All Questions
30
questions
1
vote
1
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41
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Work using angle vs. displacement [closed]
I am trying to calculate the work done on this wheel as it undergoes one full revolution, and is rolling without slipping.
I am aware that work can be calculated either using the integral of force ...
- 21
2
votes
2
answers
199
views
Why is the gravitational potential energy lost not subtracted from the required work done in the given problem? [closed]
An elastic string of natural length $l \;\text{m}$ is suspended from a fixed point $O$. When a mass of $M \;\text{kg}$ is attached to the other end of the string, its extension is $\frac {l}{10} \;\...
- 175
1
vote
1
answer
341
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
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
825
views
Work done for conservative forces is path independent Proof
So I’m looking at the proof for work that is path independent.
There is a line were the integral
Partial derivative V dr from r1 to r2 becomes
Partial derivative V r’ dt from t1 to t2
I’m a bit ...
0
votes
1
answer
263
views
Taylor Example 4.8. Is my reasoning sound? [closed]
This problem has been giving me all sorts of fits. For one, Taylor states that because the frictional force and normal force are forces of constraint, they produce no work. I'm trying to figure out ...
0
votes
2
answers
122
views
Is work done by the normal reaction force when an object is dropped on the ground?
When a perfectly non elastic object (let's say a book) is dropped on the ground, it's kinetic energy from the fall is transformed into heat and sound.
Now, if W = Fs, the work done by the normal ...
- 5
1
vote
1
answer
72
views
Variable Exchange $F(t) \to F(x)$? I want the value of the work done by drag [closed]
I got a nonlinear equation, which describes the magnitude of a force as a function of time, but I don't know how to calculate the work done by the force. Given:
$$F(t) = kv(t)$$
with
$$v(t)= \left(1-\...
3
votes
2
answers
616
views
Net Work Done When Lifting an Object at a constant speed [duplicate]
I am confused about the amount of work done when lifting an object at a constant speed. If you find the work done by you on the object and the work done by gravity on the object and add them the net ...
- 43
-1
votes
1
answer
486
views
The work done by emptying a well full of water upto a certain height [closed]
Lets say we have a well full of water (For now lets say it is cylindrical) .Lets say its height is $h$$well$. The water is filled upto a height $h$$water$. The radius of the well (cylindrical) is $r$ ....
- 307
1
vote
2
answers
50
views
Calculating work done vs. calculating final energy [closed]
I'm trying to solve for work after 2 seconds given $v(t)=3t^2$ and mass$=1kg$. There are 2 approaches:
Just calculate kinetic energy after 2 seconds: $E_k=.5*mv^2 = .5 *1 * (3*2^2)^2 = .5* 144 = 72J$
...
1
vote
2
answers
380
views
Why is the work done by a block into a spring the same from the work done by the spring on the block?
In the following situation:
A 700 g block is released from rest at height h 0 above a vertical
spring with spring constant k = 400 N/m and negligible mass. The block
sticks to the spring and ...
- 503
-1
votes
1
answer
48
views
Pendulum speed at angle $\phi $, expressing $d\vec{l}$ in terms of angle [closed]
Problem statement: Pendulum swings at angle $\phi = \phi_{0}$ , and $v_{\phi_0} = 0$. We want to find the velocity when it swings at an angle $\phi$.
Attempt at problem: By work energy theorem $$ \...
- 157
2
votes
1
answer
93
views
Conservation of energy with friction on a pool ball
I have a problem where I am given the mass $m$, radius $r$ and friction $\mu$ between a pool ball and table. The ball is not initially moving but at $t=0$ is struck by an impulse
$$p=\int_{-\epsilon}^...
- 33
1
vote
3
answers
5k
views
Concept of work done by spring
While deriving work done by spring force, our main problem is we cannot take out ${\bf F}$ vector out of the integral because it is not constant.
Hence we adopt the following method-
Considering a ...
- 329
-1
votes
2
answers
111
views
How is work done on an object zero if it’s position is changed with respect to Earth? [closed]
A porter lifts a suitcase weighing 20 KG from the platform and puts it on his head 3.0m above the platform. Calculate the work done by the potter on the suitcase. -Since kinetic energy of the ...
- 153
1
vote
1
answer
1k
views
work done by static friction in different reference frames
Consider the following scenario: A mass of m is kept on a rough inclined surface of angle of inclination $\theta$. The elevator goes up with a constant velocity v and the block does not slide on the ...
- 67
0
votes
1
answer
869
views
Determining whether a force is conservative
From my understanding, most forces that are conservative are of the form
$$\vec F = \hat i F(x)$$
Which means the force is only a function of one variable, which means the work done of the force in ...
- 3,200
0
votes
1
answer
3k
views
Calculating the work done by a particle experiencing a force in polar coordinates
Above is the source of uncertainty I have in understanding the motion of this particular particle. I'm consider (a) here, and here is my thinking:
The particle's motion is hard for me to understand. ...
- 3,200
1
vote
3
answers
594
views
What is the correct way to estimate the work done by a climber?
My teacher gave us a worksheet with word problems and their solutions. It is in German, so I have tried my best to translate it to English:
A 26 year old man climbs Mount Everest (8848 m) in only 8 ...
- 19
0
votes
3
answers
129
views
Do I apply any force towards right when I move an object towards right through air (neglecting air friction)?
I am holding an object in my hand fully extended in air. If I move it towards right , will I have to apply any force in the direction of motion (neglecting air friction)?
In my book they say work ...
- 571
-2
votes
1
answer
99
views
basic question about work exercise [closed]
I am learning independently from Tobochnik's statistical physics text.
He asks a warm up question about work:
A person pushes a block up a frictionless ramp. Is the work positive, negative, or ...
0
votes
1
answer
137
views
How do I calculate the work done on standing an object upright?
So I was trying to figure out how much work someone does when they do a sittup or crunch. I guess to make things simple, I'm imagining a really really thin rod with some uniform mass lying on the ...
- 101
4
votes
2
answers
599
views
Work done changes between reference frames?
(This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent ...
- 43
1
vote
2
answers
1k
views
Work done by reaction forces between objects
Assume that there are no friction forces. If we had a particle sliding down a wedge that is free to move on a smooth surface, why do we ignore the work done by the reaction forces on both the particle ...
- 85
1
vote
2
answers
987
views
Understanding a graph of energy conservation with bounded and unbounded motions?
This graph is from the physics undergraduate text "Classical Mechanics by Douglas Gregory".
Above this graph was the statement:
What I didn't understand is- as stated in the under [*paragraph], won'...
- 75
4
votes
2
answers
488
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 ...
- 679
-1
votes
1
answer
484
views
Can someone explain the solution (provided) of this conical pendulum work problem [closed]
In the image, it looks like the tangential direction is always 45 degrees away from the string, not 90 degrees. Is it not the circular path that the solution is talking about?
- 111
1
vote
1
answer
2k
views
Solve a problem of work and energy
A man pulling sled of his daughter by a massless rope, climbing a snowy hill whose slope is equal to 15 °. Considering that the mass of the sled is $4Kg$, the girl's $26Kg$ and $\mu _c = 0,25$, ...
- 113
0
votes
4
answers
6k
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 ...
