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16

Work is calculated as force times distance. $$W = Fd$$ The purpose of a simple machine like a screw jack is to lessen the force required. However, the work needed is still the same, so the distance over which you exert the force has to increase. Halving the force requires doubling the distance. In this problem, you want to lift 2000 lbs a distance of 1 ...


6

How can the work energy theorem be valid in presence of non-conservative forces since conservation of energy is not there? The work-energy principle simply states that work is the net increase of KE The principle of work and kinetic energy (also known as the work-energy principle) states that the work done by all forces acting on a particle ...


5

From the geometry, you can state that in order to move the screw by 1 unit of distance, you have to move the end of the handle by $10\times 20\times 2\pi$ units of distance. Let's call the unit of distance $[L]$ - in this case, an inch might be a good unit but we don't have to be explicit about that. Conservation of energy says that work done on the system ...


3

When you stretch a rubber band there is considerable deformation to the polymer molecules in the rubber. As a result some of the work you do on the rubber band goes into exciting molecular vibrations i.e. heat. Some of the work you do is stored as elastic energy and some is dissipated as heat. As the band is allowed to relax the elastic energy stored within ...


2

Mechanical energy is not conserved since friction acts on the system. Also recall that the displacement done by the object down the inclined plane is not the difference in height. The answer shown comes from an analysis of the forces that are involved in the movement of the object. Draw a body-diagram and you will get $mg(\mu_k \cos \theta - \sin \theta)$ ...


2

The only factor is the capacity to return to the original shape when it is deformed by an external force. An elastic object recovers its shape after it has been compressed and deformed, if you crush a plastic bottle and remove the cap it will partially return to his original length, a lead ball is almost completely irreversibly deformed. The Coefficient ...


2

The Fundamental Theorem of Calculus is of course correct, and you are applying it correctly. The statements the rate of change of work with respect to displacement is force and the instantaneous rate of change of work with respect to displacement is force are correct. The thing to keep in mind is that it's not work that is instantaneous, but its ...


1

if we want to move a charge in an electric field then we need a work of an external force to move it from a low potential energy to a high one Not true. The electric field itself exerts a force to move the charge. Moving the charge from high to low does require work and this work is done by the electric field itself. Any force that causes movement is ...


1

When you extend the rubber band, you store potential energy in it. Now when you release the rubber band this potential energy is converted into kinetic energy (the ends of the rubber band start moving). In an ideal situation the energy of the rubber band would then stay constant, (potential would convert to kinetic energy and then kinetic would convert to ...


1

The other answers are great. I decided to plot it, however, because it's nice visualizing these things. Since your biggest doubt is about kinetic energy, be sure to pay attention to the last graph. SYSTEM. Motorcycle going to the left, truck going to the right, bound by an elastic rope ten meters long ($k=100\frac{\mathrm N}{\mathrm m}$). Masses and speeds ...


1

No matter how ridiculous you may find it, it is true. The most general definition of work is indeed that the infinitesimal work done along an infinitesimal path is just force times the length of the path, i.e. $$ \mathrm{d}W = F\mathrm{d}s$$ Therefore, the amount of work done along a path in space $\gamma : [a,b] \to \mathbb{R}^3$ is the line integral $$ ...


1

What I assume the book is trying to say is that, as the electrons move downward (because they are part of a current), the magnetic field bends their path toward the left. This is the horizontal motion that the book mentioned. But of course the electrons can't run off the edge of the bar, so they pile up at the left side, leaving unmatched positive charges ...


1

No, while the work the engine does would be reduced by a tailwind, it would not be reduced to be equivalent to the relative speed travel. Work $\ne$ Force The work that the engine must exert to maintain speed is equal to the drag times the velocity. So let's look at the ideal situation where the only drag on the car was due to the wind. The drag on a car ...


1

There are several possibilities for your confusion - and you bring up several related concepts (Work, potential energy, kinetic energy). When this happens I think it's helpful to isolate one thing which you know must, absolutely be true. The definition of work (for a constant force) is $$W=\vec{F}\cdot \Delta \vec{x}=F\Delta x \cos\theta.$$ First ask "what ...


1

Derivation that applied work as defined above results, for a particle moving along a straight line, in a change in its kinetic energy (I hope it is not too complex to understand): In the case the resultant force $F$ is constant in both magnitude and direction, and parallel to the velocity of the particle, the particle is moving with constant acceleration a ...


1

Sometimes when you're stuck on things, it's helpful to look at the mathematics of what's being asserted. For example, nowhere in Newton's three laws does "energy is conserved" appear. Energy conservation does appear, however, when you have a system that behaves like $m \ddot{x}=-\nabla U$, for some function $U$, where $x$ is a position vector as a function ...


1

The vertical component of the force doesnt do work, so a force with an obtuse angle can be considered to be oppossed to the diplacement. In any case, whenever work is negative, the system is losing energy.


1

You can calculate the work done by gravitational force as the product of its weight and y-displacement. If I have got your question right, the body is freely falling after the force tips it off the table. So the work done by your force will not be as you have written. It would've been correct if the force had been acting on the body throughout its ...


1

It is the electric field that does the work, not the magnetic field! When one has current in the loop, it can undergo a voltage drop or rise according to the inductance of the coil. Inductance relates to the electric field and its work. See: http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction "The induced electromotive force in any closed circuit ...


1

Well first off, I think you forgot that $S$ was the displacement along the incline. The object will slide down from $y=h$ to $y=h-(S\sin(\theta))$ (change in vertical displacement). The only work done here is by friction and by gravity. We know gravity is doing positive work and that friction is doing negative work. The work done by friction is simply ...



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