Conservation Definition and 999 Threads

Homework Statement Two pieces of clay collide and stick together. During the collision, which of these statements are true? (a) Only the momentum of the clay is conserved, (b) only the mechanical energy of the clay is conserved, (c) both the momentum and the mechanical energy of the clay are...

Homework Statement It's a simple problem, you kick a ball with an initial velocity of 5.4 m/s, the angle is 30 degrees. So the question is when does it land on the ground? So I thought that I could find final velocity so that I can use V = V(initial) + acceleration * time. My question is, can...

I've read that they must be calculated in the same frame , and so to calculate them in the easiest frame.. * So for a collision when I compute the momentum before and after I should do this in the easiest frame. Considering a specific collision where we are computing the minimum energy to...

Momentum in rigid bodies; In this problem when I draw all the forces acting on the disc A, would the reactions: Ax, Ay; W, Friction, normal force; I do not understand is how to check that Ay = W, that's what I understand from the solution. Anyone have any tips on how to treat reactions in such...

Homework Statement If you dive into water, you reach greater depths than if you do a belly flop. Explain this difference in depth using the concept of conservation of energy. Explain this difference in depth using what you have learned in this chapter**. ** It is referring to the chapter of...

Homework Statement [/B] A wheel rolls without slipping on a plane, what magnitudes are conserved? The Attempt at a Solution . [/B] I don't know if the static friction force does any work. Energy won't be conserved if it does.

Homework Statement A 900-kg car initially at rest rolls 50m down a hill inclined at an angle of 5.0^o. A 400-N effective friction force opposes its motion. (a) How fast is the car moving at the bottom? (b) What distance will it travel on a similar horizontal surface at the bottom of the hill...

Homework Statement An engineer is designing a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers...

Homework Statement Mass 2 collides with mass 1 as shown in the image, mass 1 is attached to the stick and it is initially stationary. Consider that the stick is massless and can rotate around the point O. The entire system is on a frictionless table. Which magnitudes are conserved in the system...

Homework Statement The potential energy for a mss m = 1.0 kg moving in one dimension is given by U(x) = (2.5J) sin πx. The mass starts at x = 0 with an initial velocity v = 0.71m/s. (The plus sign means the motion is in the positive x-direction.) Describe the subsequent motion of the mass...

Homework Statement A bullet has a mass of 7.5 g. It is fired into a ballistic pendulum. The pendulum's receiving block of wood is 2.5 kg. After the collision, the pendulum swings to a height of 0.1 m. What is the approximate velocity of the bullet? m_{bullet} = 7.5g = 0.0075 kg m_{wood} = 2.5...

Homework Statement Hey guys. So I gota prove that the currents given by M^{\mu;\nu\rho}=x^{\nu}T^{\mu\rho}-x^{\rho}T^{\mu\nu} is conserved. That is: \partial_{\mu}M^{\mu;\nu\rho}=0. Homework Equations Not given in the question but I'm pretty sure that T^{\mu\nu}=\frac{\partial...

So negatives always get me, no matter what and I'm having a hard time understanding the conservation of energy. Anywho, I'll continue. In a system, oh let's say a block on a rough surface with some intitial v and kinetic energy K at point A. After it gets to B, friction has done W amount of work...

Homework Statement A student holds a book at rest on the palm of her hand. She lifts the book straight up, bringing it to rest again at a higher point. 1. Is the net work done on the book positive, negative, or zero? 2. Is the change in the gravitational potential energy positive, negative...

Homework Statement With what initial speed must an object be projected vertically upward from the surface of Earshot rise to a maximum height equal to Earth's radius? (neglect air resistance.) Apply energy conservation. Homework Equations ##E_{k_1}+E_{g_1}=E_{k_2}+E_{g_2}##, however since...

Homework Statement A 710kg car drives at a constant speed of 23m/s . It is subject to a drag force of 500 N. What power is required from the car's engine to drive the car (a) on level ground? (b) up a hill with a slope of 2.0o? Express your answer to two significant figures. Homework Equations...

Is there a formula for the moment of inertia? A thin, uniform density rod is rotating about an axis that is off the end of the rod, so it looks a bit like this: ------- | (------- is the rod and | is the axis of rotation, so the rod is rotating out of the plane of your screen) I just have...

Homework Statement In classical electromagnetism, an accelerated charge emits electromagnetic radiation. In non-relativistic limit, where the velocity of the electron is smaller than c, the total power radiated is given by the Larmor formula, to wit P=2/3*e2*a2/c3, where a denotes the...

Hi, Consider a person who holds a light source of frequency f. Consider an observer who sees this light. The energy of each photon as received by the observer is E = hf. The observer is now fixed. Now suppose that the person who holds the light source starts to move towards the observer, then...

If I understand the basics correctly, the idea behind the Large Hadron Collider is to discover de Higgs boson. To do this, they accelerate protons to 99,99999% the speed of light. I think it was Einstein who said that no particle with mass can ever reach the speed of light, there is a physical...

Homework Statement A mass starts from rest and slides a distance d down a frictionless θ deg incline. While sliding, it comes into contact with an unstressed spring of negligible mass, as shown in the figure below. The mass slides an additional distance as it is brought momentarily to rest by...

Homework Statement Homework Equations Conservation of energy, F=ma The Attempt at a Solution (a) By the conservation of energy, we use points A and C as the initial and final, ## \frac{1}{2} m v^2 - \frac{1}{2} m 2.5^2= (m)(g)(9.76) \Rightarrow v = 14.1 m/s ## (b) Since ## W_{nc} = \Delta...

There are two disks of the same size and mass. A 5N force acts through the center of the first and another 5N force acts through the bottom of the other. The forces both point to the right. According to what I have learned, the linear momentum of both objects will be the same, but the second one...

Homework Statement To help keep his barn warm on cold days, a farmer stores 859 kg of solar-heated water (Lf = 3.35E+5 J/kg) in barrels. For how many hours would a 2.02 kW electric space heater have to operate to provide the same amount of heat as the water does, when it cools from 11.3 to 0 °C...

Homework Statement A 20.0 kg cannonball is fired from a cannon with a muzzle speed of 1000 m/s at an angle of 37.0° with the horizontal. A second ball is fired at an angle of 90.0°. (a) Use the isolated system model to find the maximum height reached by each ball. (b) What is the total...

Hello =) I have a question regarding the conservation of probability in quantum mechanics. We know that the probability of a measurement of a given observable, is preserved in time if the observable commutes with the Hamiltonian. But this is also true if the value of the measurement...

Homework Statement Could someone please let me know if this is correct? I'm unsure about matter always being conserved, does it change whether we're talking about Newtonian physics or special relativity? To me, matter is conserved regardless but maybe there is something I don't know...

A 0.150-kg frame, when suspended from a coil spring, stretches the spring 0.070 m . A 0.200-kg lump of putty is dropped from rest onto the frame from a height of 30.0 cm Find the maximum distance the frame moves downward from its initial position. To start off the question, I found the...

Homework Statement Practice problem for midterm. Homework Equations [/B] T_1+U_1=T_2+U_2 U_spring=1/2kx^2The Attempt at a Solution [/B] Set X-axis along the 30 degree line and the Y-axis perpendicular. I'm not sure how to consider the friction constant into the formula. Any help is very...

Hello, Could someone please provide me with a elastic collision problem where there are two objects one object with an initial velocity=0 m/s and the other object with a final velocity= 0 m/s. Thank you

Homework Statement PLEASE HELP: A bead at the end of a vertical spring moves without friction along a horizontal wire. WHen the spring is perfectly vertical , the spring is neither stretched or compressed. Show that the bead experiences a restoring force, and that if x is small, then the...

Homework Statement During a rockslide, a 710 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of kinetic friction between the rock and the hill surface is 0.23...

When do one use the principle of conservation of mechanical energy to find the velocity of a mass, and when would you use the sum of forces equals to the mass times acceleration, and there after use a ds=v dv in order to find the velocity. The specific question related to this is a spring fixed...

Homework Statement Gayle runs at a speed of 4.20m/s and dives on a sled, which is initially at rest on the top of a frictionless snow-covered hill. After she has descended a vertical distance of 4.77m, her brother, who is initially at rest, hops on her back and together they continue down the...

Hi, I have some trouble understanding if linear momentum and angular momentum (and their conservation laws) are completely independent or not. For example, one can calculate the angular momentum of a uniformly moving body with respect to a fixed point in space and show that it is indeed...

::A skier of mass 63.0kg starts from rest at the top of a ski slope of height 62.0m .A skier of mass 63.0kg starts from rest at the top of a ski slope of height 62.0m .A) If frictional forces do −1.00×104J of work on her as she descends, how fast is she going at the bottom of the slope? Take...

Energy conservation violation First of all, I would like to say that this model is NOT a perpetual motion. It will stop eventually. What I want to say here is that the output useful work seems to be greater than input energy My system consists of 2 elements. Each element is a cylinder put on...

Hello Forum, The conservation of linear momentum is applicable when the net external force is zero or negligible compared to the internal forces. This principles is applicable to perfectly elastic, partially elastic and totally inelastic collisions. But only for perfectly elastic collisions the...

Homework Statement Prove $$ j^{\mu} = j_ {EXTERIOR}^{\mu} + j_ {INTERIOR}^{\mu}$$. Writing $$j_ {EXTERIOR}^{\mu}$$ in terms of the energy-momentum tensor. Prove $$j_ {EXTERIOR}^{\mu}$$ is related to the Orbital Momentum and $$j_ {INTERIOR}^{\mu}$$ to the spin.Sorry, for the lane shifts...

Homework Statement The pendulum shown (http://puu.sh/chwMZ/90f4b96fb1.png ) swings freely, turning around at a height of 10 cm above the lowest point in its swing. It has an unknown mass, but air resistance can be ignored. a) Use energy conservation to find its speed at the lowest point of...

Homework Statement A ball of mass 1 Kg is dropped from a height of 7m and rebounds to a height of 4.5m Calculate: its kinetic energy just before impact the initial rebound velocity of the ball and kinetic energy. Account for loss of kinetic energy on impact...

Homework Statement In the Compton Effect, which of the following is conserved? Select all that apply: Total relativistic momentum. Total energy of the photon. Rest mass energy of the electron. Total relativistic energy. Relativistic kinetic energy of the electron. Net charge. Homework...

Homework Statement Two objects of equal mass traveling toward each other with equal speeds undergo a head on collision. Which one of the following statements concerning their velocities after the collision is necessarily true? (a) They will exchange velocities. (d) Their velocities will...

Homework Statement A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero Newtons. Which one of the following statements concerning this event is true? (a) Kinetic energy is conserved in this...

Hi all, I'm not 100% sure this belongs in this topic but it was a problem I was given in a quantum mechanics lecture so here goes, sorry if I am wrong.Anyway I was given a hamiltonian H= T+VWhere T is kinetic energy and av is potential, and asked to use dH/dt= 0 to find an analogy between...

Homework Statement Good morning/ afternoon I have a doubt about relativistic collisions, any help will be welcome. Consider the process of annihilation electron-positron to two photons. Calculate in the centre of mass system the wavelength of photons produced using momentum of e+e-...

Hello, Suppose that an object of rest mass m0 travels to the right with speed v1. A photon of frequency f also travels to the right and hits the object. The photon is fully absorbed by the object and then the object travels to the right with the (unknown) speed v2 after collision. Now, the...

Homework Statement A child slides without friction from a height h along a curved water slide (Fig. P5.44). She is launched from a height h/5 into the pool. Determine her maximum airborne height y in terms of h and η. (Use q for η and h as appropriate.) (Fig. P5. 44) Homework Equations I know...

Homework Statement Use energy conservation to answer the following question. A mass is attached to one end of a massless string, the other end of which is attached to a fixed support. The mass swings around in a vertical circle as shown. Assuming that the mass has the minimum speed necessary at...