explain linear momentum of system is zero in centre of mass frame of reference?
436809
i'll give an example for this...\na man running in a big planet like the earth. earth as we all know rotates. this is the mass frame of reference since the earth is a larger mass, the movement of the planet is neglected by the movement of a smaller mass like a man running on it.
871846
For an object to be in mechanical equlibrium, the forces acting on it must be zero per standard definition.\n\nHowever, there is a good, short discussion on this topic in Wikipedia, the free, online encyclopedia:\n\nhttp://en.wikipedia.org/wiki/Mechanical_equilibrium\n\nQuoting:\n"A standard definition of mechanical equilibrium is:\n    A system is in mechanical equilibrium when the sum of the forces, and torque, on each particle of the system is zero.\n\nA particle in mechanical equilibrium is neither undergoing linear nor rotational acceleration; however it could be translating or rotating at a constant velocity.\n\nHowever, this definition is of little use in continuum mechanics, for which the idea of a particle is foreign. In addition, this definition gives no information as to one of the most important and interesting aspects of equilibrium states – their stability.\n\nAn alternative definition of equilibrium that is more general and often more useful is\n    A system is in mechanical equilibrium if its position in configuration space is a point at which the gradient of the potential energy is zero. "\n\nHope this helps!
771242
I believe so.  The formula for momentum is mass * velocity.  If your mass is zero or velocity is zero, this will make your kinetic energy zero as well (formula for kinetic energy is 1/2 * Mass * velocity squared).  Momentum and kinetic energy both deal with movement.
165906
yes.  When the net force is zero, this means that it is in equilibrium, and therefore the forces on the object must be the same.  The saying everything up equals everything down, and everything left equals everything right applys here.
486047
If after collision the mass goes to rest i.e. no velocity then momentum is zero.
66594
everyone else is pretty much right, it's just that everything in the universe is relative to an object's frame of reference. nothing is absolute. for example, you're on a bike moving at 10 m/s. you throw a baseball at 15 m/s relative to your frame of reference. to someone standing nearby, from their frame of reference the ball is moving at 25 m/s (the 15m/s you threw it at plus the velocity you're already moving.)  now, to a car moving slowly along the road at 25 m/s, the ball is not moving at all. it is stationary in the frame of reference of the car because they are moving at the same speed as each other. this is why it doesnt feel like you're moving backwards when you're in a car at a constant velocity(only when you speed up or slow down). also, if you drop a book in a moving vehicle, it will go straight down, not down and to the back.  that is because everything in the car is moving at the same speed, they're all in the same frame of reference. if you were to drop a  ball outside of the window of the car(assuming no air resistance) the ball would be moving at the same speed as the car and continue bouncing alongside the car(in reality it slows down substancially due to air resistance.) to you the ball would be stationary, aside from bouncing up and down, but to an outside observer, it would be moving forward.  it's all relative... that's the basic concept but there's also a lot more, more advanced applications involving the distortion of time as you reach near-light speed velocities... pretty interesting stuff.
46266
When it is said that that the net force is zero, it means yes, there is gravitational forces acting at the cenetr of the earth, but being at the center, with equal amounts of earth mass in every direction, the forces pulling on you at the center would all cancel each other out, resulting in the <perception> of having no forces acting on you, when in reality, gravity is always at work.
888567
a) zero momentum, as velocity on top is zero. p=mv\n     p=0.100kg * Om/s\n\nb) Vf = Vi + at\n      0=15+(-10)t\n     t=1.5ec (to reach maximum height)\n\nDivide by 2 for halfway up .i.e 0.75ec\n\nVf = Vi + at\nO=15 + (-10)(0.75)\nVf = 7.5m/s\n\np=mv   (p = momemtum)\n\np = (0.100kg)(7.5m/s)\np = 0.75kg*m/s, upwards (Direction is important)
862651
When the pendulum reaches the 90 degree point in the motion, the force of gravity and the applied force are equal for an infintesimal moment. \n\nThat means there is no "weight" to support. Weight is a function of mass and the force of gravity. Since gravity = 0 relative to the object, then weight = 0
458509
Conserve both momentum and total energy (i.e., potential energy plus kinetic energy).\n\nMy coordinate system will have the pendulum lifted to the left and the block on the right moving left, so that the initial momentum is - M2 Vo2.\n\nIt will also have the block at height 0, so the initial potential is M1 g h where h is the initial height of the pendulum, which looks like L(1 - sin(10 degrees)).\n\nThe initial kinetic energy is of course (1/2) M2 (Vo2)^2.\n\nSo ...\n\ninitial momentum: - M2 Vo2\ninitial energy: M1 g h + (1/2) M2 (Vo2)^2\n\nAfter the collision the potential energy has decreased to zero, and if w is the combined velocity of the two masses then ...\n\nfinal momentum: (M1 + M2)w\nfinal energy: (1/2)(M1 + M2)w^2 + [the energy "loss" from the slight heating and deformation of the two masses sticking].
1117792
Let's make this simple: \n\nInertia and Momentum refer to Newton's 1st Law...Momentum tell us that an object in motion will stay in motion, and inertia tell us that an object at rest will stay at rest...both until acted upon by an unbalanced force.\n\nKinectic energy refers to the energy of moving objects.  (as opposed to potential energy, that refers to objects that are not moving, but that could move.)\n\nExamples:  \n\nInertia:  A pencil sitting on my desk will not move until something moves it.  This is a very comforting thought if you stop and think about it.\n\nMomentum:  If I'm riding my bike, I will continue to move until the force of gravity pushing down on me, and friction moving against the tires, and the wind blowing in my face all conspire to stop me.\n\nKinetic energy:  This is the sum total of all the energy spent keeping my bicycle moving...my legs pedaling, gravity pushing me down the hill, then subtract the forces acting against me.\n\nHey, it ain't rocket science...it's easy!
95497
This a momentum question.\n\nRemember momentum is:\n\nm * V\n\nm = mass\nV = velocity\n\nSo the conservation of momentum is:\n\n(m1 * V1) + (m2 * V2) = (m1 * V3) + (m1 * V4)\n\nMomentum (before collision) = Momentum (after collision)\n\n(Notice mass does not change after the collision, but velocity does.)\n\nSo let's plug in the variables:\n\nm1 = 2.0 kg\nV1 = 3.5 m/s\n\nm2 = 4.5 kg\nV2 = -5.0 m/s \n(negative indicates object is traveling to the left)\n\nV3 = ?\nV4 = -1.8 m/s\n\n(2.0 * 3.5) - (4.5 * 5.0) = (2.0 * V3) - (4.5 * 1.8)\n\n(7) - (22.5) = 2(V3) - (8.1)\n\n-15.5 = 2(V3) - (8.1)\n\n-7.4 = 2(V3)\n\nV3 = -3.7 m/s \n\n(the negative sign just indicates direction with relation to the axis; in this problem, negative indicates the object is traveling to the left)\n\nSo Object A will be traveling to the left at 3.7 m/s after the collision.
819927
All objects react as if there were only a single force acting upon them. Let's say an object on your desk had a force of ten newtons pushing it to the east. Let's call that force positive 10 newtons. According to Newton's second law, it would accelerate (pick up speed) moving in an eastward direction. It had a single force acting upon it and since there was no opposing force we say that it was an unbalanced force. Now say the same object had another force of 10 newtons acting on it in a westward direction. Lets call that force negative 10 newtons. Now we have two forces and since they are equal but have opposite signs the algebraic sum is zero ([+10N] + [-10N] = 0). We now have balanced forces - equal but opposite. Remember I said that all objects react as if there were only one force acting upon them? Even though there are two forces acting in opposite directions on the object on your desk, that object reacts as if there were only one force acting upon it - a force of zero newtons. BTW, that sum force is called the resultant. So according to Newton's first law since a zero force is applied to the object it will remain at rest. In short, unbalanced forces result in movement, balanced forces don't.
943735
a) T = dL / dt = 16\nL = 16 t \n\nI don't think you can do any better than that since they don't ask for the angular momentum at a particular moment in time, and it certainly is not constant.\n\nb) L = Iw\nw = L / I = 16 t / I = 16(33 * 10^-3) / (1.2 * 10^-3) = 440 rad/s
547508
No. \nThe system is static and the sum of the forces equal zero, but there definately are forces flowing through the bar.  Replace the bar with a piece of plastic and then what happens.  The system is no longer in equilbruim, becomes dynamic and the plastic gets torn to shreads.  The same would be true if say you used a piece of wire.  Just because something is not moving does not mean there are no forces flowing through it.
658520
When looking at analogous equations between linear motion and rotational motion, the analogue of mass is the moment of inertia in a rotating system.\n\nFor a single point of mass, the moment of inertia is equal to the mass of the object times the square of the distance to the rotational axis.\n\nFor an arbitrary body, you need to integrate [the product of the density and (the distance to the rotational axis squared) ] over the entire volume of the body.  Since it's hard to write math notation here, I suggest you look at the formula on the source pages (it's the first formula on the scienceworld source).\n\nFor certain common shapes, formulas are given on the pages listed by the other answerers, as well as, for example, here: http://en.wikipedia.org/wiki/List_of_moments_of_inertia
106773
depends on the acceleration of the airplane or object. this found by vector addition. example: if an airplane or a rocket is falling freely (god forbid) all the objects inside will have 0 weight.