A hypodermic needle is 2.98 cm in length and 0.28 mm in diameter. What pressure difference between the input and output of the needle is required so that the flow rate of water through it will be 1 g/s?

Answer 1

The equation you need to answer that question can be found at:
http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

You will need to look up the viscosity of water. Assume room temperature.