IIT JEE , AIEEE Forum - Physics , Mechanics

umang

more than one correct -

P is the COM of mass of 4 point masses A,B,C and D , which are coplanar but not collinear .

(a) P may or may not coincide with one of the point masses

(b) P must lie within the quadrilateral

(c) P must lie within or on the edge of atleast one of the triangles formed by taking any three of A,B,C and D

(d) P must lie on a line joining two of the points A,B,C,D

anirudh1990

by the laws of centre of mass: p should lie entirely within the quadrilateral, it may or may not coincide with any of the points.
so the answer is:-(a)&(b)

konichiwa2x

a,b and c are correct.

rajiv_nag

(a),(b)&(c) are correct.
(a) can be correct for concave polygons only.
(b) is explained.
(c) &(b) do not make any difference.

consider A & B on X & Y axes. res.
you get the position vectors. let C be the origin.
verify each option with the position vector of CM.
you will get the result.

umang

Hi all ,

well , the answer i hav says (a) and (c) are correct !!!!!

anirudh1990

Hey Umang the centre of mass always within the boundaries of the system. then how can it be that the com lies outside?

umang

Hey ,

I got how (b) is not the answer , but before I tell u, tell me the basic definition of a quadrilateral

umang

Hey ,

Is their no one who wants to know the answer ?????????

I dont think their is a need to tell u the answer if u r not interested !!!!!

vinu

Hey c'mon UMANG.........
don't get frustated !!!
tell me the ans please.......
I cudn't figure out how to eliminate the options.

P.S:Do give a detailed solu plzzzzzzzzz

umang

Hi vinu ,

Ok , here is the solution -

the correct options are (a) and (c) . But before telling that why (b) is not , pls tell me the basic definition of a quadrilateral . Does it mean figure formed by 4 non-collinear points ???????

Reply soon !

umang

Hey vinu ,

I am waiting for the reply !!!!!!!!!!!!!!!!!!!!!!!!!!!

umang

Hey yaar ,

why r u not replying ??????

Anyways , what i thought was, Join 12341 Is this a quadrilateral ????

1

2 4

3

If yes , then its COM may not lie inside !!!!

Hence , (b) will be wrong

KAB

But umang we can think of many quadrilaterals like13241 in which COM may lie.

umang

Hi KAB ,

Yes , it may lie within , but the option (b) says it must lie , hence it is wrong !!!

AAKRITI

i have come to the following conclusions

(a) is right

(b) is wrong

(d) is wrong

but i am not able to decide about (c) , someone please exlain

Ask & Discuss Questions with Community & Experts