# Tagged Questions

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

46 views

### Work done relation to potential energy

I know work done is negative of change in potential energy, I.e., $W=-(∆U)$. It means that Work done against a force (or work done on a system) increases its potential energy. And Work done by a ...
46 views

### Work done by the system

I have a trouble in understanding the concept of the work. In the closed system, Work done by system=Work on surroundings Here is the part of the process that prove "Work on surroundings=pressure of ...
62 views

### Conventions and realities of kinetic energy?

I am having doubts regarding why $1/2$ is present in kinetic energy and if this is conventional why cant we say potential energy is $2mgh$ and kinetic energy $mv^2$. So is this $1/2$ conventional or ...
28 views

### Conservation of Energy with Rotation Caused by Friction

A book that I am using to study poses the following problem: Suppose you wish to use a spring with a force constant $k$ to launch a spherical ball or radius $r$ and mass $m$ up a ramp of inclination ...
39 views

### Principle of Maximum Work for Different Paths

The principle of maximum work states that for any process between two states, the work done by the system is maximised for a reversible process (and heat transfer is minimised), and that the work done ...
66 views

### Understanding work with rotational momentum/moment of inertia

Apologies for the basic question but between the vectors and the spinning, I'm getting confused. If I have a wheel with moment of inertia $I$ spinning at some rate $\vec\omega$ around an axis, what ...
28 views

### Electric potential and work

A unit positive charge $q$ is placed in an electric field caused due to a positive charge $Q$. $q$ experiences force of repulsion $F_R$. We apply an external force (FEXT) opposite to $F_R$. The test ...
43 views

### Work done by a force

What is the difference between work done by a force and work done against that force? Is it true that work by a force = -(work against that force)?
20 views

when we bring a unit positive charge from infinity to a point in the electric field EF does work on the charge and external work is also done on the charge in same amount but in opposite sign. then ...
32 views

### The effects of heat and work on a system

I am unable to grasp the following statements which I found in the literature. For a closed system (no transfer of matter), heat in statistical mechanics is the energy transfer associated with a ...
45 views

### Change of energy into friction?

If I am pushing a car and it does not move, I am doing no mechanical work. However, I am changing the energy that was stored in my cells into heat energy (maybe sound energy if my hand slips off the ...
22 views

63 views

### What is difference between variations of the work and virtual work?

I really want to know whether or not both equations are the same mathematically. I think that they are the same, I just want to be sure. (Reference: this website.)
21 views

### Kinetic energy vs Kinetic Energy scenario in a collision, mechanical energy used for work?

Most collisions have Kinetic energy conserved or in the case of inelastic collisions energy is lost into other forms. Though the equation of "TMEi + Wnc =TMEf" is true however, what if two unequal ...
77 views

### Is work only a change of kinetic or potential energy?

I find out on the internet that work is a transfer of energy essentially kinetic. What is the use of work if it does not consider all the types of energy applied , i mean sometimes an objects internal ...
36 views

### work done in observer frame

I had a few questions. 1) Is work done independent of the refrance frame? 2) Suppose a cart-A with rough surface is accelerating with an acceleration a and another cart-B with acceleration b. Now to ...
105 views

### Why is no work done by magnetic forces in a uniform B and E field (perpendicular to one another)?

Say $B$ points in the $x$ direction, and $E$ points in the $z$ direction. Assuming a charged particle begins at rest at the origin, its motion will be a cycloid that progresses indefinitely in the $y$...
131 views

### Is work done on a fluid in a communicating vessel necessarily equal to work done by the fluid inside it?

During the explanation of Pascal's law the argument that work done by a force to move the fluid inside communicating vessel is equal to the work done by the fluid at the other end of the vessel was ...
155 views

### Restrained expansion of a piston/cylinder

Suppose an ideal gas in a piston cylinder has some initial pressure $p_1$, volume $V_1$, and temperature $T_1$. A pin, which holds the piston in place, is suddenly removed, and the gas quickly ...
161 views

### How to solve state parameters using these givens for an ideal gas?

In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
126 views

### Problem in average height

Let, diameter of cylinder hole of height 30m and diameter 2m filled with water. In a book, when author tried to find out the power for lifting all of the water then he used average height. why is ...
31 views

### Mistake calculating electrostatic potential energy formula!

I have a problem calculating the electrostatic potential energy. I rely on these equations coming from mechanics: U_{B}-U_{A} = -W_{A \ \rightarrow \ B} (done\ by \ the \ field \ ...
28 views

### Resources on how to estimate the power density of gravity?

If a drop a ball from a height $h$, the work done by gravity (in this particular situation $i$) is $w_i=\int_0^h F_G \cdot dl \approx mgh$. What I would like, is to estimate the work done by gravity ...
55 views

### Potential Energy = mgh. What is the name of this principle and did Newton discover it?

Somebody I know keeps trying to convince me that Potential Energy $PE=mgh$ is one of Newton's Laws (as well as the closely related idea, Work Done = force x distance moved). I am fairly certain that ...
38 views

### Joule's “Work-Heat Equivalent” Experiment

I have been reading about the Joule's experiment that is supposed to have shown that work is the equivalent of heat. I can't really find the original paper and I am finding trouble understanding how ...
16 views

### Calculating the amount of work done for a bench press movement? Is this a reasonable conclusion?

Me and a friend have been working out for some time and have been bench pressing each weak, increasing our weight. Once we started getting to heavier weight we noticed that he was able to get more ...
41 views

### Magnetic force on an iron nail

Work done by a magnetic force is zero but the why iron nails are attracted towards a magnet. The fly towards a magnet so the gain K>E i.e work has been done on them. I know its not actually the ...
30 views

### Efficiency of a Carnot refrigerator without knowledge of the temperatures

We know that in a Carnot refrigerator we can express the efficiency as $$\eta = \dfrac{Q_1}{Q_2-Q_1}=\dfrac{T_1}{T_2-T_1},$$ where $T_1$ and $T_2$ are temperatures of the reservoirs between which ...
30 views

### Microscopic Definition of Heat and Work

If I am given a statistical System, then I can define state-variables like Energy, Entropy or other Observables, and then I can (at least for equilibrium states) give the Change of Energy as: \begin{...
33 views

### Why changes in the degrees of freedom implies changes in the internal energy?

In Thermodynamics we describe equilibrium states of macroscopic systems. For those equilibrium states we make a description giving one macroscopic coordinate for each measured degree of freedom (like ...
27 views

### Work + heat absorbed in a thermodynamic process

The question describes a simple isobaric closed cycle. The temperature is on the y-axis and volume on the other. There are 4 states. The question asks: ''Find the work done on the gas in the cycle and ...
22 views

### Will Energy and Work equal to each other between two closed systems linked by one shareable object?

Two closed systems are linked to each other. Both use same object. In one of this closed systems was spent energy to change physical property of shareable object. After this object transformation, ...
49 views

### The relation between work and time

Work equals the force acting on an object times the distance that object moves. But I am a bit confused about the definition of the distance. is it the distance the object moves under the effect of ...
40 views

### In terms of work, what happens to a negatively charged particle circling around a positively charged rod?

Picture a positively charged glass rod from its end so that if you were to draw it on paper, it would appear as a circle. Now, suppose a negatively charged particle moves in a circular arc, on the ...
56 views

### Electrostatic energy of a distribution of charges

I read, in Gettys' Physics, that, if $N$ charges moves one by one from infinity to a certain point, i.e. the first charge $q_1$ moves from infinity to the arrival point $P$ while the other charges ...
147 views

### Ericsson cycle: what happens if you add more mass?

We recreated the Ericsson cycle using a heat engine apparatus, with air as the working fluid (assumed an ideal gas). During the isothermal compression and isobaric expansion processes, a mass of ...
77 views

### difference between reversible and irreversible entropy

Before I proceed, let me first say I have done research and understand the general idea between the two: summed up crudely reversible happens in a slower continuous manner while irreversible happens ...
56 views

### Does Light have Weight?

If I light a torch and hold it against a wall, will the wall feel any force? If yes, what factors does the magnitude of such a force depend upon? (Area of the wall covered by the beam, intensity of ...
105 views

### How to tell direction of work

I think of direction of work as relative to direction of motion, but I got a question of a parabolic ball throw asking the direction work done by gravity and friction over the entire parabola. Since ...
121 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 ...
79 views

### Work done on an object from different frames

Consider this situation: A car is moving on a road and applies brakes. The road exerts a force $F$ on the car, due to which the car stops in $S$ meters. Clearly, the work done by the road on the car ...
534 views

### Work done by rolling vs skidding friction force

Two identical bicycles having equal weight riders are traveling along a level road adjacent to each other with the same non-zero velocity. Bike A, (the "skidder"), applies the rear brake strongly ...
185 views

### Collision of two deformable bodies - limitation of work-energy theorem

I am attempting to model the impact of a deformable body (clean, dry sand characterized as a continuous fluid) with flexible diaphragm (in this case a sheet of rubber). Assuming that this is a closed ...
19 views

### Efficiency of engine in the case non-boundary work done on the system

The engine efficiency is defined as $$\eta = \frac{W_{\mathrm{produced}}}{Q_{\mathrm{absorbed}}}\tag{1}$$ But suppose that, in one of the processes that takes place in the cycle of an engine that ...