Q.8. A boy is holding a book of mass 500 gm by pressing his two hands against the two opposite vertical faces of the book. If coefficient of friction between his hand and the surface of the book is 0.2, and if he exerts equal forces in opposite directions by his two hands as shown in the figure, the minimum force (F) he has to exert, in order to stop the book from slipping down is

(A) 5 N
(B) 100 N
(C) 20 N
(D) 12.5 N