(e) (10%) Simplify the equations if steady, inviscid, and 2D flow (x-y coordinately only)

(a) (10%) What is the definition and meaning of D/Dt?

(b)(10%) In this flow, is it compressible? Why or why not?

(c) (10%) Simplify the equations if steady

(d)(10%) Simplify the equations if steady and inviscid.

3. (10%) A steel rod with an initial carbon concentration 0.2% by weight is to be hardened. An equilibrium concentration of carbon in iron at the phase interface of 1.5%. Calculate the time required for the location Imm below the surface to have a carbon mass concentration of 0.8%. The diffusion coefficient of carbon in steel at the process temperature is . Hints: The similarity variable for this problem is , and the erfc(x)= 1 - erf(x)

一、 根據一些社會學研究指出，健康有其社會基礎，亦即健康與階級、性別及族群（或種族）具有密切的相關。試分別舉出一個以上日常生活中的例子，說明這樣的關係。

二、 近十餘年來，台灣社會也跟隨世界潮流，興起了新的社會運動。試舉一例，就其新議題、新組織形式、新行動戲碼及新組成份子，加以分析並評論。

(1) Brexit

(2) BOT

(1) What causes the longest-ever U.S. Government shutdown from December 2018 to January 2019?