IIT JEE , AIEEE Forum - Physics , Mechanics

Asmita

A thin half disc is placed in x-y plane as shown.The centre of mass lies at pt. (a,b). Then find a & b.

joyfrancis

a=-2r/pi
b=0

aman23iit

hi this is a very good Q

do you agree that b=0

as it is a line of symetry

now we have to find a

now consider a small ring of width dx

i hope you know the formule for finding the centre of mass

i.e Xcm=_^X(l)dl/dA here y(l) are the centre of mass of the thin strips

which is given by2x/pi

hence

you have to integrate Xcm=(

xdx.2x/

)/

R²=4/3.R/

plzz rate me as i am new

bye

Asmita

U almost got it right. U only forgot 2 consider the -ve sign of a.

The ans. is a= -4R/3

& b=0.