problem,
It's like this:
"Suppose a thin rod of mass M and length L/2 is hinged from one end. Then, it ...
- 444
0
votes
1
answer
45
views
Is the definition of work related to the nature of the fundamental interactions?
I am having troubles trying to understand why is work defined as it is.
So, I know how work is defined: $W = \vec{F}\cdot{}\vec{d}$ (F is the force, d the displacement) and I am okay with it. This, ...
- 23
0
votes
0
answers
689
views
Lagrangian intuition [duplicate]
I am new to lagrangian mechanics and it just baffles me the idea of subtracting potential energy from kinetic energy. Why don't we use kinetic energy alone and the least action path (between two ...
- 105
0
votes
2
answers
96
views
Is net force conservative?
From the work-energy theorem, $$\int_{C}^{}\vec{F}\cdot d\vec{r}= \frac{1}{2}mv^2_f -\frac{1}{2}mv^2_i$$
Is velocity the gradient of position, and if so, does that make this force a conservative ...
- 65
1
vote
1
answer
90
views
Work done in sliding a block across a table, as seen in different inertial frames
Suppose, I'm pushing a block across a smooth table.
The length of the table is $d$, and the force that I applied is $F$.
According to an observer at rest, standing next to the table, the work done is $...
- 493
0
votes
2
answers
434
views
Kinetic energy constant, but net Work done is not $0$
Suppose I have two objects of equal mass and volume, in space, in contact with one another.
The two objects exert equal and opposite gravitational force on each other. Let us apply a force $F$ on one ...
- 493
2
votes
2
answers
282
views
Work done on an object whilst lifting it
Imagine to lift an object with mass $m$ from height $h_1$ to height $h_2$ and neglect the friction with air. How much work have you done on the object?
My answers (big doubt in the second one!):
...
- 1,319
1
vote
1
answer
340
views
Can average power be non zero, but instantaneous power be zero
Q. A wind-powered generator converts wind energy into electric energy, Assume that the generator converts a fixed fraction of wind energy intercepted by its blades into electrical energy. For wind ...
- 125
0
votes
4
answers
163
views
Definition of Power
I wanted to clear my doubts regarding the true definition of power. Imagine a mass falling from a height and reaching the ground thanks to gravity. The power of this event would be the work done by ...
- 161
0
votes
1
answer
34
views
Does this vector need to be fixed for the kinetic energy to be constant?
I was solving the following homework problem:
A force $\vec{F} = \vec{k} \times \vec{v}$ is applied to a particle of mass $m$. Here $\vec{k}$ is a fixed vector and $\vec{v}$ is the velocity of the ...
- 207
1
vote
1
answer
40
views
Conceptual question about rotational and translational kinectic energy
My real life problem is to calculate initial translational and angular velocities of a vehicle in a loss of control to a stop (the vehicle will translate and rotate about it's center of mass.)
Initial ...
- 111
0
votes
1
answer
258
views
Is impulse functionally equivalent to work and therefore expressible in Joules?
I am trying to understand things at at a fundamental and conceptual level.
Givens...
1 kg mass
Mass is at rest (relatively, of course)
Mass is on an idealized frictionless surface
1 N of force is ...
- 161
2
votes
2
answers
775
views
How does the work-energy theorem relate to the first law of thermodynamics?
The work energy theorem states that the net work on a particle is equal to the change in the kinetic energy of the particle:
$$W_{net}=\Delta K $$
My first question is whether this formula (the work-...
- 1,581