Conservation of momentum Definition and 757 Threads

I know that momentum is conserved if there are no external forces. But, can you tell me what external forces are ? The site http://www.physicsclassroom.com/class/energy/Lesson-2/Internal-vs-External-Forces says that internal forces are force of gravity and force of spring. But, I think that...

I always see that a ball moving in a constant speed collide with another ball is common conservation of momentum problems. Obviously, I know that the momentum is mass*velocity But, what if the ball accelerates and collides with another ball ? I think I can't use mass*velocity for the momentum...

Hello, I recently posted a few conceptual questions regarding conservation of momentum. I'm processing the information more easily now, but I've hit yet another bump in the road. I've learned that in an inelastic collision in which "velocity is the same before and after the collision" the...

Ok, so for the derivation of the Navier Stokes, the conservation of momentum through a control volume (CV) is Time rate of Momentum Change in CV = Time rate of Momentum Change into CV - Time rate of Momentum Change Out of CV + Sum of External Forces Why is Sum of External forces in there? I...

Q. A LASER is operating at a frequency f = 6.1*10^14 Hz. A)Calculate the momentum of the photon emitted by the laser. B)A helium atom flies towards the laser at a speed of v = 3.5 m/s.During one laser pulse the gold atom absorbs on average 5 photons.Find the speed the helium atom after one laser...

Suppose you have a source of electron antineutrinos, and you arrange your apparatus so that a billion billion billion of them collide directly with a black hole. In principle, you could measure the change in momentum and energy from that occurrence. Suppose you did that the next day. According...

when two objects collide some kinetic energy can be lost to heat, so some of the kinetic energy of the two colliding objects transfers to the individual particles of these objects. Does the same thing happen for momentum?

While reading the derivation of the formula \lambda' - \lambda = \frac{h}{ m_ec}(1-cos(\theta)) on Wikipedia, they point out that the momentum gained by the electron is larger than the momentum lost by the photon: $$ p_e=\frac{\sqrt{h^2(\nu-\nu')^2 +2h(\nu-\nu')m_ec^2}}{c} >...

Say you had two boats (a and b) moving past each other without colliding and a man moved from boat a to boat b. Is it correct that boat b would decelerate and boat a would accelerate due to the conservation of momentum

What are the conditions necessary for applying the conservation of mechanical energy or the conservation of momentum? Can we apply these anywhere or do we require specific conditions which have to be fulfilled for applying them?

Homework Statement QUESTION 1 :A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force do to gravity is 0 Newtons. Which one of the following statements concerning the event is true? a) Kinetic energy is conserved in the...

Homework Statement A ball is thrown against a fixed wall where it bounces elastically. The mass of the ball is M and the velocity just before it hits the wall is U. Ignore the force of gravity in this question. a) Does the Principle of Conservation of Momentum apply to this situation? b) Obtain...

This is a modified problem from the one posted a few days ago. I’ve been unsuccessfully trying to solve it since then, so maybe it’s time to ask for some help. I’ve changed the quantities :) 1. Homework Statement The mass of puck 1 is ##0.2\ kg## and that of puck 2 is ##0.25\ kg##. The...

Homework Statement A 0.160 kg ball makes an elastic head-on collision with a second ball initially at rest. The second ball moves off with half the original speed of the first ball. a) what is the mass of the ball b) what fraction of the original kinetic energy gets transferred to the second...

Homework Statement m1= 3kg m2= 6kg v1 = 5m/s v2= 2m/s d = 3m DIAGRAM : http://gyazo.com/17b3126726b109256a35f65b86708bb0 Homework Equations Conservation of momentum: m1+v1 = m1v1'+m2v2' Conservation of elastic: m1v1^2+m2v2^2 = m1v1'^2+m2v2'^2 The Attempt at a Solution Now my attempt...

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...

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 An assembled system consists of cart A of inertia mA, cart B of inertia mB, and a spring of negligible inertia, clamped together so that the fully compressed spring is aligned between the front end of cart B and the back end of cart A. The internal energy of the system...

Now I know that in the general Schwarzschild metric, there is energy and angular momentum conservation, but what I'm wondering is if there is any linear momentum conservation. Let's say a particle collides with a black hole. Does the energy of that particle go solely to the rest mass and...

Hi, I am trying to wrap my head around what happens when a ball of mass m bounces against a hard floor. I assume a system that includes the ball and the floor (and eventually the entire planet) and an elastic collision. Before the ball hits the floor it has a momentum of mv. After the bounce...

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

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...

Homework Statement Suppose that a certain accelerator can give protons a kinetic energy of 200 GeV. The rest mass of a proton is 0.938 Gev/c^2. Calculate the largest possible rest mass M0 of a particle that could be produced by the impact of one of the high-energy protons on a stationary...

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...

Lets say i have a rod (length = L) hinged at one end (A).It is initially at rest.Now if an impulse (J) acts on the other end (B),can i conserve the angular momentum about A(the hinge)? that is can i write: JL=Iw?(I=moment of inertia,w=angular velocity) this is what i saw in the book. My Doubt...

Hey all, Simple question yet it creating a lot of confusion in me and I need some clarification. This is an example given in a book I'm reading and I just don't understand one piece of it. In the S frame a completely inelastic collision between two particles traveling at each other at speed u...

I was recently reading about the Meissner effect, in which certain superconductors are able to "exclude" any external magnetic field lines from their interior, as seen in the right half of this diagram: I understand that some superconductors exhibit a sort of imperfect Meissner effect in...

Homework Statement A billiard ball of mass M is initially at rest on a horizontal frictionless table. Another ball of mass m < M and velocity ##\vec{v}## in the positive x-direction hits the first ball in a pefectly elastic collision. After the collision, the balls move with (unknown)...

Homework Statement A billiard ball of mass M is initially at rest on a horizontal frictionless table. Another ball of mass m < M and velocity ##\vec{v}## the positive x-direction hits the first ball in a perfectly elastic collision. After the collision, the balls move with (unknown) velocities...

Homework Statement A grenade is rolling due west at 0.954m/s along a floor when it explodes into three pieces of equal mass. The first piece moves at 3.6m/s, 20° [N of W]. The second travels at 5.8m/s, 62° [S of W]. Calculate the velocity of the third piece.Homework Equations P=mv...

So I've recently read Newton's third law violates the principles of relativity. I only know how to prove conservation of momentum if Newton's third law holds. I was hoping someone could explain to me this (proving conservation of momentum when Newton's third law is false) without using extremely...

Homework Statement A disk with momentum of inertia I1 rotates with angular velocity Wi about a vertical friction less axle. A second disk, with moment of inertia I2 and initially not rotating , drops onto the first. Because the surfaces are rough, the two eventually reach the same angular...

Homework Statement A 45 rpm record in the shape of a solid disk 25 cm in diameter and mass 0.1 kg rotates about a vertical axle through its center. A 15 g spider rides along the edge of the record. Calculate the final angular speed of the record if the spider drops off without exerting a...

I learned that momentum conservation is vectorial, and now, when i read about perfect elastic collisions, I can't understand why they use a scalar conservation. I tryed to use vectorial coervation to see the diference and it's true: it's needed a scalar conservation. But why?

http://imgur.com/QhYG54l The image seems to be not showing here is the link : http://imgur.com/QhYG54lWhat does Landau mean here by the Lagrangian remaining ''unchanged''. Is it the value of the lagrangian as a function that may not change or is it the form that may not change? Also how does...

If a moving point mass collides with a point mass at rest then you can find the resulting velocities by conservation of momentum and conservation of kinetic energy. Are the accelerations in this case said to be infinite in the sense that the changes to the velocities happen instantaneously?

Homework Statement A machine gun held by a soldier fires bullets at the rate of three per second. Each bullet has a mass of 30 g and a speed of 1200 m/s. Find the average force exerted on the soldier. Homework Equations FΔt = mgf-mgi The Attempt at a Solution I attempted to do this...

Homework Statement A 2200-kg van traveling north along the interstate at 25 m/s is involved in a perfectly inelastic collision with a 1500-kg automobile driven by a careless motorist who emerges at a speed of 15 m/s form an entrance ramp that makes an angle of 20 degrees with the highway. Find...

Homework Statement A 7-g bullet is fired into a 1.5-kg ballistic pendulum. The bullet emerges from the block with a speed of 200 m/s, and the block rises to a maximum height of 12 cm. Find the initial speed of the bullet.Homework Equations conservation of momentumThe Attempt at a Solution First...

Homework Statement The combined weight of a small boat and a hunter is 1200 N. The boat is initially at rest on a lake as the hunter fires 75 bullets, each of mass 0.006 kg. If the muzzle velocity of the rifle is 600 m/s and frictional forces between boat and water are neglected, what speed...

Homework Statement A uranium atom of mass 238 u decays by emitting an alpha particle (the nucleus of a helium atom) of mass 4 u at a speed of 2 x 107 m/s. (Note that "u" is the symbol for atomic mass units and 1 u = 1.67 x 10-27 kg.) What is the recoil speed of the resulting nucleus immediately...

Homework Statement I don't understand how momentum is conserved in Newtons cradle. If I look at the component vectors for the initial ball on the left that I raise, one component points down and one points to the right but then looking at the vector components on the ball that moves on the...

Hi, if a ball spinning on a rod hits another similar ball (m1=m2) what is conserved linear p or angular L momentum? Thanks

Hey all, I'm brushing up on some physics in my spare time, and I was wondering if someone knowledgeable here could help me clarify the reasons behind a couple answers...much thanks in advance! =) Question 1) The greatest linear acceleration of the center of mass of a baseball bat will be...

Homework Statement Box A of mass 1.20 kg is sliding to the right across a frictionless table at a speed of 2.52 m/s. Box A collides with Box B which has a mass of 2.56 kg, and Box A bounces straight back to the left with a speed of 0.665 m/s. A) What is the momentum of Box A before the...

First post here. This question has two parts. (1) Connecting the dots between the Impulse-Momentum Theorem and the Law of Conservation of Momentum and (2) Book recommendations for a more theoretical treatment of classical mechanics? (1) Difficulty reconciling the Impulse-Momentum Theorem...

Is the law of conservation of momentum underpinned by the law of conservation of energy?

Homework Statement A 1500-kg sedan goes through a wide intersection traveling from north to south when it is hit by a 2200-kg SUV traveling from east to west. The two cars become embeshed due to the impact and slide as one thereafter. On-the-scene measurements show that the coefficient of...