IIT JEE , AIEEE Forum - Physics , Mechanics

Lois

Please help me with this question

Is the statement true or false? State reason.
The centre of mass of a system of particles is at the origin. It follows that if there is a particle on the positive X-axis, there must atleast one particle on the negative X-axis.

Thanks,
Lois

vinu

Hi lois,

The statement is false.

Since , no of particles is not restricted,

u can have 2 other particles lying in Q₂ such that these 3 particles form an equi triangle .{where COM is the centriod}.

Aatish

at centre of mass, vector sum of mass momenta of all particles is zero, therefore if centre of mass is at origin, m₁r₁+m₂r₂=0. therefore r₁ = -m₂r₂/m1

which implies that if r₁ is negative r₂ is positive and vice-versa.

Aatish

hey vinu, lois is talking about possibility not particular.

Lois

A body has its centre of mass at the origin. The x-coordinates of the particles
(a) may all be positive (b) may all be negative (c) may all be non-negative (d) may all be positive for some cases and negative in other cases

Aatish

(d) is correct

Lois

the answers are (c) and (d) (HCV) please answer experts

krishna.gopal

For the first question, Vinu has given right answer. The question says that "there must be a particle on - x-axis" which is not always necessary.
And Lois you can post only one question in a thread

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