Conservation of energy Definition and 1000 Threads

Homework Statement A light rod ##AB## of length ##2a## has a particle ##P## of mass ##m## attached to ##B##. The rod is rotating in a vertical plane about a fixed smooth horizontal axis through ##A##. Given that the greatest tension in the rod is ##\frac {9mg}{8}##, find, to the nearest degree...

Homework Statement Homework Equations ΔEsystem + ΔEsurroundings =0 The Attempt at a Solution I have solved 11a and got 5m/s. I can do 11b just by just jumping to Ek = Fs (from the work kinetic energy theorem), but I would like to do it formally from first principles using the Law of...

Anyone know if the following statement is true (and why)? "Getting to higher ground would increase his gravitational potential energy, decreasing the effects of non-conservative forces, which would allow him to move easier." CLARIFICATION: "move easier" refers to a lack of friction and not the...

Homework Statement I have a question asking me to find the launch speed of a ball (mass 0.39kg) when released by a spring mechanism made of 2 springs each with force constant 25Nm^-2. they are pulled back 12 cm. the ball is initially at rest.Homework Equations [/B] v^2=u^2+2as f=ma f=kx...

Homework Statement There is a 4 kg mass that has a speed of 6 m/sec on a horizontal frictionless surface. The mass collides head-on and elastically with an identical 4 kg mass initially at rest. The final speed of the first 4 kg mass is: (a) 0 m/s (b) 2 m/s (c) 3 m/s (d) 6 m/s Homework...

If velocity is reference frame dependent then kinetic energy should also be. Considering this we will have different energies in different frames. Doesn't it violate conservation of energy?

Am I correct in understanding that locally, ie, with respect to circumscribable phenomena, conservation of energy is valid in the cosmos but that otherwise it is/may not be? Otherwise said, the source of dark energy does/may not obey this principle? Or is this a question that does not fall...

Homework Statement In the document below I need to try and find the angular velocity I need help on part b Homework Equations F=ma KE_Translational= 0.5mv^2 KE-Rotational= 0.5Iw^2 Assuming g=10m/s^2 The Attempt at a Solution I have the answer key attached with the question but I am not sure...

Homework Statement A block with a mass of 5kg is pulled up an incline with a 20 degree incline, the coefficient of friction is 0.2 and the distance 10 metres. The block accelerates from 1m/s at point A to 5m/s at point B. I have to use both D’Alembert’s and Conservation of energy principles...

Alright, so this has been bothering me for awhile, and the more I think about it, the more it bugs me. I'm almost guaranteed wrong about what I'm going to say here, but I'm not sure why I'm wrong, so hopefully someone here can explain my wrongness to me. Unfortunately, this is going to take...

Homework Statement Homework EquationsThe Attempt at a Solution I understand how they got Q1 and Q2 for the first two columns, but how am i suppose to find Q1 and Q1 for the 3rd and 4th event? Isn't it just 0? Cause it seems like the temperatures just stayed constant. I'm not entirely sure...

Homework Statement In a waterfall about 20 billion liters of water per hour drop about 110 m. What is the increase of the water temperature, assuming that the entire gain of heat is transferred to the water? Homework Equations I'm more curious about the question in itself. Perhaps I'm missing...

Homework Statement This problem comes from the Feynman Lectures. However, the author doesn't explain in detail the procedure to solve the problem. I have to calculate the weight W using only the law of energy conservation. Homework Equations In the second picture W it is lowered of 5...

Homework Statement Mass 1(75kg) glides on ice at 1.8 m/s to a second stationary mass, (52 kg) How far will the pair slide after the collision if the coefficient of kinetic friction between the ice and their skates is .042? Homework Equations Conservation of energy, Kinetic Energy, Work...

<Moderator's note: Moved from a technical forum and thus no template.> I'm not sure how they got the extra (1/2)mv^2? My question is shown using pink font in the image below as well as my attempt.

The energy and momentum of a closed system is always conserved. If a laser can emit perfectly parallel and perfectly superimposed light waves (occupy the exact same space) that are perfectly 180° out of phase and of the same frequency, what can be said about the energy and momentum of the...

I’m a bit stuck with differentiating between the conservation of energy and D’Alambert. For a question I need to find the average resistance of the ground after it has been struck by an object. I chose to look at the equation as Ma + Mgh - Fr = 0. Can you advise if this is correct?

Hi everyone! I'm here for a little conveyance towards a question that is disturbing me for days. Just suppose, you and I design a hydroelectric generator that provokes energy from the downflow of precipitating rain. These falling drops of rain surely have originated from the vapours of the...

A cylindrical container of water has a diameter of 7.98 m and a perpendicular height of 2 m. It is filled with water (1000 kg = 1000 l) and placed on top of a 4 m stand. Calculate the: A) potential energy of the water B) kinetic energy of 20 kg of water just before it reaches the ground, if the...

Where does the Coefficient of Restitution equation come from, in terms of the Conservation of Energy? The measure of efficiency is the velocity after the collision divided by the velocity before the collision, but how does it get to that point? I'm trying to view this focused on an object that...

Homework Statement A child goes down a water slide. The slide is 9.0 m tall. She pushes off with an initial speed of 2.0 m/s (in the horizontal direction). If the slide is frictionless, how fast will she be going at the bottom of the slide? Homework Equations In the book, they use a...

Homework Statement 14.37 A 75-kg ski jumper starts his run in the position shown on the parabolic track. The equation of the parabola is ##y = (12/225)x^2##, where x and y are in meters. Neglecting friction, calculate the contact force between the skis and the track at O. Homework...

Homework Statement 14.34 The 0.5-kg bob of the pendulum travels a complete circle about the pivot point O. Determine the smallest possible speed of the bob in position A if it is suspended from (a) a rigid rod of negligible mass; and (b) a string Homework EquationsThe Attempt at a Solution...

Homework Statement 14.27 The 2.5-kg weight is released from rest in position A, where the two springs of stiffness k each are undeformed. Determine the largest k for which the weight would reach position B Homework EquationsThe Attempt at a Solution Hi. Can you check if I am going at...

I'm having trouble seeing how electric potential energy production on a conductor follows conservation of energy. Let's use the photoelectric effect as an example. A photon with energy E = hν strikes a conductor, ejecting a photoelectron with a maximum kinetic energy of hν - φ. Assuming the...

Homework Statement 14.28 The spring of stiffness k is undeformed in the position shown. The 30-g ball is placed on the spring and launched vertically by compressing the spring 150mm and releasing it. If the ball reaches an elevation of 14.25m above A, determine the value of k. Homework...

Homework Statement Homework Equations ∑F=ma W = - ΔUs ΔUs = 0.5 k (xƒ)^2 - 0.5 k (xi)^2 W = ΔUs + ΔKE d = viy t + 0.5 * t^2 * a The Attempt at a Solution A) [/B]W = - (0.5 k xƒ^2 - 0.5 k xi^2) = - (0-100) W = 100 J B) W = ΔUs + ΔKE 100 = 0.5 m vf^2 -0 + 0 - 0.5 k xi ^2 100 = 0.5 * 2 * vf^2...

Homework Statement A toy car has a mass of 2 kg moves with initial speed of 2 m/s on a rough horizontal plane of μκ=0.14.A spring with constant of 250 N/m is fixed. Which of the following statements is true ? A) The toy does not approach the spring B) The toy just touch the spring[/url][/IMG]...

I don't know much about classical physics(such as lagrangian function), but as i was reading conservation of energy, i came to this theorem and it tells that if a system is symmetrical in certain transformations(such as translation, rotation etc) then it will have a corresponding law of...

Homework Statement 14.10 Solve Prob. 12.47 by the work-energy method 12.47 When the 1.8-kg block is in the position shown, the attached spring is undeformed. If the block is released from rest in this position, determine its velocity when it hits the floor Homework EquationsThe Attempt...

[Moderator's Note: Thread title changed to better reflect the problem statement] Homework Statement A body of mass m is on a disk of mass M=2m and radius R, initially static and free to spin around its center. The mass mm goes around a trajectory described in the image below with constant...

Homework Statement Homework Equations W spring = 1/2kx^2 Ug = mgh The Attempt at a Solution I have the work in the above problem, but I'm kinda confused how there is any potential energy here besides the spring potential energy that we get in the final state. Why is mgh here mgx? why can h...

What is ΔEp = ΔEk + W I have come across this formula, but i haven't seen it before. What is it used for?

Homework Statement I'm sorry but I don't have the exactly problem written down but I know the givens. So the question involves finding work done on a pendulum hanging from the ceiling. Homework Equations I was given the the length of the string is 1m. That a mass hangs at the bottom of...

Homework Statement [/B] I have created a very simple Rube Goldberg device in Algodoo, and I need to analyze 3 correlating steps within it, using physics descriptives and equations. My primary focus is the ball as it hits the windmill, which I need to describe and calculate its velocity at that...

Homework Statement A particle of mass m is dropped from a height h, which is not necessarily small compared with the radius of the earth. Show that if air resistance is neglected, the speed of the particle when it reaches the surface of the Earth is given by ##\sqrt {2gh}## ##\sqrt {\frac {R_E}...

I am finishing up a lab write up for conservation of energy, where we launched a projectile into the air and measured the initial velocity and height of the projectile. ( 10 trials) One of my questions asks if I wanted the ball (projectile) to travel twice as high, how much faster would it have...

Homework Statement "Consider a 250 gram block on a 10 degree frictionless incline and in contact with a spring of constant 1.2 N/cm. If the block is launched from rest by the spring with an initial compression of 6cm, how fast is the block moving at the point of release from the spring? How...

Is it accepted that the law of conservation of energy can be considered in a non-local context? If this is not accepted, then why not?

Dear Everybody There is a ball which has mass of 11 grams is thrown straight up with an initial speed of 4 m/s. Assume the air drag is negligible. a. What is the kinetic energy of the ball (in J) as it leaves the hand? b. How much work is done by the gravitational force during the ball's rise...

1. Two identical charged particles which are point masses are fastened to the two ends of a spring of spring constant 100 N/m and the natural length 10cm.The system rests on a smooth horizontal table.The charge of each particle is 2*10^(-8)C.the extension of spring if the extension is small as...

I go to work on the train and I get on at the back and get off at the front. I can choose when to walk through the train. If I walk when the train is accelerating forwards it is harder for me to get to the front and I do more work. If I make the trip when the train is stopped or at a constant...

Homework Statement Two springs which have spring constant of k1 and k2 respectively are vertically hung in a series. Then, a mass m is attached to the end. Find the displacement and the spring constant of this series. Homework EquationsThe Attempt at a Solution I got the displacement x1+x2...

I am no able to understand the reasoning of Feynman in deducing that it is impossible to build a machine that will lift a weight higher than it will be lifted by a reversible machine. I am also not able to understand what reversible machine is. So, please help me.

Let's consider a setup consisting of a table with friction, and a block on top of it. Suppose we drag the block across the table with a constant speed. The applied force ##f_{app}## acting through a distance ##d## does a work ##f_{app}d##. The frictional force ##\mu N## is equal to ##f_{app}##...

In free space there are two masses: - Metallic sphere of mass M, radius R and total charge equal to 0. It has also a resistivityρ. - Metallic sphere of mass m, radius r and charge q. The distance between the masses is D. We can assume r <<R<<D and m<<M. The masses start accelerating until they...

Homework Statement [/B] A block of mass, m, is dropped from height, h (above the plate), onto a plate of mass, M, which is attached to a spring with spring constant, k. The block sticks to the plate and the system starts to oscillate. What is the amplitude of the oscillations. Homework...

Homework Statement A satellite is orbiting the Earth around an orbit of radius R=2.5R0, where R0 is Earth's radius. What additional velocity is needs to be directed along the radius of the orbit so that satellite escapes Earth's gravity? Homework Equations Total Energy= K + U Conservation of...

As a spinning mass is unwound, angular momentum is conserved, meaning ##Iω## remains constant. However, since rotational energy is proportional to the square of the angular velocity, how is it possible for energy to be conserved as well?

Homework Statement A billiard ball moves at a speed of 4.00 m/s and collides ELASTICALLY with an identical stationary ball. As a result, the stationary ball flies away at a speed of 1.69 m/s. Determine a. the final speed and direction of the incoming ball after the collision b. the direction...