A steel ring of radius r and cross section area A is fitted on to a wooden disc of radius `R(Rgtr)`. If Young's modulus be R, then the force with which the steel ring is expanded is

Explanation

Original length, `l = 2pi r , Extension, Delta l =2 pi R - 2 pi r = 2 pi (R -r)`
` Strain = (Delta l)/(l)= (2pi (R -r))/(2pi r) = (R - r)/(r )`
Young's modulus,` E = (F//A)/((R -r )//r) or F = EA ((R -r)/(r ))`