Water flowing through a 2.8 cm-diameter pipe can fill a 200 L bathtub in 5.8 min.

Flow rate Q = volume/time = speed * cross section area
Q=200/5.8=speed*.028....i get 1231.52
or
Q=(200/348)=speed*.028...i get 20.52

both are wrong so what do i do?

2 answers

crosssection area of a pipe is not the diameter. It is PI(diameter/2)^2

but besides that, you need to change Liters to a dimension cubed.

I think working in decimeters^3 will be best.

200dm^3=speed*PI(diameter/2)
=speed*PI(.25dm/2)^2

speed=200/(PI*.125^2) in dm/sec

Think that out, why it is right.
ok so i did speed=200/(pi*.25^2) ...i got 3.97 which is wrong
maybe because i have to get the answer in m/s