q 30....

balance all horizontal forces( person in equilibrium)

therefore N1=N2 (N1 and N2 are the normal reacns of the walls exerted on the man, N1 by 1st wall, rightwards n N2 by 2nd wall leftwards)

also, by Newton's Third law, N1=force exerted by man on first wall n N2= force exerted on 2nd wall

 

limiting friction acts at the contacts

 

therefore,

f1(vertically upwrds at the surface of contact of main wid 1st wall to balance his weight)=0.8*N1

f2(second wall)=0.8*N2

=0.8*N1

 

mg=f1+f2=2*.8*N1=1.6*N1

N1=400/1.6=250N