Calculating Acceleration Rate in a Decreasing Pipe

[elementG]

Homework Statement

A pipe is designed to have its cross sectional area decreasing linearly from 12-inch diameter to 6-inch diameter. What is the acceleration rate at a section 10 inches from the ending section of 12-inch pipe at time = 3 sec? The volume flow rate Q=2t cfs (note: t is in sec). Also given is the length of pipe from the 12-inch diameter to the 6-inch diameter is 30-inches.

Homework Equations

Might use a_x = du/dt

The Attempt at a Solution

Tried solving Q by letting t=3 and substituting into the Q equation to get 6 cfs, but it hasn't led me any where.

 

[wilkr]

I have a similar question in my Fluid Mechanics book.
Diameter of duct changes linearly over a length of 3m, being 0.46m at entry and 0.15m at outlet. If flow is steady and volume rate of flow is 0.3m^3/s, determine rate of acceleration of fluid at a point halfway along duct.
Determine total rate of acceleration at same point if volume rate of flow increases at 0.37m^3/s^2.

How do you calculate this?