The work tag has no wiki summary.
3
votes
1answer
422 views
Area under a $pV$ diagram
What does the area under a Pressure volume diagram equal?
I read in my textbook it equals 'external' work done, but why is this?
First of all, what exactly is external work?
Can you get it ...
2
votes
1answer
100 views
Moving along friction surfaces
If a particle moves along a one dimensional surface with constant friction. As the particle moves from point $A$ to point $B$ it loses an amount of energy equals $E(A,B)$. Consider that the particle ...
1
vote
2answers
304 views
Calculating force required to stop bungee jumper
Given that:
bungee jumper weighs 700N
jumps off from a height of 36m
needs to stop safely at 32m (4m above ground)
unstretched length of bungee cord is 25m
Whats the force required to stop the ...
0
votes
0answers
52 views
Need help with physics [closed]
The net force along the linear path of a particle of mass 320g has been measured at 13.0cm interval, starting at x=0.0, to be 26.0, 28.4, 28.8, 29.6, 32.4, 40.1, 46.6, 42.2, 48.8, 55.7, 55.8, 60.2, ...
1
vote
1answer
388 views
Needed Energy For Lifting 200 kg weight
I'd like to learn how much energy I need to lift a 200 kilograms weight on normal earth conditions?
For example how much electric power do we need?
I'm not a physicist and not a student and this ...
0
votes
3answers
247 views
A chain 64 meters long whose mass is 20 kilograms is hanging [closed]
A chain 64 meters long whose mass is 20 kilograms is hanging over the edge of a tall building and does not touch the ground. How much work is required to lift the top 3 meters of the chain to the top ...
0
votes
0answers
141 views
Air condition and net heat [closed]
I have attempted to solve a problem, but my answer is not quite the same as in the book. Thus, I would really appreciate it if someone could confirm/disconfirm whether or not my solution is correct.
...
1
vote
1answer
261 views
ratio between work and heat [closed]
I am really stuck on a problem in my textbook:
Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
1
vote
2answers
871 views
Thermodynamics - Sign convention
I use the sign convention:
Heat absorbed by the system = $q+$ (positive)
Heat evolved by the system = $q-$ (negative)
Work done on the system = $w +$ (positive)
Work done by the system = $w -$ ...
1
vote
2answers
227 views
Why is work defined as force dot displacement?
Why is work defined as force dot displacement? I know that it is defined like that based on the observational fact - we do more work when we apply greater force or move to a greater distance. But I ...
0
votes
1answer
215 views
Energy used to stop / slow an object
I'm trying to workout how much energy (if any), I use (imagining me as an efficient machine rather than a complex bio-mechanical human) when I lower or catch a weight. I understand that when I push it ...
0
votes
1answer
1k views
How much work is needed to compress a certain volume of gas?
I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
0
votes
1answer
130 views
Power, Force Velocity
In any case, if the force and power is constant , does velocity also need to be constant? If no, can you tell me a case.
Further can this be extended for non-rigid bodies.
4
votes
5answers
2k views
Why there is a 1/2 in kinetic energy formula? [duplicate]
Possible Duplicate:
Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?
Hèllo, I have a question about kinetic energy formula.
As you know, in kinetic energy formula, we have:
...
1
vote
0answers
79 views
How would a physicist move? [closed]
Let's assume that Johnny Physicist has decided to move from his poor dingy second story apartment, into his much deserved home. Without making modifications to the existing structures? What would be ...
2
votes
3answers
959 views
How do I find work done by friction over a curve represented by a polynomial?
I am facing a problem in Physics.
Problem: What will be the work done by the frictional force over a polynomial curve if a body is sliding on this polynomial($a+bx+cx^2+dx^3+\ldots$) curve from rest ...
1
vote
3answers
108 views
Carrying water on person, or on the frame when bicycling
So, the question is as follows:
What is the difference in work exerted by the rider in the two following scenarios?
a) Rider + bike. Water carried in a holder on the frame
b) Rider + bike. Water ...
3
votes
1answer
337 views
I have a slight problem understanding the concept of “work”?
What I understand is that work is not the same as a car using gas or a crane lifting a car high up into the air. Let's use the crane as an example. And let me write out a few lines from the book.
...
3
votes
3answers
171 views
Why does it require such little energy to create the fastest thing in the universe?
I have noticed when I turn on the light switch in my house light comes from the bulb.
How is this light created?(process occurring in the bulb) and why is this small amount of electricity enough to ...
3
votes
2answers
178 views
When work is performed solely by magnetism, is there an equivalent loss of energy from the magnetic field?
When two magnets are placed within appropriate proximity and released, the attractive force will perform work and bring them together. Work is performed overcoming friction. Can we measure a ...
2
votes
1answer
379 views
Does moving something horizontally in gravity do no work?
Bill’s job is to lift bags of flour and place them in the back of a
truck, which is parked next to him. Sally is loading the same bags of
flour into a similar truck that is located 10 m away. ...
1
vote
2answers
559 views
Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?
For elastic collisions of n particles, we know that momentum in the three orthogonal directions are independently conserved:$$ \frac{d}{dt}\sum\limits_i^n m_iv_{ij} =0,\quad j=1,2,3$$
From this, it ...
5
votes
5answers
1k views
Why does work equal force times distance?
My 'government-issued' book literally says:
Energy is the capacity to do work and work is the product of net force and the 1-dimensional distance it made a body travel while constantly affecting ...
2
votes
1answer
116 views
Work Done to click a mouse?
Is there any good research done to find out the work done in clicking a mouse button.
any link to that would be greatly appreciated.
P.S.
i am not too sure whether this question belongs here or ...
0
votes
1answer
69 views
System moves away from equilibrium $\rightarrow$ it has energy added?
Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium.
Between moments $[t_1, t_2)$ the isolation is violated and ...
1
vote
0answers
32 views
Is energy applied by the muscle when it holds a body in the air? [duplicate]
Possible Duplicate:
Why does holding something up cost energy while no work is being done?
We all know the following Newtonian formulas:
PotentialGravitationEnergy=m*g*h
Kinetic Energy = ...
3
votes
1answer
304 views
A Question about Virtual Work related to Newton's Third Law
In describing D'Alembert's principle, the lecture note I was provided with states that the total force $\mathbb F_l$ acting on a particle can be taken as,
$$\mathbb F_l=F_l+\sum_mf_{ml}+C_l,$$
...
1
vote
3answers
144 views
Magnetic force and work
If the magnetic force does no work on a particle with electric charge, then:
How can you influence the motion of the particle? Is there perhaps another example of the work force but do not have a ...
1
vote
1answer
306 views
Work and Area under a Curve relating to Hooke's Law
If it takes work W to stretch a Hooke’s-law spring (F = kx) a distance d from its unstressed length, determine the extra work required to stretch it an additional distance d (Hint: draw a graph and ...
2
votes
3answers
510 views
Statics software for structural engineering
I'm attempting to expand my knowledge of engineering software. I've found comsol and ansys for acoustics and thermodynamics/fluid dynamics (not necessarily in that order), now I'd like to see if I can ...
2
votes
4answers
604 views
Work done by the Magnetic Force
The magnetic part of the Lorentz force acts perpendicular to the charge's velocity, and consequently does zero work on it. Can we extrapolate this statement to say that such a nature of the force ...
2
votes
2answers
130 views
Mechanical work to required battery power
I have a very practical question where I've calculated the mechanical work needed by a simple mechanical system by solving the line integral $W = \int_C \ F \ dx$. However, since I have a black spot ...
21
votes
7answers
3k views
Why does holding something up cost energy while no work is being done?
I read the definition of work as
$$W ~=~ \vec{F} \cdot \vec{d}$$
$$\text{ Work = (Force) $\cdot$ (Distance)}.$$
If a book is there on the table, no work is done as no distance is covered. If I ...
