What is the Correct Equation for Flow Rate?

[foo9008]

Homework Statement

the equation of flow aret given is [(pi)((r_o)^4 ) / 8μ ] [-d/ds (ρ +yz ) ] , but the ans that i got is - [(pi)((r_o)^4 ) / 8μ ] [-d/ds (ρ +yz ) ] , what's wrong with my working ?

Homework Equations

The Attempt at a Solution

 

[BvU]

Try the simpler $$\int_0^{r_0} (r_0^2 -r^2)\, r dr $$to avoid things like the $r_0^3$ (?) in your first step

 

[foo9008]

Try the simpler $$\int_0^{r_0} (r_0^2 -r^2)\, r dr $$to avoid things like the $r_0^3$ (?) in your first step

thanks , i got the ans already