Conservation of energy Definition and 1000 Threads

Let $u\in\mathcal C^1(\overline R)\cap \mathcal C^2(R)$ where $R=(0,1)\times(0,\infty).$ Suppose that $u(x,t)$ verifies the following wave equation $u_{tt}=K^2 u_{xx}+h(x,t,u)$ where $K>0$ and $h$ is a constant function. a) Determine the total energy of the string. (Well I don't know what does...

My text was able to show that for an ideal (incompressible and inviscid) and steady fluid in a gravitational field, the energy density E=\frac{1}{2}\rho u^2 + \rho\chi+P is constant for any fluid element, where \chi is the gravitational potential. That is \frac{DE}{Dt}=\frac{\partial...

Hi PF! I was wondering, if the holographic principle (from string theory) really can be true. I see some physical flaws in the way it works. Here is why: Suppose that the second law of thermodynamics is true. It states that for any system, the multiplicity of the system must increase, ergo...

Homework Statement The problem relates to a water tank see link http://www.phys.unsw.edu.au/~jw/1131/IntroLS.pdf and scoll down a little! Homework Equations The Attempt at a Solution so I think to go about this problem I need to use a conservation of energy approach. ie ke(i)...

I am a TA for a physics teacher. I wrote a problem that the students did in the lab quiz. The students tried to use conservation of energy instead of conservation of charge, which I used. Both methods seem sound to me, but they produce different answers. I need help figuring out which method is...

Homework Statement A spring is attached to two blocks. The smaller block is 4.0 kg and the larger block is 8.0 kg. Initially the spring is in equilibrium and the blocks are separated by a d = 25 cm. The spring constant k = 400 N/m. No friction is present. I now push on the two blocks...

Homework Statement A train with a mass of 250 tonnes starts from rest and accelerates up an incline of 1 in 100 attaining a speed of 45 Kph after traveling 200m. If the frictional resistance to motion is constant at 30KN calculate the work done by the engine using the principle of conservation...

Homework Statement Drew kicks a ball (mass=0.250 kg) off his back porch at h= 1.50 m above the ground with an initial speed v= 17.0 m/s at some known angle. Find the initial kinetic energy of the ball. Find the initial potential energy of the ball. Find the kinetic energy and the speed v...

I am assuming the answer to my question is no, but what am I missing? My reasoning is very basic: E=hf, therefore as the universe expands the wavelength of all the far traveling radiation is increased and due to constant velocity c their frequency must decrease which translates into them losing...

Conservation of energy ? Homework Statement I was trying to solve this question " A mass M , attached to a horizontal spring , executes SHM with Amplitude A1 , when the mass M passes through its mean position then a smaller mass m is placed over it and both of them move together with...

One thing that always puzzled me was that to me, magnets seem to violate the law of conservation of energy. They obviously do not, and it is purely my ignorance that is allowing me to think this, but I need some explanation as to why they don't. What I mean by this is the following.. Say...

Can someone explain this please. From what I understand momentum is often the more fundamental as it is spatially invariant, whereas energy is time invariant and as more real world cases fall into the former category momentum is often more fundamental. What is meant by spatial invariance...

Homework Statement The mixing tank shown here initially contains 50 kg of water at 25°C. Suddenly the two valves and the single outlet valve are opened so that two water streams, each with a flow rate of 5 kg/min, flow into the tank, and a single exit stream with a flow rate of 10 kg/min...

Pam has a mass of 47.1 kg and she is at rest on smooth, level, frictionless ice. Pam straps on a rocket pack. The rocket supplies a constant force for 15.3 m and Pam acquires a speed of 59.2 m/s. What is the magnitude of the force? Answer in units of N The acceleration of gravity is...

Homework Statement An electron is released from rest on the axis of a uniform positively charged ring, 0.174 m from the ring's center. If the linear charge density of the ring is +0.150 nC/ m and the radius of the ring is 0.348 m, how fast will the electron be moving when it reaches the center...

Hi I am trying to understand the effect of dropping a magnet through a single coil of wire. If there is one turn of wire, connected to a resistor, and a magnet with known mass and flux density is dropped vertically through the coil, a current will be induced in the coil. The forces acting...

Fritz Strobl thrilled the world when he won the gold medal in the Salt Lake City games of 2002 in a daring run down an alpine skiing course. The course had a vertical drop of 880 meters. Assume his highest speed was 140 km/h, and that he was moving at that speed at the end. (a) How fast would he...

A child on a swing pumps hard and achieves a speed of 6.7 m/s at the swing’s lowest point. She then stops pumping. How high above the lowest point does the swing reach after that? I honestly have no idea how to go about solving this. I know the velocity is 6.7 m/s (but is it final or initial or...

Help me rationalize "conservation of energy" So, I understand conservation of energy, but...I must be missing something, because in my mind, there are some problems with it. Let me explain by using an example. I'm sure you'll set me straight. Okay, let's say that I have a bow and arrow. I...

Mwater g(H+h) If you have a column of water 100 meters tall (10 atm) and you insert an object in at the bottom of the column you have to use enough energy to displace the volume of the object. The pressure times the volume is your energy requirement: correct? But suppose you were able to...

Homework Statement A ball of mass M and radius R has a moment of inertia of I =2/5MR. The ball is released from rest and rolls down the ramp with no frictional loss of energy. The ball is projected vertically upward o a ramp as shown in the diagram, reaching a maximum height ymax above the...

Homework Statement A solid 162 N ball with a radius of 0.350m rolls 5.9 m down a ramp tha is linclined at 33° with the horizontal. If teh ball starts from rest at the top of the ramp what is the angular speed of the ball at the bottom of the ramp? Homework Equations MEi= MEf PEg=KE +...

Homework Statement Your favourite physics teacher who is late for class attempts to swing from the roof of a 24-m high building to the bottom of an identical building using a 24m rope as shown in Figure 5. She starts from rest with the rope horizontal, but the rope will break if the tension...

Things with a magnetic field constantly shed light. This is why a precessing magnet will slow down until it stands straight up, giving it the lowest potential energy. But if the magnet is standing straight up, it has no way to have less potential energy, but I would think that it would continue...

I have noticed that I try to apply conservation of energy laws to solve various problems, and they don't always work. For example, this problem I'm doing now is a roll of toilet paper that drops to the floor while someone is holding the first sheet of paper. Is it the presence of a tension...

Homework Statement Homework Equations K.E = 1/2(m)(v final)^2 P.E = mgh 1/2k(x)^2 <--I don't understand how you would know to use this one The Attempt at a Solution Ok so I said that energy would be conserved so E initial would equal E final. This is what I did to...

I'm doing my physics homework and for one of the questions i have to find m(mass) when i already know Ek(kinetic energy) and v(velocity) with the equation Ek=(1/2)mv^2. I was just wondering if someone could tell me how to move the m in front of the equal sign and to move Ek to the other side.

I'm pretty sure I understand everything my book says about force and mechanical energy for point particles. I'm slightly confused about how this applies to systems of particles. For particles: The line integral of force over a path is the change in KE. For conservative fields you can set a...

wrong forum

A pinball (solid sphere of mass=0.2 kg, outer radius=0.3 m) is cocked back 0.7 m on a spring (k= 50 N/m), and fired onto the pinball machine surface, which is tilted. c) When the pinball is 2.5 m above its initial location (on the way up), find its linear and angular speeds. I got...

Homework Statement 1. Consider a rod of mass 1g and length L, held in place against a vertical wall by a cable at the opposite end as shown in the diagram. A sign of mass 10kg is also hanging o the end of the rod furthest from the wall. The angles marked are 30 degrees and 45 degrees . (a)...

The problem is as follows: Two long coaxial cylindrical metal tubes (inner radius a, outer radius b) stand vertically in a tank of dielectric oil (susceptibility χe, density ρ). The inner one is maintained a potential V, and the outer one is grounded. To what height (h) does the oil rise in the...

I have a closed system (a wind tunnel with entrained air) where a high speed air flow sucks up ambient air to provide a combined flow of the 2 air streams over the model. The resulant flow has a mass flow rate equal to the combination of the 2 air streams. However in calculating the velocity...

Homework Statement A 2.0 kg load has an initial velocity of 0.65m/s. If a frictional force acts to slow it down, how fast is it sliding down the inclined plane just before it reaches the ground? The coefficient of friction between the load and the inclined is 0.30. Given/Known Data: M...

Homework Statement Here is the question I am having issues with... Below are my questions regarding it. Homework Equations The Attempt at a Solution Now when looking at this, first I would assume I use conservation of momentum. (K + Ug + Us)i = (K + Ug + Us)f + Ff d...

Homework Statement A bungee jumper of mass 64.5 kg (including safety gear) is standing on a platform 48.0 m above a river. The length of the unstretched bungee cord is 10.1 m. The force constant of the cord is 65.5 N/m. The jumper falls from rest and just touches the water at a speed of...

In my calculus bases physics 1 class our teacher assigned us a 4-5 page paper on conservation of energy. He said to talk about a specific topic of our choosing that had to do with conservation of energy. I'm an astronomy/mathematics major, and I was hoping somebody could help me decide on a...

Homework Statement Homework Equations total initial energy = total final energy The Attempt at a Solution what i got (i) 33.55J (ii) 98.1J (iii) 27.66J I am unable to obtain (iv). having block B in mid air and i have no height given to me, I cannot input any height for my...

Homework Statement use conservation of energy to derive a formula for the speed of a car in terms of energy it has at the start. you have to use energy and height as the two variables Homework Equations The Attempt at a Solution i think it is kenetic energy x mgh

Homework Statement A roller coaster travels on a frictionless track as shown in the figure. (a) If the speed of the roller coaster at Point A is 5.0 m/s, what is its speed at Point B? (b) Will it reach Point C? (c) What speed at Point A is required for the roller coaster to reach Point...

Homework Statement A 12.9 kg case of bottled water is released from rest down a shipping ramp inclined 27.2° to the horizontal. At the base of the ramp, oriented parallel to its surface, is a spring that can be compressed 2.12 cm by a force of 280 N. The case of water moves down the ramp and...

Conservation of Energy- A Skier on a Snowball Homework Statement A skier of mass "m" starts at the top of a very large frictionless hemispherical snowball of radius "r" with a very small initial speed and skis straight down the side. Treat the skier as a point particle. a) At what angle...

Homework Statement Consider two masses of 3.3 kg and 7.4 kg connected by a string passing over a pulley having a moment of inertia 12 g · m2 about its axis of rotation, as in the figure below. The string does not slip on the pulley, and the system is released from rest. The radius of the...

Homework Statement A 2.70kg mass is pushed against a horizontal spring of force constant 25.0 N/cm on a frictionless air table. The spring is attached to the tabletop, and the mass is not attached to the spring. When the spring has been compressed enough to store 12.0 J of potential energy...

Okay so I think the answer should be 180N/m unless the book is wrong and I got 114N/m. Now if there is a mistake in my work shown in the picture it would have to be the height final or height initial. I am going with height inital is the x initial and the height final equals the x final.(I think...

The question is shown below the --- or this question and answerbook is from U Physics 12E #7.71. I uploaded a JPG that can be seen at http://i43.tinypic.com/35j9jja.jpg I don't understand this problem. I see that to solve this Conservation of Energy and N2L are merged using x, and that h from...

Homework Statement Two boxes are attached to opposite ends of a rope passing over a frictionless pulley as shown below. The mass of Box A is 15kg and the mass of box B is 12kg. The system is originally at rest with the bottom of box A at a height of o.85m above the floor. When the system is...

Homework Statement Tarzan, who weighs 688 N, swings from a cliff at the end of a convenient vine that is 23.0 m long . From the top of the cliff to the bottom of the swing, he descends by 3.2 m. A) If the vine doesn't break, what is the maximum of the tension in the vine? B) The vine will break...

Homework Statement A ball with mass, m is released from rest at a height, h1 and is allowed to roll down a ramp. After wrapping around a loop, it rolls up an incline of angle theta to height, h2, from which it launches. We measure the horizontal distance, d, it travels. To investigate the...

Homework Statement The figure, redrawn from Gray's Anatomy, shows the tension of which a muscle from its maximum length L, so that at x=0 the muscle has length L, and at x=L the muscle would theoretically have zero length. In reality, the muscle is extended to its maximum length, at x=0, it is...