momentum is always conserved no matter what happens.the initial and the final momenta of the system are always the same.when a body is at rest,its initial momentum is zero but the final momentum also remains zero.here is an example for you

 

whenever we begin to fire a gun,before firing the gun-bullet system is at rest.when we start firing,the bullets of the gun move in forward direction and the gun recoils back in the opp. direction.this is so as to make the net momentum zero.note that the internal forces of the system are always zero as they cancel each other and are equal and opposite.

 

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the correct definition is this one

 

it is a device which converts chemical energy of an incomplete redox reaction into electrical energy.

hope this helps,plzzz do rate me.

i will definitely rate those who would give the correct answer.

 

1.find the equation of the circle which passes through (1,-2) and (4,-7) and having centre on the line 3x+4y-7=0 ?

answer is 27x*2 + 27y*2 -310x +138y+451=0

 

2.find the equation of the circle of radius 5,whose centre lies on the x-axis and which passes through the point (2,3) ?

answer is x*2 + y*2 -12x +11=0 and x*2 +y*2 +4x -21=0

 

please explain the steps also.

ortocenter is the pt.of intersection or concurrence of the threealtitudes of a triangle drawn from the vertices to the opposite sides of the triangle.

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friction basically means to oppose the motion of a body on a surface.since on a smooth surface there is no oppose to movement hence friction is zero.

e.g. if you roll a ball over a smooth frictionless surrface in vaccum it will keep on rolling forever.

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this is due to the fact that the unit of charge has been defined by the international units of system (or S.I. units).c.g.s. units and s.i. units are totally

two different things.