Energy conservation Definition and 434 Threads

Homework Statement If the car is given an initial speed of 4.0 m/s, what is the largest value that the radius R can have if the car is to remain in contact with the circular tract at all times? See the attached file (named: car.pdf) for the drawing. Homework Equations PE=mgh ----> Formula for...

Why am I getting a negative!? (Energy conservation) Homework Statement 2kg block slides on a rough table with uk = 0.3, just before the block hits the spring V0 = 1.3 m/s. k = 120N/m. How far is the spring compressed? Homework Equations Ki + Us = Kf + Us - Eth The Attempt at a...

Hello again, The question and free body diagram as well as my attempt at the solution are all in the attached photo. Thanks in advance!

Homework Statement It's been a great day of new, frictionless snow. Julie starts at the top of the 60 degree slope shown in the figure . At the bottom, a circular arc carries her through a 90 turn, and she then launches off a 3.0--high ramp. How far horizontally is her touchdown point from...

I need help! Homework Statement A 44.0 g ball is fired horizontally with initial speed vi toward a 110 g ball that is hanging motionless from a 1.10 m-long string. The balls undergo a head-on, perfectly elastic collision, after which the 110 ball swings out to a maximum angle = 52.0...

I did a thought experiment for myself today to test whether energy is conserved in Lorentz transformations. I chose to consider three objects lying on a horizontal line. In object 2's rest frame, object 1 has a velocity of 0.600c to the left, and object 3 has a velocity of 0.600c to the...

A 1kg block is at rest on a horizontal frictionless surface touching the end of an unstretched spring of spring constant 200N/m. Tjhe other end of the spring is fixed to a wall. A 2kg block traveling at a speed v(initial)=4m/s collides with the 1kg block, and the two blocks stick together. I...

Homework Statement A 2.30 g bullet embeds itself in a 1.6 kg block, which is attached to a spring of force constant 770 N/m. A) If the maximum compression of the spring is 5.40 cm, find the initial speed of the bullet. Homework Equations Step one: convert everything to kg and m Step two: 1/2...

Homework Statement a toy race car of mass m is released from rest on the loop-the-loop track. if it is released at a height 2R above the floor, how high is it above the floor when it leaves the track, neglecting friction? (the radius of the loop is R) Homework Equations E=K+U The...

Homework Statement An object of mass 0.2 kg with initial velocity 4.8 m/s slides a horizontal distance of 3.0 m before coming to rest (final velocity is 0 m/s). What is the coefficient of kinetic friction on the surface? Homework Equations K + U - W(other) = 0 ...conservation of energy...

This isn't really a homework question, so I'm hoping I can just get a straight answer from someone (although it is related to questions). I realize that you can choose U = 0 anywhere you want in a gravity-related problem, ideally choosing a place where it is easiest to manipulate mgy values...

Homework Statement Using conservation of relativistic energy and momentum, show that for Compton scattering from a free electron, the energy-angle formula for the electron is T=m_0c^2\frac{2\alpha^2cos^2\phi}{1+2\alpha+\alpha^2sin^2\phi} where T = kinetic energy given to electon...

Hi, I've managed to get extremely confused; I feel like I'm getting told different things! I hope someone can just clarify this for me. If you have a reaction, say for example: p pion+ --> p p (where p is a proton) is it true that the rest mass afterwards must be less than the rest mass...

A .145kg drop from sixth story building window. If each story is 2.5m tall, use energy conservation to find the rock velocity when it strikes the ground. (ignore air resistance) I have: mass .145kg h 2.5m each story 2.5m * 6 = 15m (total height) gravity 9.8ms^2 V=? I am confuse, what...

Hello everyonea. I was studying special relativity and i got stuck on an example. Here it is:'to an observer,two bodies of equal rest mass collide head on with equal but opposite velocities 0.8c and cohere. To a second observer,one body is initially at rest. Find the apparent velocity of the...

A classic problem in freshman electrodynamics is as follows: We have a capacitor (capacitance C1) charged up w/ charge Q, which means the energy in the system is: U_1 = \frac{Q^2}{2C_1}. We then disconnect the battery, and connect a second capacitor (capacitance C2) in parallel w/ the...

In introducing the concept of 'virtual photon',Halzen Martin writes (ch#1,P#7) "An ekectron emits a photon (the quantum of electromagnetic field) and as a result,recoils in order to conserve momentum.it is clearly impossible to conserve energy as well,so the emitted photon is definitely not a...

While just standing on creaking floorboard, i was thinking about where the energy came from to create the noise. I assume it came from me moving my mass over the creaky point, therefore do i lose more energy walking on creaky floorboards than just normal floorboards?

Suppose we have two pendulums of equal natural frequency set up like a Barton's pendulums system (hung on a common string). If we oscillate one of the pendulums, the other will also oscillate due to resonance. Supposing it's an ideal system where there is no friction. If we release the...

The probability of finding the particle inside the wall is non-zero, What happen if we do find the particle is inside the wall, would that violate energy conservation? since total energy is smaller than the potential energy of the wall

Homework Statement A spring is pulled back and launches a ball. The ball flies into the air at a perfectly horizontal angle. How far will the ball go before it hits the ground? Variables for the FINAL equation are: ∆x - distance the spring is pulled back g - acceleration of gravity m - mass of...

I've been fooling with this problem for quite some time now and I'm not sure where I'm going wrong. Any help would be appreciated. Homework Statement The two problems below are related to a cart of mass M = 500 kg going around a circular loop-the-loop of radius R = 12 m, as shown in the...

Hi, I've read that Kirchhoff's first rule is a statement of electrical charge conservation. However, currents are electrical charge in movement, so isn't it possible to say that it also follows the law of conservation of energy? Thanks.

This is a spin off from another thread ( https://www.physicsforums.com/showthread.php?t=310455&page=2 ) to avoid hijacking the original thread. DrGreg offered this expression for Potential Energy from the textbook "General Relativity" by Woodhouse: PE = m_o c^2*\sqrt{1 - 2GM/(rc^2)}...

1. I have to use energy conservation to determine the forces acting on the particles. 2. An isolated system consists of two particles of masses m1 and m2, whose position vectors in an inertial frame are x1 and x2 and velocity vectors are v1 and v2. The interaction of the particles can be...

I am fairly new to QM and am learning many of the basics right now. We were just discussing conservation of operators (energy, momentum, etc) and I recalled a problem proposed in my textbook about a 1D particle in a box of length L. at a time t, the box suddenly expands to t=2L, in which time...

Homework Statement Determine the total energy of an electron traveling at 0.98 c A) 0.25 MeV B) 0.51 MeV C) 0.76 MeV D) 1.8 MeV E) 2.6 MeV Homework Equations KE = 1/2 mv^2 E=mc^2 (rest energy) The Attempt at a Solution I had found the velocity for an electron by 0.98 * 3.0...

Hey all! Now I'm working on wireless communication, not a physician. In many courses in ECE, we learn about principle of superposition of radio waves. But I have a stupid question which has been considered no wonder so far. There are two radio senders(S1,S2) and one receiver(R). Let's...

Homework Statement A 1500kg rocket is to be launched with an initial upward velocity of 50m/s. In order to assist its engines, engineers will start it from rest on a ramp that rises 53 degrees from the horizontal. At the bottom, the ramp turns upward and launches the rocket vertically. The...

5) If there are no external forces acting on a system in the x direction, but there is an external force acting on the system in the y direction, then the y component of momentum of the system is constant. True False 6) If work is done on an object by only conservative forces...

Homework Statement A package of mass m is released from rest at a warehouse loading dock and slides down a 3.0-h frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass 2m, from the bottom of the chute. a)...

Homework Statement The problem A basketball player 2.00m in height throws the ball at a 40degree angle 10.0m from the basketball post and manages to get the ball through the net without it touching the backboard. If the height of the net is 3.05m from the ground, what is the initial speed...

Homework Statement An object of mass M = 4 kg slides from rest a distance d = 4 m down a frictionless inclined plane where it encounters a spring. It compresses the spring a distance D = 1 m before stopping. The inclined plane makes an angle q = 20° with the horizontal. Homework Equations...

This is my first time on physics forums, and I am glad to have the chance to participate. My questions have been asked many times by others, but after lots of research, including among these threads on physics forums, especially “hurk4” on Feb 14-07 and Will Kastens, I can find no definitive...

Homework Statement I don't know if anyone can help me with this without having done the lab, but I thought I'd give it a shot. Ok, so I did a lab in my physics class where we used little rollercoasters to find the PE and KE of a marble at various heights and speeds. Here is the question in my...

I am new to the field of relativity. I read the Lorentz transformation between different system of coordinates. I have a question. Let's suppose that we have a Doppler shifted pulse in frequency (time dilation). This pulse has the same amplitude as the pulse seen by a moving observer. That is...

Im confused with mass energy conservation. i get that mass and energy are conserved but i don't understand how mass can become energy and visa versa.. can anyone help explain it to me in another way?

I have a question with regards to the increase in mass of an an accelerated object. I actually posted this question yesterday but couldn't find it, so maybe it didn't get through... Anyway, consider 2 large masses very far away from each other. This system has a certain gravitational...

Homework Statement Hey guys. So I got this disk connected to a spring which is connected to a wall. A mass m hits the disk with a velocity v and sticks to it. The question is to find the velocity of m at point A. As you can see I used the conservation of the angular momentum to find...

1) A 900-kg car traveling east at 15.0 m/s collides with a 750-kg car traveling north at 20.0 m/s. The cars stick together. What is the speed of the wreckage just after the collision? Relevant equations: m1v1 - m2v2 = (m1+ m2) vfinal My attempt: This is an inelastic collision because the...

Homework Statement A particle P of mass m , which is on the negative x-axis. is moving towards the origin with a constant speed u. When P reaches the origin , it experiences the force F=-Kx^2, where K is a positive constant. How far does P get along the positive x-axis? Homework...

Super quick question on spring and energy conservation! Homework Statement What does conservation of energy in equation form look like for spring? Homework Equations i know that [delta]K= k-k0 i know that [delta]Ug=mgh-mgh0 idk on [delta]Us= ... The s,g stand for subscripts...

Energy conservation with a projectile -- please help! Homework Statement A 2.0 kg projectile is fired with initial velocity components Vox= 30 m/n and Voy = 40 m/s from a point on the Earth's surface. Neglect all effects due to air resistance. A) What is the kinetic energy of the projectile...

Hi all! I've been thinking of something lately. When an atom absorbs an incoming photon, the atom must gain some momentum in order to conserve linear momentum, right? Sort of like a totally inelastic collision? This momentum corresponds to some amount of kinetic energy and thus a raise in...

A 2.25-g bullet embeds itself in a 1.50-kg block, which is attached to a spring of force constant 785 N/m. If the maximum compression of the spring is 5.88cm find (a) the initial speed of the bullet and (b) the tie for the bullet-block system to come to rest I used: E = K + U =...

Let's say we have a helium balloon carrying total weight of 1 kg. We set up 2 stations. Pumping station on the ground and deflating station at certain height. We pump the balloon until it start to float up. We catch it at deflating station at height H. Now the energy we gain is potential...

Homework Statement A 10 kg vox slides 4.0 m down the frictionless ramp shown in the following link. It then collides with the spring whose spring constant is 250 N/m. a. What is the maximum compression of the spring? b. At what compression of the spring does the box have its maximum...

Considering UNIVERSE as a system , then are the black holes the elements that are present in the system so that the energy of the system remains conserved ? Is there any information on how black holes came into existence ( is it a balancing act of nature ) ? Can (energy conservation)...

Homework Statement A 2.00 kg is released on a 53.1degree incline, 4.0 m from a long spring with force constant 120 N/m that is attached at the bottom of the incline. The coefficients of friction between the package and the incline are static friction constant = 0.40, and kinetic friction...

How much does the American public know about or enable energy conservation? It seems to me that by far most effort of this kind is by industry and government. Has the informational drive to change public consumption through behavior been successful, or is the primary means the pocketbook...