Conservation of energy Definition and 1000 Threads

Homework Statement An outfielder throws a baseball with an initial speed of 79.0 mi/h. Just before an infielder catches the ball at the same level, its speed is 65 ft/s. How much of the ball's mechanical energy is dissipated by air drag? (The weight of a baseball is 9 oz.) Homework Equations...

Homework Statement A .500 kg block rests on a horizontal, frictionless surface as in the figure below. The block is pressed back against a spring having a constant of k=625 N/m, compressing the spring by 10cm to point A. Then the block is released. a) Find the maximum distance d the block...

Hi, With permanent magnets I have been puzzling over how they can obey the conservation of energy. If I make a permanent magnet then I can use it, expending negligible energy myself, to attract, and thus give kinetic energy to, many other metallic objects. So, when I create my magnet...

In an AP Physics C course for mechanics, what other variables are usually added to this equation? : U_g+U_{sp}+K+W_{nc} = U_g+K Also, why is a spring's potential energy only on the left hand side? Would it ever go on the right hand side? (final).

The coefficient of friction between a 3 kg block resting on a flat table, is 0.400. A 5 kg mass is hanging off the table attached to the first mass by a lightweight rope on a frictionless pulley. The system starts at rest. What is the speed of the 5 kg ball when it has fallen 1.5 m...

Homework Statement A 2 kg ball is attached to the bottom end of a length of fishline with a breaking strength of 44.5 N. The top end of the fishline is held stationary. The ball is released from rest with the line taut and horizontal (theta = 90 degrees). At what angle theta (measured...

Homework Statement Homework Equations ΔK1+ΔK2+ΔU1+ΔU2 = 0 The Attempt at a Solution The biggest stumbling block I have is setting up the initial and final conditions. First the initial: 1)Does m1 have potential energy in this setup? Part of me thinks it would have m1gh but I...

Homework Statement A mass m = 2 is in free fall. The acceleration of gravity is g = 10. All numbers are in mks units. The position y(t) and velocity v(t) of the mass as a function of time t are y(t)=9−5t2 and v(t)=−10t. Find each of the energies (K,U,E) as a function of time t. Hint...

Homework Statement A 60.0 kg skier starts from rest at the top of a ski slope 60.0 m high. Homework Equations The Attempt at a Solution (a) If frictional forces do -10.5 kJ of work on her as she descends, how fast is she going at the bottom of the slope? This one I got correct...

Homework Statement Given: \frac{1}{2}m (\dot x)^2 + mg x = E Gravitational force is mg. We need to show that by solving this DE that we can confirm that the conservation of energy correctly describes one-dimensional motion (the motion in a uniform field). That is, that the same motion...

Homework Statement Given: \frac{1}{2}m (\dot x)^2 + mg x = E Gravitational force is mg. We need to show that by solving this DE that we can confirm that the conservation of energy correctly describes one-dimensional motion (the motion in a uniform field). That is, that the same motion is...

After looking at Umklapp scattering, I believe I have finally gotten most of it down, but a few things are still not clear. 1) Momentum is not conserved for certain phonon collisions, and a certain number of reciprocal lattice vectors are transferred to the crystal lattice...

Hi all, I was talking to my professor about the black hole information paradox, and all of this got me to thinking about something: Why do you think the conservation of energy is so vital to the existence of the universe? Suppose we didn't conserve energy, but actually lost it in very...

Homework Statement A block of mass m starts from rest at a height h and slides down a frictionless plane inclined at angle θ with the horizontal, as shown below. The block strikes a spring of force constant k. Find the distance the spring is compressed when the block momentarily stops...

Homework Statement A 2-kg block is attached to a horizonal ideal spring with a spring constant of 200N/m. When the spring has its equilibrium length the block is given a speed of 5m/s. What is the maximum elongation of the spring. Homework Equations Conservation of mechanical energy...

http://www.natuurkunde.nl/servlet/supportBinaryFiles?referenceId=1&supportId=606217 Hello everyone, I was wondering if anyone could shed some light on the following problem: While composing a practise test for a chapter about conservation of energy, I made a problem like the one in the...

Homework Statement Consider an elastic collision between two bodies of equal mass, one of which is initially at rest. Let their velocities be \vec{v_1} and \vec{v_2} = \vec{0} before the collision, and \vec{v_1 '} and \vec{v_2 '} after the collision. Write down the vector equation representing...

The studio explores the conservation of energy using the Interrupted Pendulum apparatus shown in (Figure 1). A ball is attached to a horizontal cord of length L whose other end is fixed. A peg is located at a distance d directly below the fixed end of the cord. The ball is released from rest...

Thermodynamics is clearly based on the assumption that energy is conserved. I ended up discussing this assumption with a fellow student, who states that this assumption can be rigidly justified and means that Noether's theorem proves this. Everywhere I have read about it, the conservation of...

The CMB used to be gamma rays, right? And now it's microwaves - more redder energy: so where did the rest of the energy go?

Hi, I have a somewhat silly question about something I cannot figure out properly. I have a cylinder with a piston inside. The cylinder is sealed and filled with air. The piston is free to move back and forth inside the cylinder, but are also sealed so no air can escape no matter how much...

Homework Statement http://grephysics.net/ans/9277/87 Can somebody explain to me why the electric potential = -K/2r^2? If you integrate Fdr and F = K/r^3, where does the 2 in the denominator come from?

Hi, Is the fact that the expansion of the universe accelerates consistent with the conservation of energy? If so, how? Grateful for response!

I know that the Law of Conservation of Mechanical Energy can be derived using Newton's Laws and Kinematics. I believe that at very small scales, where Newton's Laws no longer apply, that Conservation of Mechanical Energy is still true (or is it Conservation of Energy in general, not sure). 1)...

Homework Statement A yo-yo has mass 0.8 kg and rotational inertia 0.12 kg m2 measured about an axis perpendicular to the screen and passing through its center of mass. A light thin string is wrapped around the central part of the yo-yo that has radius 0.03 m. The string is attached to the...

Hi guys, let's say we have a wave where the power P is proportionate to the square of its amplitude, which is A^2. If now we have 2 identical waves in superposition in phase, then we have an amplitude of 2A am i right? Next, we realize that because of the amplitude of the superposed waves is...

This is an attempt by a novice to do something neat. Please feel free to correct me. I am trying to see if one can derive the Hamiltonian equations of motion from a simple statement of the conservation of energy for mechanical systems. My attempt: 1. For a system S with position q and a...

Two blocks with different mass are attached to either end of a light rope that passes over a light, frictionless pulley that is suspended from the ceiling. The masses are released from rest, and the more massive one starts to descend. After this block has descended 1.24 m, its speed is 3.27 m/s...

When the water receives energy from the sun, the water on the surface will have an increased temperature and may evaporate and float up to form clouds. This seems like common sense but where did the water gained the gravitational potential energy? The increased temperature the water has must...

Q:A 46 g steel marble collides obliquely with an identical stationary marble, and continues at 55 to its original direction. The collision is perfectly elastic. What is the angle between the direction taken by the target ball and the original direction of the incident ball? I know the...

Homework Statement Two charged particles connected by a string exert electric forces on one another. One has a mass of 3 grams and the other 6 grams. The string is .04m. The force is calculated to be 50.56N. What is the tension in the string? What is the total energy of the system...

Homework Statement Use energy to show whether or not the data agrees with the law of conservation and explain. Mass-.3105kg spring constant-6.412 Equailibrium position-1.082 Max positive postion (1) farthest distance to the right of the equlibrium position time-3.70s...

Homework Statement The 100kg crate shown in Fig. 1 is acted upon by a force having a variable magnitude P = 20t N, where t is in seconds. Determine the crates’ velocity 2 seconds after P has been applied. The initial velocity is v1=3m/s down the plane, and the coefficient of kinetic...

From the wiki page on Hermann von Helmholtz: "an 1847 physics treatise on the conservation of energy was written in the context of his medical studies and philosophical background. He discovered the principle of conservation of energy while studying muscle metabolism. He tried to demonstrate...

I don't understand how lenz's law is a form of energy. An explanation said if the induced current did not oppose change, we would be obtaining energy without doing any work. I think my problem here is that I can't follow the no change -> get free energy logic.

I am a bit confuse about gravity and work Suppose a ball falls from one height to another, hi to hf When talking about the system BE the ball AND the earth, all the work done is internal, and no external work, change in KE = change in PE, right? But when talking about the system B of just...

Homework Statement A block slides from rest down a frictionless ramp which is 4 m long and has a 30 degree angle with respect to the ground. After reaching the bottom of the ramp it slides on a frictionless surface and compresses a spring a distance of 12cm (.12m) before coming to rest...

As the expansion of space accelerates, space is created and this seems to break the conservation of energy law. I've googled this but have not found a really good explanation of this. Imagine for a moment we're so far into the future that there are vast vast voids between what remains of...

Homework Statement Hi, I am having trouble with this problem. I'ld be very grateful if anyone could help me :) I've only done it with the conservation of energy way because I am not too sure how to go about it with the D'alembert principle. A Car with a mass of 100kg is pulled along a...

Homework Statement A particle with rest mass m_{0} and kinetic energy 3m_{0}c^{2} makes a completely inelastic collision with a stationary particle of rest mass 2m_{0}. What are the velocity and rest mass of the composite particle? Homework Equations T = (\gamma - 1)m_{0}c^{2} = E -...

Hi guys, I've realized that to truly, deeply, and fully understand something it often helps if you think about the conservation of energy, and then just build up from that. So here I have tried to explain why a battery has a voltage, and why there are voltage drops across resistances...

Here is the question: Here is a link to the question: I need help in physics!? - Yahoo! Answers I have posted a link there to this topic so the OP can find my response.

Hello! When studying the law I noticed that the change in magnetic field (i.e the magnet's motion) is = to the EMF induced. That proofs to me how the principle of the conservation of energy is applied to the world of electromagnetism as well! The energy applied to move the magnet is...

1. a student throws a ball down with an initial velocity of 5.0 m/s from a point 8.0 m above the base of a track. Find the speed of the ball as it hits the base of the track. The track is designed to losslessly change the direction of the ball up a frictionless ramp. What is the height above...

Energy -- Cannon Ball and Conservation of Energy Homework Statement A cannon tilted up at a 30.0 angle fires a cannon ball at 80m/s from atop a 10m -high fortress wall. What is the ball's impact speed on the ground below?Homework Equations Conservation of Energy Ugi+KEi= KEf *please note...

This is not a homework question. An adult exerts a horizontal force on a swing that is suspended by a rope of length L, holding it at an angle θ with the vertical. The child in the swing has a weight W and dimensions that are negligible compared to L. The weights of the rope and of the seat...

Hi. I saw this: http://physics.stackexchange.com/questions/35431/is-the-law-of-conservation-of-energy-still-valid Now, if that's the case, then I wonder about a related question: can general relativity be used to create perpetual motion machines? If not, then why not (i.e. how does energy...

Homework Statement A satellite is in an elliptic orbit around the Earth. Its speed at pedigree A is 8650 m/s. (a) Use conservation of energy to determine its speed at B. The radius of the Earth is 6380 km. Use conservation of energy to determine the speed at the apogee C. Homework...

This is from an old course I took. I'm not sure what I'm doing incorrectly. Homework Statement Two identical bowling balls are rolling on a horizontal floor without slipping. The initial speed of both balls is V = 9.9 m/s. Ball a encounters a frictionless ramp, reaching a maximum height...

Momentum and magnetic fields are both vector quantities. If two bodies with the precise mass and speed collide head on (θ = 0), then momentum is conserved (they come to a complete stop) and energy is conserved (the kinetic energy is changed to other forms). What then happens in the case of...