The stiffness of a beam of rectangular cross section is proportional to the breadth and the cube of the depth. If the breadth is 20 cm, express the stiffness as a function of the depth.

Question

anonymous · Answer

what are your choices

anonymous · Answer

there is no choices

jhonyy9 · Answer

i am not sure that i understand it right but my opinion is 

let s = sriffness of a beam
     b = breadth
     cube of the depths = d

so we know that breadth = 20 cm

 and that s is proportional to the b and d 

so than now can you writing this proportionalitie of these terms ?

jhonyy9 · Answer

are you here ?

jhonyy9 · Answer

the cube of the depth mean the depth cubed so d^3 ?

jhonyy9 · Answer

so than we can wriiting 

s/b = s/d^3 

s/20 = s/d^3

s^2 = 20d^3

s = sqrt(20d^3) = 2dsqrt(5d)

s= 2dsqrt(5d)

sorry but i am not sure that i have understood it all right