floor is smooth and wall is rough

floor is rough and wall is rough

both floor and wall are rough

both floor and wall are smooth

nature of surfaces only

area of contact only

both (a) and (b)

none of the above

1

e2*

e4*

e*72

1/4

1/3

3

4

only (i)

only (ii)

both (i) and (ii)

both (i) and (iii)