The work tag has no wiki summary.
27
votes
7answers
875 views
How can Magnets be used to pick up pieces of metal when the force from a magnetic field does no work?
I learned that the force from magnetic fields does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets ...
2
votes
1answer
103 views
Is any work done when I walk?
I am trying to figure out the amount of work done when I walk X miles or for X minutes. So I got Work=Force x Distance and Force=Mass x Acceleration and Acceleration=(change in velocity)/time. I am ...
2
votes
2answers
108 views
How to reconcile the two definitions of work? (mechanical and thermodynamical)
When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$.
However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$.
I'm having trouble ...
1
vote
1answer
35 views
Adding heat to a system doesn't equal the work done by gas?
So, I answered a physics question for a class that goes as follows:
A gas in a cylinder is kept at a constant pressure of $250000\: \mathrm{Pa}$ while $300\: \mathrm{kJ}$ of heat are added to it, ...
5
votes
2answers
133 views
Conceptually, what is negative work?
I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ...
-4
votes
0answers
37 views
What formula is used to determine weight distribution using two people to lift 100 lbs over their head? [closed]
Trying to determine actual weight and force required to perform a two man deadlift of an container weighing 100lbs
0
votes
1answer
56 views
Short-duration forces
In circular motion, it is said that the centripetal force acts only for a very very short period of time, hence is able to only change the direction but not magnitude of the velocity.
Similarly in a ...
1
vote
2answers
41 views
Work on Ferromagnetic Object Due to Solenoid
I've been going through some equations and such trying to determine the work done by a solenoid on a ferromagnetic object. I have the following:
Magnetic field due to solenoid:
$\vec{B} = ...
0
votes
1answer
107 views
Work done by Static friction
Here $v1$ is relative to the block on which sphere is pure rolling but static friction isn't $0$ as of now .
In the following diagram, is work done by static friction $0$ ?, since the point of ...
1
vote
6answers
315 views
Centripetal Force Acceleration
Suppose you want to perform a uniform circular motion . Then a body performing uniform circular motion horizontally needs an acceleration $= \frac{v^2}{r}$ at each point on the circular path with ...
5
votes
1answer
176 views
First law of thermodynamics?
The first law says that the change in internal energy is equal to the work done on the system (W) minus the work done by the system (Q). However, can $Q$ be any kind of work, such as mechanical work? ...
0
votes
0answers
51 views
Work And Energy Question [closed]
$H = 3\text{ m}$,$m=2\text{ kg}$
The right side is rough.
I want to figure:
what is the coefficient of friction $\mu$?
How high and exceed the maximum return on the plane right body?
I know ...
0
votes
0answers
45 views
Work required to pull capacitor plates apart when connected to battery [closed]
For (a), I just use $F = k \frac{Q_1 Q_2}{r^2}$, then (b) $W = - \Delta U = - qE \Delta d$, correct so far? But how do I do (c)?
-6
votes
4answers
377 views
Violation of Newton's Second Law (?)
Here the big circle denotes the circular path of a stone(small circle on path) tied to a string from the centre of the circular path .
This is COMPLETELY HORIZONTAL
At an instant the velocity in ...
0
votes
0answers
42 views
What is the total work done in this problem? [closed]
A 1800 kg trick airplane is 450 m in the air. At this point the plane takes a dive
with an initial speed of
42 m/s and accelerates to 64 m/s, dropping
a total distance of 120 m.
(a) Using the ground ...
1
vote
6answers
387 views
Electrostatic Potential Energy Derivation
How is the boxed step , physically as well as mathematically justified and correct ?
Source:Wiki http://en.wikipedia.org/wiki/Electric_potential_energy
As work done = $- \Delta U $. for Conservative ...
1
vote
2answers
50 views
How is it possible to equate the internal energy at constant volume with the internal energy of an adiabatic process?
I hope my question makes sense. My problem is that, I have read through numerous textbooks that nC(cons. volume)dT = -PdV when deriving the relationship between T and V for an adiabatic process, ...
0
votes
1answer
96 views
Energy needed to lift and bring down an object
A mass of 0.5 Kg needs to be moved from point A to another point (B) which is 1 meters above point A. The time for this movement should be 0.2 seconds, then the mass is kept at position B for another ...
1
vote
5answers
122 views
Workdone in an equipotential surface is zero?
An equipotential surface is one in which all the points are at the same electric potential. If a charge is to be moved between any two points (say from point A to point B) on an equipotential surface, ...
0
votes
0answers
77 views
How to find work done due to friction [closed]
The force F=40N is applied on a 10kg block at an angle of 36 with the horizontal. The block moves a distance of 15m. If the surface is frictionless. If the coefficient of kinetic friction is 0.25, ...
1
vote
1answer
130 views
calculating work done by friction
I want to calculate the work done by friction if the length $L$ of uniform rope on the table slides off. There is friction between the cord and the table with coefficient of kinetic friction $\mu_k$.
...
2
votes
1answer
61 views
Work done by gravity on Water
Now according to me we would see change in potential energy of system and equate it to the work done by gravity.
But when we see this the first column lowers by $H/2$ and right one rises by $H/2$ ...
0
votes
1answer
35 views
Work done by complex field on complex plane
A force field is given by $F = 3z+5$. Find the work done in moving an object in this force field along the parabola $z = t^2 + it$ from $z = 0$ to $z = 4+2i$.
I don't understand why conjugate ...
0
votes
4answers
163 views
How do you tell what forces do no work?
The total mass of the children and the toboggan is 66 kg. The force the parent exerts is 58 N (18 degrees above the horizontal). What 3 forces/ components do no work on the toboggan?
I said the ...
0
votes
1answer
86 views
About the work done by gravity to pull the object down to the earth surface
The following question is from an physics exercise and I know the answer and the way to solve the problem but just curious why my own way doesn't work. The question is asking "A 2500kg space vehicle, ...
1
vote
1answer
136 views
Work done by friction
Suppose we have a block of mass $M$ and we are moving it up a curve, very slowly ($a=0$). The surface is not smooth, and coefficient of friction is $\mu=\mu_s=\mu_k$.
To move the block we apply a ...
3
votes
1answer
107 views
Intuition behind Work
I have a doubt in understanding the intuition behind the concept of work. First of all, I think this isn't duplicate, I've searched on the site, and the closest thing I've found was this post which is ...
2
votes
1answer
207 views
How to understand the work-energy theorem?
How to understand the work-energy theorem?
I took a short lecture on physics for engineering last week. The lecturer emphasized that the work done on an object will cause the kinetic energy change as ...
0
votes
1answer
72 views
Why work to change velocity from 0 to 20 km/h is less then from 20 to 40? [duplicate]
Imagine spaceship in vacuum with mass = 1. At beginning, it has velocity 0, and kinetic energy 0.
$$W_1 = 0$$
Then, it turns on its engine, and changes velocity from 0 to 20 (delta v = 20). It's ...
1
vote
1answer
81 views
Work as an integral of mass over velocity?
As I've understood it, the area under $F$-$s$-graph is the work done, so then :$$W(s)=\int{F(s)ds}$$
I am also given this equation ($W_k$ is kinetic energy, which is equal the work done to set the ...
1
vote
3answers
177 views
Integration by parts to derive relativistic kinetic energy
I have come across a weird integration during derivation of relativistic kinetic energy. Our professor states that i can get RHS out of LHS using integration by parts:
$$
\int\limits_0^x \! ...
1
vote
0answers
43 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 ...
0
votes
0answers
49 views
Work, energy and friction [closed]
A car loaded with bricks has a total mass of 18kg and is pulled at a constant speed by a rope. the rope is inclined 30 degrees with above the horizontal, and the cart moves 20.0 m on a horizontal ...
0
votes
0answers
28 views
How did scientists come up with Work? What was it fundamentally defined as? [duplicate]
Now before I get into the questions I want to make a couple of things clear, I know that there were similar questions like this and I've been through (what i think is) all of them and none of the ...
1
vote
2answers
163 views
Finding maximum speed in a work-energy problem
I have the following problem:
The Royal Gorge bridge over the Arkansas River is $310\text{ m}$ above
the river. A $57\text{ kg}$ bungee jumper has an elastic cord with an
unstressed length of ...
1
vote
0answers
45 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 ...
3
votes
2answers
123 views
Find work done by force along a path - is parameterization the only way?
$F = x^3y^4 \hat i + x^4y^3 \hat j$ from $(0,0)$ to $(1,1)$.
I am given different paths.
For example, "first along x axis and then along the y axis" is one of the paths.
Is this problem solvable ...
3
votes
3answers
122 views
When can one write $a=v \cdot dv/dx$?
Referring to unidimensional motion, it is obvious that it doesn't always make sense to write the speed as a function of position. Seems to me that this is a necessary condition to derive formulas ...
4
votes
2answers
123 views
Conservative Force and $1/r^2$
Does the inverse square law have anything to do with conservative behavior of the central forces?
1
vote
2answers
82 views
How can I understand work conceptually?
I'm in a mechanical physics class, and I'm having a hard time understanding what the quantity of work represents. How can I understand it conceptually?
1
vote
1answer
173 views
Work done in projectile motion
A projectile is shot at some inclination to the ground. It falls at another point having R distance from the initial point on the ground. Is there any work done?
If initial velocity vector is $(u\cos ...
3
votes
4answers
585 views
Why does an object thrown parallel to the ground eventually fall down?
Suppose an object is thrown parallel to the ground. The gravity acts downward (ie. perpendicular to the direction of motion of the object). The work done by gravity on that object will be given by :
...
1
vote
3answers
627 views
What is $vdp$ work and when do I use it?
I am a little confused, from the first law of thermodynamics (energy conservation)
$$\Delta E = \delta Q - \delta W $$
If the amount of work done is a volume expansion of a gas in, say a piston ...
0
votes
2answers
129 views
Measuring work done by gravity over non-constant gravitational acceleration
A question from an example from a MIT Classical Mechanics Lecture on Work.
Here's the given definition for gravitational potential energy (~32:00): "The ...
8
votes
3answers
603 views
Is the normal force a conservative force?
Most of the time the normal force doesn't do any work because it's perpendicular to the direction of motion but if it does do work, would it be conservative or non-conservative?
For example, consider ...
-1
votes
2answers
411 views
Work done by the air resistance [closed]
A ball of mass 0.37 kg is thrown upward along the vertical with a
initial speed of 14 m / s, and reaches a maximum height of 8.4 m.
a) What is the work done by air resistance on the ball? b) ...
1
vote
3answers
141 views
Can endergonic reactions occur outside of living organisms?
If the Gibbs free energy equation is defined as:
∆G = ∆H - T∆S
And the amount of energy/work released from a reaction is:
...
0
votes
1answer
139 views
Is resistance to motion directly proportional to the speed of a moving object?
Power is known to be equal to the force x velocity (P=FV).
Im solving a question that states the following :
Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s ...
2
votes
1answer
62 views
Conservative forces intuition
Take a gravitational field (with all the field lines pointing inwards) and a perfectly circular curve as an object's trajectory. To find the work exerted by the force on the object, compute the line ...
1
vote
2answers
197 views
Mechanics Question: Energy, Work and Power
I'm a pure mathematician by trade, and have been trying to teach myself A-level mechanics. (This is not homework, it is purely self-study.)
I've been working through the exercises and have come up ...
